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No Fizz
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| First it's nice to know that the amount of carbonation in KT has virtually no effect on the efficacy of the ferment. I say virtually because the impact is minor and arguments can be made both pro and con as to the effects of carbonation. And I might add that the presence of fizz in no way indicates whether the fermentation proceeded properly. If you're getting good SCOBY thickness but no fizz, this is actually a good thing since you have enough yeast to keep the bacteria happy and not enough to overwhelm them.
That said, what is reasonable to expect from a "normal" KT ferment? After 3 or 4 cycles of fermentation it is customary for KT to reward you with some bubbles. It can happen on the first cycle but this is entirely dependent on how the culture you received was generated, the handling prior to you receiving it as well as how you handle it.
A "balanced" ferment - and you'll hear me use that term a lot, will produce a fair amount of bubbles which will be evident when you pour it into a container and it produces some foam, similar to what washes up in the ocean on a windy day. In extreme cases it will come out like beer but that is unusual and may indicate an overabundance of yeast. Normally the bubbles will be barely noticeable by the palate when sipped directly from fresh ferment but it will have a quality that is much different from flat KT and much more desirable to the palate.
Often new users will experience flat KT initially because the yeast population hasn't enough variety or it hasn't hit that critical number to produce good fizz. They will eventually show up after successive brews, some are airborne others may be reluctant to reproduce due to being in a state of dormancy. There are a few things you can do in the mean time to help inspire them.
Different types of yeast produce more CO2. Too much sugar can decrease the amount of CO2. Weak tea will reduce the amount of carbonation. The type of tea can impact carbonation and temperature will affect carbonation.
Yeast normally shifts from CO2 production to alcohol production under two conditions. The first is lack of surface and dissolved oxygen the second is an overabundance of glucose. Therefore wire whipping or other forms of aeration prior to setting up a ferment or using a little less sugar can help increase carbonation in the early phases of fermentation.
Once the yeast fully populate, adding a little more sugar will get them going. You can do this half way through the fermentation cycle or just prior to bottling. Be conservative if you do it during bottling because you need only a tiny bit to create a grenade! I recommend a quarter of a teaspoon per quart. Some people add a couple of raisins or slices of ginger to a ten ounce bottle both of which work well.
If your brews are still sweet when you take them off let them go a little longer until they're real tart. You may find after a few extra days you will see a few tiny bubbles begin to show and rise to the surface. Use a flashlight and look very carefully. If you spot even one or two you're ready to bottle.
For world-class carbonation you need to bottle at room temp for 48 to 72 hours prior to refrigeration. See the section on Two Stage Bottling for best results. Keep in mind if you store KT in a container that is not air tight it will eventually go flat just like any beer or soda would.
When you make your next batch use starter from the bottom of the last fermented batch. It will have more yeast. Use at least 20% starter until the fizz begins to show up better, and then you can back down to 10%. Also allow your starter to sit open at room temperature for 3 or more days (cover it with a sheer cloth, panty hose or paper towel.) This insures activity is high and allows airborne yeast a chance to take residence.
If you've been using all black tea, try some different varieties. Green, in general, is superior for carbonation but you may want to mix it with black for a better taste. I recommend a 3 to 2 ratio of green to black for best results.
Get the temperature up to about 82 degrees if you can until the yeast get a strong hold and fizz begins to show up. Then drop it back down to 72-75 degrees thereafter to make sure the balance of the ferment doesn't tip to too much to the yeast. This can be a much bigger problem and take time to remedy. Some experts consider 73.5 degrees the optimum for culture balance and my own experience seems to prove that out. I like the improvement in flavor the lower temperatures bring but you will often sacrifice carbonation at lower temperatures.
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Too Much Fizz
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| Too much carbonation is usually accompanied by premature souring, malformed SCOBYs and low concentrations of gluconic acid. Most beginners usually want to know how to increase carbonation rather than reduce it. But with successive brews often the yeast will become over stimulated, especially in the warmer months.
Normally as a result of how KT is prepared, the yeast tends to go into fermentation early and begin producing alcohol along with relatively small amounts of CO2. But in the warmer months the likelihood of yeast being in respiration increases.
In respiration the yeast produce 3 times as much CO2 as in fermentation and no alcohol. They also burn oxygen and glucose at a higher rate. As a result the bacteria don't get the alcohol they use for fuel and to make matters worse they must compete harder for the available oxygen and glucose.
Now without alcohol, bacteria must rely solely on glucose and air to reproduce. But with the yeast in respiration this makes oxygen scarcer. As a result of this, the acetobacter reliance on surface air to produce cellulose and gluconic acid increases. Since CO2 is being generated at a higher rate it tends to pool on the surface and crowd out the oxygen. So the SCOBY may begin to form but, with it harder to locate surface oxygen, growth slows to a crawl.
