TLDR: Should you retain the biofilm? #

It isn’t required, but it won’t hurt anything.

What is the biofilm? #

Sometimes called the pellicle or the SCOBY, the biofilm is one of the things that really make kombucha stand out. It is the rubbery disk that develops during fermentation. Some are adamant that it must be kept from batch to batch, going so far as to wash and cut it down.

The biofilm is created by the bacteria in the kombucha as a defense mechanism against harsh environments. It is very pure cellulose which scaffolds together bacteria and yeast, providing a physical barrier to the outside world. In the wild, this would protect the bacteria from harsh environmental changes such as temperature swings or harmful UV light.

When fermenting in our controlled environments the protective value of the biofilm is less meaningful. We keep the fermenter out of the light and keep it at a temperature the bacteria like. The fermenter is covered by a cloth from direct access, preventing bugs or other airborne baddies from invading the culture.

Why keep it? #

It is an undeniable fact that the biofilm is chock full of the good microbes that make kombucha what it is. It is literally bacteria and yeast glued together into a solid mass. If you choose to keep the biofilm between batches it will absolutely contribute more microbes to your next batch.

However, the liquid is quite plentiful in these microbes as well. This is where the probiotic benefits claimed by kombucha originate. So while the biofilm will mean more microbes starting your new batch, the liquid has enough already to jump start a healthy fermentation.

What to do? #

In the end, like so many things in life, it is up to you! I usually throw out the biofilm between batches simply because I don’t want to spend any energy keeping track of it. I have had great success brewing without the biofilm.

If you like the mystery of that strange disk floating in the jar or if you want to give your batch the absolute best environment to start your next batch, go ahead and toss that thing in. However, the ratio of starter to tea is probably the best way to hedge the bet in your favor if you are nervous about keeping your culture going.