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.

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 3.0. 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 acetic acid.

Lemon juice or vinegar has a pH  of about 2.0

Typically apple-cider vinegar is 5 % acetic acid while  Kombucha Tea ~ 1%. The difference between vinegar and kombucha is gluconic acid. The gluconic acid is produced by the same species of bacteria that produces acetic acid. Bacterium gluconicum, Bacterium xylinum, Acetobacter xylinum; xylinoides, and Ketogenum. Cornel University Study found the average kombucha ferment to be slightly less than 1% acetic acid (7 g/L) while still being pleasantly tasting and anti-pathogenic (anti-microbial). The acetic acid is the vinegar taste. The sharpness or kick that most people like in their Kombucha Tea. The gluconic acid smoothes the harshness of the acetic acid. The ratio of gluconic acid to acetic acid is a balance we strive for in a kombucha ferment. Our fermentation method produces about a 2% (1g/L) gluconic acid. The other major component identifying kombucha tea is fructose. (4.8 g/L*)

The yeasts in the Kombucha SCOBY are primarily of the Saccharomycodes ludwigii, s. apiculatus, Schizosaccharomyces pombe, Zygosaccharomyes, and Saccharomyces cerevisiae. 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 bacteria than convert to  acetic acid. Both the yeast and the bacteria 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 is present switching to an anaerobic (without oxygen) ferment. The yeasts also produce carbon dioxide (carbonation) which suffocates/diminishes the bacteria. One effect may be more alcohol present (still less than 1/2 of 1%) but no additional acetic acid created as the bacteria rely upon oxygen. The yeast may be active in temperatures as low as 40F/5C with or without oxygen.

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 first stage of fermentation as outlined above should produce a semi-sweet tasty Kombucha Tea. There should be some sharpness or sourness, not so much as to make it undrinkable, nor too sweet. If you are checking the pH it should be from 2.5 to 3.1.

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