So what can you do to decrease CO2:
- Increase the available glucose
- Decrease the strength of the tea
- Reduce the temperature
- Reduce the yeast population
The first two of these are a little less obvious and they also tend to oppose each other. This is because reducing tea reduces the nutrients yeast need to manufacture the enzymes, which cleave the sugar into glucose and fructose. So this can actually reduce the available glucose. However reducing the tea still tends to work because the yeast become less likely to respire and instead use the energy for producing alcohol which is what we want.
If you reduce the tea's strength it's even better to add some glucose directly in place of a portion of the sugar. This will insure the yeast enter into what the brewing industry refers to as the "Crabtree effect" where fermentation replaces respiration prematurely. Karo or corn syrup are good sources of glucose, the latter being preferred.
Keep the temperature around or below 22 degrees C (73F) . You can still get good ferments at 18 degrees C (65F) but it can take a week or more longer to produce than at 22 degrees C (73F).
To dramatically reduce the yeast populations see the section below titled "Increasing the Ratio of Acetobacter to Yeast Populations".
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CLOUDY
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The typical thing that causes KT to be cloudy is rapid yeast reproduction. Typically an abundance of CO2 accompanies this effect. The yeast aren't dead or fat enough to sink to the bottom and so they stay in suspension. If you want to clarify the liquid the best thing to do is use the two stage bottling technique I've listed below with one modification. Add just a touch of plain gelatin powder to the first stage of bottling. By the time you enter 2nd stage bottling the liquid will be perfectly clear.
However, even if you don't add gelatin, usually bottled KT will clarify with age so after a few weeks the yeast will just form sediment on the bottom of the bottles. 2 stage bottling with gelatin gives you a chance to remove most of the sediment prior to long term storage.
But beware! By reducing the cloudiness you also weaken the taste.
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SLIMY
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My brother's KT often comes out slimy/syrupy where as mine is always clear and light. I've come to the conclusion it may be due to the chemicals in his city water. (I use straight well water.)
Be sure you boil the water for 10 minutes or more. This will give many chemicals like chlorine a chance to evaporate. Then when you transfer the water leave any heavy silt in the bottom of the pan you boiled in. Of course a good water filter couldn't hurt either.
If you still get slime then it could be the yeast and you may need to choke them out a little. Use extra sour starter; stuff that's fermented about 3 weeks or more and wash your culture in distilled vinegar before using it again.
This assumes you're using the standard 160 grams of sugar per 2 Litres of water. If you're using more than that then don't. In any case, it can't hurt you and most of the slime will precipitate out after it sits in the fridge for a week.
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TOO SLOW
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Here are some of the things that can put the culture into slow motion (in order of likelihood) :
- Low temperatures.
- Too much sugar (or glucose).
- Culture and/or starter refrigerated before setting up the ferment.
- Too little starter.
- Insufficient access to air.
- Overworked dieing culture.
- Cooked culture from introduction too early into warm tea.
- A contaminant.
- Tea type might have an additive that inhibits culture.
If you detect the SCOBY is still growing then it is unlikely the last 5 items apply.In most cases the bacteria are more susceptible to these last items than the yeast. But if you see continued growth, then it's a good indication everything is OK. |
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THIN SCOBY
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| Cool Temperatures, low yeast count, dormant bacteria, over stimulated yeast, impurities, types of tea and seasonal fluctuations can all cause thin SCOBYs. So first let's review the basics then we'll look at a technique that can revive a weakened culture.
Keep in mind seasonal changes will change the response of the culture. I have found early fall and early spring the best time for hearty delicious ferments. Of course this depends on where you live but after a few years of brewing you come to anticipate the effects. The best way to insure you get healthy SCOBY growth is to keep the mother and starter active. Keep the cultures stored at room temperature in ample starter and covered in the usual manner with a breathable material.
Don't wash your fermenting vessel with antibacterial soap. Guess why? That thing that floats on top is made by bacteria and it only takes a bare trace of residual soap to kill the entire culture. If you're a clean freak make sure you rinse well.
If a thin SCOBY is accompanied by a sweet ferment, chances are you haven't brewed long enough. Let it go a couple more days and until the taste is tart. Also with this situation if your temperature is less than 21C degrees (70F) try to get it up a few more degrees to about 23C (74F). As a rule, avoid artificial stimulation because it tends to spoil the taste. Patience is the preferred approach to any kind of heating device.
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HOLEY SCOBY
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If your SCOBY gets holes but still comes out thick, that's great. It means you have ample yeast and bacteria growth along with lots of CO2. Nothing could be finer. If the SCOBY looks weak then you need to swing the "balance" to the bacteria side. See the section below on "Increasing the Ratio of Acetobacter to Yeast Populations".
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LUMPY SCOBY
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This is one of those rare things that happen once in a blue moon. The SCOBY develops an almost uniform lumpy surface that looks like someone laid a wet handkerchief over a bunch of marbles. I've never seen it happen in successive brews and I'm not sure what causes it.
I read something once by one of the renowned KT researchers that this maybe an effect caused by certain tannins that cause the cells to clump. Don't know. . . but I do know it's nothing to worry about and chances are you may never see the effect a second time. If you do, try a different brand of tea.
