Second Stage Fermenting

Kombucha Mushroom Tea

Secondary Fermentation & Bottling Tips

by Ed Kasper LAc. Acupuncturist, Herbalist, & Homeotoxicologist

One big advantage of a secondary fermentation is that it reduces the sugar without sacrificing the taste. Most folks do a Second Stage to increase carbonation. But be aware this will also increase the alcohol content as well. The aerobic kombucha ferment results in only about 0.5% alcohol, but with an anaerobic ferment and anaerobic yeasts the bottled kombucha goes up to around 2% alcohol. (beer is around 4%, and wine 7%)  

Since brewing kombucha and studying its character I have run across many "correct preparations" and "original methods" therefore first I want to describe the  basic Kombucha Tea brewing guidelines as I understand them.

Kombucha tea should be fermented to a pH of 2.5 to 3.5. While a lacto-ferment the ph should be between 3.6 and 3.9. (a pH below 3.6 may result in the demise of many of their beneficial microorganisms associated with a lacto-ferment.) Lactic acid and the polysaccharide and minerals are expected to keep lacto ferments safe, while aceto-ferments rely upon the acetic acid. Note not all kombucha ferments have lactic acid, therefore this discussion will center around  the Glucoetobacter xylinum responsible for the production of acetic and gluconic acid

Lemon juice or vinegar has a pH  of about 2.0

The yeasts in the Kombucha SCOBY are primarily of the aerobic yeasts; Saccharomycodes ludwigii, s. apiculatus, Schizosaccharomyces pombe, Zygosaccharomyes, while anerobic yeasts like  Saccharomyces cerevisiae, found in bread, beers, wines and other ferments abound in the air and therefore also typically present . This combination of bacteria and yeasts work in an oxygen environment. What is referred to here as an aerobic fermentation. Over-simplified the yeasts cleave the sugar into glucose and fructose. The yeasts produce alcohol from the glucose which the gluconacebacter than convert to  acetic acid. Both the yeast and the gluconacebacter compete for the glucose which the bacteria convert to gluconic acid. In the typical kombucha ferment (9 days at 80F/26C) very little alcohol remains (less than 1/2 of 1%). The Kombucha Tea has gone from really sweet to a pleasant semi-sweet state.

*It is had to accurately know how much sugar or fructose remains. Cornell Study indicated 5% (4.8 g/L) glucose after their typical 9 day ferment (pH 2.5). Their initial sugar start was 100 g/L.

Now if we wish to bottle and refrigerate our brew will stay pretty much as it is with a slight more mellowness. [Cold Stabilization]. To maintain this character we simply have to bottle without leaving any air space. The bacteria will continue to convert the alcohol to acetic acid (becoming increasingly more sour) and compete with the yeasts for the remaining glucose as long as there is oxygen in the bottle and temperatures are in the range of 70F-85F.  The yeasts will remain active as long as glucose and oxygen is present. Anerobic yeasts switch to an anaerobic (without oxygen) ferment when oygen is no longer available and temperatures are above 40F / 5C. The yeasts also produce carbon dioxide (carbonation) which suffocates/diminishes the bacteria. One effect may be more alcohol  but no additional gluconic acid will be created as the gluconacebacter rely upon oxygen. Yeast may produce addiotnal acetic acid. lactobacteillius if present will continue to produce lactic acid, acetic acid and alcohol as well as some carbonation.

Now to the Second Stage Fermentation

The efforts here are to reduce the sugar content creating a 'drier" Kombucha Tea.

Another reason is to reduce the sugar content as much as possible for diabetic and other health concerns like Candidasis.

The Second Stage is an anaerobic (without oxygen) ferment

If your ferment is already pretty much vinegar - its too late. Use it as a hair rinse, foot bath, or a body wash for pets and animals. Or mix with sparkling water or fruit juice and drink.

Now find a nice clean glass bottle and an air-lock. An Air-Lock,  available from your local Beer and Wine Hobby Shop, or from us, have several designs. This simple device protects ferments from infection while allowing carbon dioxide gas to freely escape the fermentation vessel. Water is placed in the air lock and gas is released as pressure builds up. Or you could simply place a balloon over the opening (as pictured below) and use tape to secure. With the airlock you determine when the fermentation is complete by the numbers of bubbles (or lack of bubbles) that flow through. With the balloon its largely a guess and hopefully before the balloon pops.

The warmer the ferment the faster the fermentation.

Bubbles or gas will continue to be produced as long as there is fermentable sugar available.

The acid level (gluconic and acetic) will stay at about the same level since the oxygen supply is cut off and the taste will become "drier" as the sugar is converted to alcohol.

If your desire is to create a higher alcohol content a la Kombucha Wine add additional sugar (glucose or dextrose) just prior to the air lock or balloon or fruit syrups for flavoring to increase the alcohol potential. Some more sweetness to the brew as all the sugar will not be utilized by the yeasts will also be likely. Adding fructose at this point will mainly increase the sweetness without adding additional fermentation or potential alcohol.

Adding Champaign yeasts that  produce higher levels of alcohol is another option. You can choose the yeasts for many reasons besides alcohol production, potential produce 5-12% alcohol. There's taste a factor as well in the selection of additional yeasts.

One final option for those desiring to reduce both the sugar and alcohol content is (besides not adding any extra sugar or fruit) is after the Second Stage ferment is to pasteurize the brew. Heat the brew to at least 140 F to 160 F for 10-20 minutes. This will reduce the alcohol as well as the probiotic population but remain still a healthy and tasteful brew. The lower temperature the less the taste is affected.

You can enjoy and drink away, bottle for latter or further clarify and refine your ferment.

see  How To safely make Kombucha Tea.

In our opinion the safest, easiest and best way to make great Kombucha Tea is the Continuous Brewing Method