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NO SCOBY
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Not much you can do in this situation. There has to be at least some surface formation to recover. If you see at least the beginning of a clear film on the surface then refer to the section below titled "Increasing the Ratio of Acetobacter to Yeast Populations". If there isn't then you need to get a new culture and starter from someone.
To avoid facing this sort of thing in future follow these precautions:
1) Don't use antibacterial soap to clean the fermenting vessel.
2) Don't add a culture to hot or even warm tea. The tea should be below body temperature.
3) Don't add any herbs, spices or anything else foreign unless it's known to be safe for Kombucha.
4) Keep the fermenting vessel away from any disturbing fumes such as paint or solvents.
5) Use only pure Kombucha for starter.
6) Make sure you add sugar, not Stevia or any other artificial sweetener.
You can gradually kill a Kombucha culture over successive ferments with ginger, cinnamon and other herbs or household spices. These sorts of things should only be added when you're ready to bottle. Never allow them in your starter.
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DARK SCOBY
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The longer you ferment with the same SCOBY the darker it will get. This is because both the tea and the yeast make it a little darker each cycle. It's fine to keep using the same culture as long as it seems to be making good brews but if the culture begins to shed dark dried looking layers it's probably time to retire it.
Personally, I prefer to use the healthiest looking culture with each brew. Regardless of how many cycles they've been through I pick the whitest, densest culture I have on hand. This ensures my bacteria are always getting the strongest start possible. Maintaining the culture's balance over successive brews dictates we give the bacteria as much advantage as possible. |
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SCOBY SINKS
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This is normal. Some SCOBYs are denser than others depending on how much CO2 is trapped between the layers. Often a sinker will make some of the best brews.
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SCOBY CLIMBS OUT OF POT
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OK the SCOBY isn't really trying to escape but sometimes it can seem that way. This is a sign that there is plenty of yeast activity. Often the SCOBY creates an air-tight seal on the mouth of the container. When this happens and the yeast produce more CO2 than can stay dissolved in the ferment, then the gas starts to push the SCOBY up and eventually lifts it out of the container.
If the culture suspends itself over the liquid due to trapped gas, it's a good idea to push it down gently and remove the gas pocket so that the newly formed SCOBY is in contact with the liquid. Otherwise the bacteria stop doing their job, which means less acids and more alcohol. |
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TOO SOUR OR TASTES LIKE VINEGAR
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The longer a brew ferments the closer it will get to vinegar. Occasionally though it will ambush you by souring faster than expected. If the SCOBY is fat and healthy you probably waited a little too long. Higher temperatures tend to accelerate fermentation and can catch you off guard. Three degrees over the period of a week can shorten the ferment cycle a full day. Many people who live in warmer climates routinely brew in 5-7 day cycles instead of the 10 days typical for a 22 to 24 Degrees C ( 72-75 F) degree range.
However, if a brew sours prematurely, before the SCOBY has a chance to get to about 1 cm (3/8") in thickness, then you have a culture that is becoming unbalanced and the yeast need to be put in check. This is actually pretty common, especially in warmer temperatures. My guess is since the yeast can reproduce with or without surface air they have a slight advantage over the bacteria that rely on air for reproduction.
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TOO SWEET
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As long as you're seeing SCOBY growth allow the fermentation to proceed. This could be due to low temperatures or a semi-dormant yeast population. I've had brews that took up to 3 weeks before they started to get tart. This can work to your advantage because slower brews have a greater likelihood of forming many of the beneficial acids that make KT so healthy for us. Not only that but you'll find the slower a ferment proceeds the rounder and more delicious it turns out.
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NAIL POLISH REMOVER
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Occasionally a brew will smell nasty like some kind of solvent or nail polish remover. This is more likely than not due to the formation of aldehyde by foreign bacteria. You might notice clouding of the liquid when this occurs. It's best to dump the liquid when this occurs and wash the culture well. Unfortunately, since this type of bacteria does well in acidic conditions, there is no guarantee you can get rid of them with successive brews. Try soaking the culture in pure distilled vinegar over night before you use it to make another batch. If the next batch turns out the same, you may want to think about replacing the culture.
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ROTTEN CITRUS SMELL
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Sometimes you may encounter a skunky smell a bit like rotten orange. This often coincides with brewing at higher temperatures. Besides temperature, you might notice this effect is greater the longer it takes for the vessel to seal itself. Until the surface seals off completely (with a new SCOBY) the door is left open for a greater degree of respiration.
During a brew cycle there are two types of activities going on; one is fermentation (anaerobic) and the other respiration (aerobic). When the yeast are very active there is a higher level of respiration going on. Respiration is a complex process that produces a lot of intermediate compounds, one of these being citric acid.Though not desirable tasting this is nothing to be alarmed about. Once the respiration abates, these compounds tend to reconfigure and dissipate. Storing without air, where respiration is impossible, often eliminates this taste after a few weeks. |
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MOLD
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A lot of new comers mistake a forming discolored SCOBY for mould. It's pretty rare to get mould if you're using good starter. So first of all make sure it's mould. As soon as you see a sign, look very closely to see if the surface is fuzzy. If not then let the ferment continue and keep checking for signs of fuzz. If you don't see fuzz, then it's not mould.
Mould is probably the most dangerous threat to KT. This because all mould is not the same and depending on the variety that establishes itself, it can leave the KT poisonous not to mention unpalatable. I am less fearful than most but will still tell you it's a whole lot faster and safer to get a new culture from someone than it is to recover from a mouldy culture.
However for the fool hardy, let me tell you how I recovered from mold. Since mold always grows on the surface of a Kombucha culture and the SCOBY is usually pretty buoyant it makes it easier to isolate and remove.
First throw out the ferment that had the mould. It's useless and too dangerous to consume. If you have another culture throw out the one with mould and start over. Otherwise take the moldy culture and carefully remove all parts suspected of mould without touching the mould. You want to be careful not to accidentally contaminate yourself or your working area.
It's all right if you radically carve up the culture because all you need is a small piece to regenerate a new culture. In fact you might want to carve the culture up into a couple of pieces to run parallel regeneration batches. Take the uncontaminated pieces and submerse them in pure distilled vinegar for a couple of days.
Now you are ready to make a new batch. Make your next batch as usual but use 10% distilled, or pre-boiled vinegar instead of starter. If the next batch forms mould (which it won't, trust me) follow the above procedure again. If no mould develops you can make the following batch as normal using starter instead of vinegar. Don't bother drinking any of the recovery batches. They won't taste good and they may still have trace contamination. But before you make the next batch meant for consumption a few sage words about avoiding mould in the future:
Sanitary conditions are not the answer! At least not practically speaking. More often than not, mould spores are airborne all around us. The question becomes what can one do to increase resistance to mould when fermenting KT.
The only way to protect yourself is by raising the acidity level of the ferment when it is first prepared. This is the number one reason why we add starter. Mould deplores acidity.
Well, many people add starter and still get mould - Why? Some people ferment a much shorter time than others because they prefer the ferment on the sweeter side. As a result the acidity level is lower. This means they increase the likelihood that mould will form before the fermentation acidifies to a level which rejects mould.
Always use 10-15% starter or about half as much vinegar. If you're already using starter there are 3 possible ways to further avoid mold:
1) Add a few tablespoons of distilled, pre-boiled, vinegar gently to the top of the brewing vessel once it's ready to ferment.
2) Use more starter.
3) Use more acidic starter.
This last one I prefer. I do this by using the ferment I store my cultures in for starter. It's usually very close to vinegar. I can use less since it's much stronger. I just replace what I use with fresh ferment so I maintain a constant level and turnover.
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DEALING WITH CHLORINE
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I use well water and after I chlorinated my well it took almost 6 months before my KT started tasting good again. So anything you can do to reduce the effects of chlorine is well worth it. Some water purification systems will help remove chlorine but one thing that always helps is boiling the liquid uncovered for 10 to 15 minutes. Be sure to put on extra water since you will probably loose 10 to 20% during boiling.
Remember KT is half bacteria and most things we do to protect ourselves from bacteria, such as water treatment, sun bathing and antibacterial cleaners are poison to KT. So you want a bacteria friendly environment. This is not as bad as it sounds because Kombucha is extremely good at segregation and when prepared properly will take care of insuring only acid loving friendly bacteria take residence during fermentation.
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DEALING WITH CONTAMINATED WELL WATER
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If your well is contaminated you need a good filtration system which is designed to remove those specific contaminants.
Please permit me that hypocritical moment. Personally, I have decided to live with my well that is both contaminated with bacteria as well as chemicals from the abuse of farmers with their pesticides and nitrogen based chemicals. My rationale - good or bad is, that whatever they put in the ground I've already consumed from the vegetables they grow since I've been eating them my whole life.
As far as bacteria, the best tasting KT I ever made was from this contaminated water before I had the water tested and treated. Now I just boil the water for 10 minutes and the KT tastes pretty good, but maybe not quite as good as before. What can I say, our variety of bacteria tasted pretty good. Actually this is testimony to the power of Kombucha to reject most foreign bacteria. If it can live in KT chances are it won't hurt you and you may already have some of these organisms living inside you.
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BREWING IN HIGH TEMPERATURE
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It's nearly impossible to make good KT at high temperatures. Bacteria start to die above 35 Degrees C (95 F) whereas the yeast will survive to about 49 Degrees C (120 F). So the hotter it is the more likely you're making tea wine. Not only that, but once the static ambient temperature goes above 28 Degrees C ( 82 F) degrees the yeast are usually so active that they out pace the bacteria and cause the ferment to sour well before the most beneficial compounds are created by the bacteria.
However, there are three things you can do to help keep the balance of the culture in higher temperatures. Always use the densest, whitest SCOBY you can find because it will contain less yeast. If you have a choice, use the youngest available.
Next use the oldest, sourest starter available or use pure distilled vinegar. Most of the yeast will have died off in old starter and none will exist in pure vinegar. This will cause the yeast to get off to an extremely slow start and allow the bacteria more opportunity to do their job. It may take your ferment twice as long but the results are much better for you and tastier as well. Of course if you're in a hotter climate that may offset much of the delay and result in your brew times being what the rest of us experience, about 8-10 days. From everything the experts tell us, no matter what the temperature, the majority of the acids, which are really good for us don't accumulate for at least a week. So do everything you can to slow the pace down by dropping the temperature or reducing the yeast populations.
Finally, use a vessel with greater surface area. This will allow large bacteria populations to develop faster and further help maintain the culture's balance.
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BREWING IN LOW TEMPERATURES
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You need at least 18 Degrees C (64F) for a viable balanced culture. Below that the bacteria tend to go to sleep and the yeast will be pretty sluggish and produce nothing but alcohol. However, to a degree the bacteria can adjust and if you see the SCOBY growing that's a good sign that the bacteria have enough energy to build their cellulose homes. The only thing you need is plenty of patience because at colder temperatures it could take 4 or 5 weeks to ferment properly.
Avoid artificial heating because for a good ferment you should have evenly distributed heat. However, if you must heat, do it gently and direct it at the surface where the bacteria collect. But avoid direct lighting especially sunlight.
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TIPS ON HEATING DURING FERMENTATION
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After years of experimenting I take every opportunity I can to slow down Kombucha fermentation. This is because left to itself the yeast tend to dominate the process over time, producing largely acetic acid (vinegar). The faster you brew, the lower the gluconic acid levels as well as several other heavier acids which form later in the fermentation process. Since heating accelerates the process I avoid it as a rule.
That said sometimes there is a need to warm the culture for a while. People who live with their thermostats set below 65 (brrrr..) will find fermentation takes forever. And occasionally a culture that has been refrigerated for more than a few days, or has a very low yeast count, may need a little help to get the populations balanced and fully active again.
In all cases heating should be gentle and kept below 86 degrees. Keep in mind a temperature between 73 and 74 degrees has been proven the most effective for overall consistent KT quality. To stimulate the culture you want to gage how much higher the temperature should be by how much activity your culture is experiencing.
As a routine, heating above 80 degrees is bad for maintaining proper culture balance because it over stimulates the yeast which then compete too heavily with the bacteria for glucose. Heating above 90 degrees will begin to kill the bacteria if done over an extended period. Over 100 degrees and you pretty much guarantee only the yeast will survive if anything.
Also, whether it is to compensate for a cold room or to stimulate a sluggish culture, heating for the first 24 to 48 hours has advantages over heating throughout the entire fermentation cycle. This is because it helps the yeast produce glucose early on before they enter into full scale respiration and reproduction. This allows the bacteria nourishment with minimal competition from the yeast.
If heating will be a habit due to storing the ferment at low temperatures then keep in mind the bacteria tend to collect at the surface where as the yeast will be dispersed throughout the solution. This means if you have an overall weak culture you might want to heat along the sides of the vessel. If over time you find the yeast are more active than the bacteria (indicated by souring without significant SCOBY growth), switch heating to be directed at the surface where the bacteria collect.
You can heat from the bottom also by using a pet warmer mat type of device. This is the least preferred method and should be reserved for very weak yeast populations (indicated by a ferment which sours slowly and produces very meager SCOBY growth.)
Those of you who have normal temperatures to brew in but seek to stimulate the culture because it seems weak or slow should view heating as a short term measure. In fact, if heating gets the desired results for a batch it should be discontinued on future ferments. This is because once the culture gains the necessary strength to ferment and feed the bacteria then your populations have reached critical mass and future efforts will most likely involve reigning in activity to maintain the culture's balance.
Without robbing you of creative ideas on ways to heat your culture, here are the most popular methods I've heard people use:
- Suspend a 25 watt bulb about 1 ft above the surface.
- Wrap the vessel in an Electric blanket set on low.
- Use a pet warmer mat.
The first can be done inside of a cabinet with an accompanying thermometer so you can properly monitor the vessel's environment. The others are not as easy to monitor and control. For this reason I would limit their use to the first few days of fermentation. |
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SEASONAL EFFECTS
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| Seasonal effects can be dramatic. I have found that although summer in general produces the fastest ferments, the best tasting ferments happen in the early fall and early spring. Just ride it out and do your best to maintain the balance of the culture. By taking steps to maintain balance you can neutralize most of the impact that different seasons bring. |
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GREEN VERSUS BLACK TEAS
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In general green teas tend to out perform black tea. They make a fatter SCOBY, a better mix of beneficial acids and they help produce larger amounts of carbonation. However, green teas tend to sour faster and produce an astringent quality that many people don't like. For this reason I use a 3 to 2 mix of green to black. I find the taste a perfect marriage and the results consistently good.
Tea drinkers have told me that it's best to use steep times half as long for green, as you would black. If the temperature is near boiling, 5 minutes for green and 10 for black is adequate. Some prefer much longer. I'm not sure there is a significant advantage by going longer unless you want to use less tea to reduce the caffeine content. I find the taste better with shorter steep times but if you tend to bottle the ferment and store for more than a week you'd be hard pressed to tell the difference by then.
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BREWING VESSELS AND SURFACE AREA
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| Surface area doesn't have that great an impact until you get to the outer extremes. Too little surface area and you might as well be making beer. Too much surface and you loose large amounts of liquid to evaporation and SCOBY growth. However, in general, the more surface area, the faster fermenting can proceed without sacrificing the quality of the beverage.
Keep in mind larger surface areas will sour faster. In general, a one to one ratio of diameter to liquid depth will produce adequate results and tends to be a nice compromise as far as controlling the consistency of the beverage.
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DECREASING THE RATIO OF YEAST TO ACETOBACTER POPULATIONS
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| The bacteria rely on the yeast for alcohol and glucose. Beyond this they need oxygen and trace amounts of nutrients that they can get from the air and tea. So it stands to reason by supplying alcohol and glucose we can reduce their reliance on the yeast while we take measures to impede the yeast. Also, although the yeast can withstand much wider extremes in temperature we can still pick the optimum band for the bacteria where the yeast tends to be more sluggish. This range tends to be in the 18 to 24 Degrees C (65 to 75F) range.
But first it's always nice to start with a strong dense SCOBY. You can raise one through a simple procedure that gradually starves the yeast and bacteria insuring only the strong survive. I like to think I'm grooming a master race of bacteria.
The procedure is simple. Start with a portion of newly fermented tea and place it in your standard size fermenting container or maybe a little smaller so that you have at least four inches of liquid depth. Allow fermentation to continue for 3 more weeks.
At the end of three weeks discard the newly produced SCOBY and filter the contents with a paper towel or coffee filter. If you can find a way to syphon just the top clear portion of the liquid this is preferred but it's not critical because at this point the yeast have mostly died off or gone dormant.
Rinse and wipe clean the container. Then replace the filtered liquid back into the container and continue to ferment for another couple of weeks or until the culture gets to approximately a 12 cm (1/2") in thickness.
Now you're ready to begin fermenting with the new master race. However, to insure the balance remains stable or slightly towards the bacteria side follow these procedures during your normal brew preparations:
Use more acidic starter. I do this by using the ferment I store my cultures in for starter. It's usually very close to vinegar. I can use less since it's much stronger. I just replace what I use with fresh ferment so I maintain a constant level and turnover. If you just created the master race as instructed above, the left over solution is ideal to use for starter. Use less though because it will be extremely acidic.
Keep the temperature below 24 Degrees C (75F). Optimum temperature is 23 Degrees C (73.5F) for an already balanced culture.
Use starter that is taken off the top of any standing ferment to insure you pull from where the bacteria to yeast ratio is the highest.
Squeeze the juice of any new cultures you won't be saving into the new ferment or where you store your starter.
Use weak rather than strong tea strength. Strong tea provides more sterols that the yeast needs to reproduce. If they don't get these compounds from the tea they must manufacture them their selves and this will slow them down insuring the bacteria remain more dominant. Assuming a 10 minute steep for black and 5 minutes for green you should be using no more than 3 regular sized tea bags per quart of tea. If you steep longer use less.
Use Green tea or a 3 to 2 ratio of green to black tea.
If available, add glucose. You can use clear Karo as an imperfect but acceptable source or corn syrup, which I much prefer. If you add glucose keep the ratio about 1 to 7 of glucose to sugar. Keep in mind you only need a little to jump start the bacteria because once the yeast work on the sugar for a day or two there will be an abundance of glucose manufactured typically right up to the 9th day of fermentation.
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INCREASING THE RATIO OF YEAST TO ACETOBACTER POPULATIONS
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Use more black tea.
Pull starter from the bottom of the previous brewed ferment and use plenty of it.
Be conservative on sugar. It's best to start out with a little less sugar and then add more after the ferment has proceeded a few days. This is because once the yeasts break down the sugar into glucose, if too much is in solution the yeast can become sluggish and reproduce more slowly. Home brewers commonly know this as the "Crabtree Effect".
Keep the temperature in the 24 to 30 Degrees C (75 to 85F) range.
For those who like to experiment, use the "Continuous Fermentation" technique. This is where you keep a larger container constantly fermenting by replacing the portion you drink with fresh sweetened tea. You'll need a special container with a spout at the bottom so you don't overly disturb the surface when drawing off some to drink. Always draw off prior to replacing tea to insure you get the best quality beverage.
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INCREASING CARBONATION
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Although some types of yeast tend to produce more alcohol than others, (and subsequently less CO2), carbonation is more so a product of the activity of the culture. CO2 production continues throughout the fermentation as yeasts go through growth and reproduction.
Typically more CO2 is produced by individual yeast prior to reproduction and when the greatest amount of oxygen is available. But an active culture will have yeast at various stages. Also the presence of oxygen becomes less of a factor when there is a dearth of available glucose.
That said the best ways to increase carbonation are as follows:
1) Use the two stage bottling technique outlined below. In a nut shell, the object is to fill bottles to the top with no air gap, seal securely and let them sit at room temp for 48 - 72 hours at which point it's time to refrigerate. This helps increase carbonation without sacrificing the balance of the culture. The rest of the techniques also play toward increasing the yeast population so use these techniques only when Two Stage Bottling fails to produce the desired results.
2) When you make your next batch use starter from the bottom of the last fermented batch. It will have more yeast. Use at least 20% starter until the fizz begins to show up better, and then you can back down to 10%. Also allow your starter to sit open at room temperature for 3 or more days. This insures activity is high and allows airborne yeast a chance to take residence.
3) Use a little more tea. Some compounds, (sterols?) which the tea provides, help the yeast work faster otherwise the yeast must take a time out to manufacture them their selves.
4) Get the temperature up to about 28 Degrees C (82F) if you can until the yeast get a strong hold and fizz begins to show up. Then drop it back down to 22 to 24 Degrees C (72-75 F) thereafter to make sure the balance of the ferment doesn't tip to too much to the yeast. This can be a much bigger problem and take time to remedy. Optionally bottling with a little added sugar, ginger, raisins or other dried fruit does wonders both for taste variations and pumping up the carbonation.
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TWO STAGE BOTTLING TECHNIQUE
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I currently use a two stage bottling technique to finish off my KT fermentation. This method is fairly easy and allows for tweaking the end product along the way to adjust for variation in the fermentation results.
In stage one, plastic bottles are used to store the ferment to allow carbonation to build up, typically over a couple of days following harvest of the ferment.
In stage two, I use glass bottles with plastic lids, which is how I store KT until I'm ready to drink it.
Any size bottles can be used. I prefer 600 ml plastic and 300 ml glass soda bottles. This way I have an exact 2 to 1 ratio when I transfer from plastic to glass. The 300 ml are ideal portions for storage and the 600 ml plastic are easy to handle and they insure there is exactly the right amount for transfer - nothing wasted and no room for air.
Here is the procedure:
1. Coarse filter the ferment. I say coarse because you really don't want to remove everything, just the "ooglies". Some yeast residue has to pass through in order to make carbonation. I prefer a paper towel but pantyhose or linen is just as good.
It's best if the ferment is filtered in one pass for consistent results. Since I brew a gallon, I've always filtered half at a time into a 2 Litre jug which is then used to decanter into individual 600 ml bottles. And guess what I found? After the bottles age, those from the first half usually have little carbonation and the second half are like beer. This is due to more yeast collecting in the filter and being forced through, the closer you get to the bottom of the ferment.
Note: I still filter half at a time but now I do so on purpose. See my tips at the end of this procedure.
2. After the KT has been filtered fill the plastic bottles to the rim leaving as little space as possible for air. When capping, gently squeeze the bottle to remove excess air leaving the bottle just slightly soft when capped.
3. Store the bottles at room temperature and check each day by squeezing the bottle to note the pressure. A good brew should make the bottles hard, (like a basket ball), in one to two days. I have had batches take almost a week when there wasn't enough active yeast.
4. Once the bottles have built up pressure you should refrigerate them for a couple of days to let the yeast go dormant and allow the gas to reduce pressure. This makes it easier to transfer to the glass bottles.
5. After the bottles have chilled a few days, transfer the contents to glass bottles. When pouring, gently pour off the liquid trying to keep the silty yeast residue in the bottom of the plastic bottle for later discard, (it's job is done.)
Take careful note of the rim of the plastic bottle as you pour. Good carbonation should show bubbles forming around the rim as you pour. This is your clue since you don't want to pour so fast that you see it foam when transferring.
Try not to leave space for air. If you have to discard too much residue to fill a bottle, top it off with anything handy - KT, wine, beer, apple juice. It doesn't really matter unless you have to fill more than the last couple of millimeters in the neck. However, the less air is trapped, the more stable the brew over time.
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TIPS
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| I don't like plastic for long-term storage - the taste isn't the same after a few weeks. When I open a plastic bottle for transfer and find it has no bubbles I make ginger ale KT by adding a couple of ginger root slices to the glass bottle during transfer. The ginger will produce significantly more carbonation over time and help compensate for a flat brew. It also tastes great. I rarely add ginger to a highly carbonated batch - some times it comes out too bubbly to enjoy. Or worse, it erupts when opening so you loose half! Making ginger ale KT is actually my favorite. This is why I still filter half at a time. Almost invariably I end up with half ginger-ale, half straight KT when I'm done. However, don't use the ginger ale version for starter, it will kill the acetobacter.
Also when you open the first plastic bottle for transfer, this is a good time to taste test. If you find it too tart you can add a little fructose to sweeten. But be careful and quick about it because if the carbonation is high it will begin foaming as soon as you add the fructose. This is also a good time to add other flavorings besides ginger, such as banana, apple, vanilla, etc. Dried fruit is preferred over fresh since there is less chance of introducing a contaminant that will create off flavors.
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REDUCING CAFFEINE
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Here are things that help reduce caffeine using regular tea.
1. Green tea has almost half the caffeine content as black plus it only requires half the steep time, which means there's less time for caffeine to leach.
2. You can half the content again by cold steeping the tea. After you boil the water, let it cool and then put the tea bags in. Colleen, (Colleen Allen; The late beloved KT researcher and E-author), used to suggest leaving it in the fridge over night but chances are as long as it remains covered it should not spoil over the course of a day. At room temp 8-12 hours should do the trick. (Make sure you leave the sugar out during steeping.) To be extra safe you could even add some sour starter at this point to further protect against mold.
3. Instead of cold steeping another neat idea is to pre-steep the tea bags in boiled hot water for 30 seconds and then re-steep in fresh hot water. Most of the caffeine will be washed out in the pre-steep so you're left with decaf in the second steep.
4. Some of the tea experts on this list or a little research on the net can tell you what varieties of tea are lower in caffeine.
5. Use less tea. It takes very little tea to make good KT. You can use 1/2 to 1/3 what is normal tea drinkers strength.
If you use one or more of these suggestions you can reduce the caffeine content to 5% or less of a normal cup of hot tea.
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STARTER POT
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Though not required, a starter pot offers several advantages in helping to maintain a consistent product and healthy balanced culture. You may already have the beginnings of a starter pot if you are storing spare cultures in KT somewhere.
Besides a place for storing spare cultures, starter pots provide the most acidic starter available for fighting mold. They also ensure the bacteria remain fully active while keeping the yeast in check but healthy.
Though it may be counter intuitive, this dissolve-your-dentures, extremely acidic starter actually improves the taste of KT when maintained properly.
A starter pot should hold roughly 5 to 10 times the amount normally used for starter or half to an equal amount of the tea volume you currently brew with. This ensures the bulk of the starter fluid is extremely aged and acidic when drawn to begin fermenting.
Maintainence:
A great way to get your pot started is as a means of salvaging one of those batches that may have soured faster than usual. Similar to continuous brewing, when you get ready to start a new brew you draw the needed starter from the starter pot and replace it with freshly fermented KT.
Only keep one or two spare cultures in the pot and replace them with the newest cultures which aren't currently committed to a ferment. This helps slow down the accumulation of dead debris in the pot. When you remove the older cultures, squeeze out as much of the juice as possible to take advantage of the acid content and free some of the new cells to further boost the bacteria population.
Filter the contents of the starter pot every 4 to 6 weeks to insure dead cells don't accumulate and cause detrimental side effects. When dead cells begin to stack up, the yeast will cannibalize them which can result in some pretty nasty tastes and smells.
Add distilled water to the pot as well, to compensate for any evaporative loss. Feel free to over compensate a little when you do. The bacteria seem to do better when fresh water is added and their health is the main reason for using a starter pot.
Only add fermented tea to the starter pot. This ensures the maximum amount of sucrose has been converted into glucose and fructose. Though not critical, this is fairly important because sucrose will stimulate the yeast where as glucose and fructose will not.This last minor detail is the number one contributor in keeping the culture balanced over successive generations. This is because glucose ensures the culture has fuel for activity without causing the yeast to go into the highly reproductive respiration mode, normally triggered by sucrose. |
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DOUBLING TECHNIQUE
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The doubling technique is simply this:
- Instead of adding all the sugar at one time add 15% the first day, 30% the second and the balance the third day.
This technique is great for helping a sluggish culture. Be forewarned that it is mainly designed to increase yeast activity which is rarely necessary. But if you find the ferment sours slowly and there is little SCOBY growth, this should do the trick unless the culture has been contaminated.
Kombucha normally takes advantage of an effect known to the beverage brewers world as the "Crabtree" effect. Simply stated, when too much glucose is present in the ferment, the yeast slow down and become almost comatose. They cease respiring (and with it reproduction) and switch to fermentation at a rather lethargic pace.Now to some degree this effect is desirable but if your culture is struggling then you can put it on the fast track by gradually adding the sugar over the life of the ferment so that the yeast only convert as much sucrose into glucose as the population can make use of. This will yeild higher rates of reproduction which will be able to consume higher volumes of glucose as it becomes available. |
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DISCLAIMER
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I made this stuff up so if you have any better theories let's hear them. Well OK it's not all fiction. What you have before you is the result of several years of tracking and recording of different KT formulas and techniques coupled with knowledge I gained from the beer and wine brewing experts along with the documented research of KT done by Guenther Frank, Mike Roussin, Norbert Hoffman and Philippe Blanc to name just a few.
If there is anything in this document that contradicts known research you have possession of or can direct me to, I'd like to hear about it.
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Do you have a question or seek a solution to a Kombucha problem not covered here? You can email me with the details of your situation including information about the water, temperature, type and size of brewing vessel or anything else suspected of contributing to the problem.
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