More specifically, the pellicle grows in response to the direct contact with oxygen in the air. Usually, this is on the top but if you use a vessel made out of food grade silicone, it will be on all sides because silicone is oxygen permeable! I plan on posting videos about this phenomenon in the near future
Hello John. Thanks so much, your information is absolutely clear and easy to understand. A question remains for me: What about the caffeine content in the tea? I've heard is also quite important for the whole process, possibly being another ingredient of the mix from which the scoby feeds. I hope you can help me clarify this.
Thanks you for your videos on kombucha. There's so much misinofmration about kombucha fermentation on YT! It's so nice to have at leas one science-based channel.
I'd like to ask if you have tested Kombucha for b12, and if so, what is a more common results - rich, plentiful amounts as some labels i have seen present, or negligible, trace, non-livable amounts?
great video ! So how much ethanol left in there? is it all converted to acetic acid? also what happens when acetic acid yields H2O and CO2? if all the acetic acid is converted then why do we still taste sourness?
There will be ethanol left in the kombucha because it is not all converted to organic acids, including acetic acid. Based on the laws of chemical equilibrium, no reaction will progress fully to product. Therefore, all of the acetic acid does not get converted to water and carbon dioxide. That's a good thing because we like the sour taste that kombucha is known to have.
Hi Jack, we use an enzymatic assay to determine sucrose, glucose, and fructose in the sample. These organic acids don't affect the enzymatic assay like they do in a measurement such as %Brix.
Does the brewed tea contribute to the chemistry, or will the SCOBY still produce it's end products if only water and sugar are used? Sugar is always added to the brewed tea to start the fermentation phase. Great series of videos.
Hi, could you explain how the acetic acid is transformed into CO2+H2O ? I noticed that a vinegary Kombucha that sits in a bottle for a long time can decrease slightly in acidity. Could it be the cause ? Cheers from France.
Hi John. Thank you for the video. It's informative and useful. Is there a place you could refer to study all the reactions occurring during the fermentation process?
Thank you so much for the very informative video! I'm curious about one thing, if the main component that starts the fermentation is sugar, then what does tea provide other than its polyphenols as antioxidant? Does fermentation affect the phenolic compounds in tea or does the compounds in tea affect the fermentation or the scoby itself? Thanks in advance!
This is a great question. It is known that the tea provides nutrients necessary for the type of fermentation occurring in kombucha brewing. There has been scientific research that has shown that various components of the tea can affect the fermentation process and ultimately determine parameters such as alcohol content, antioxidant concentration, etc. Looking at specific aspects of this would require digging into the scientific literature more. Maybe a topic for a future video!
Sir, why the store bought Kombucha produced by big brands are more strong and satisfying than local breweries also I noticed that the Kombucha from local small breweries are more sweeter, can you please explain why is that and what is difference between the process they use on bigger scale and smaller scale.
Hi! There are several ways to increase ethanol production in your kombucha. The simplest way is to increase the amount of sugar used as it provides food for the yeast. Another way is to make your fermentation more anaerobic as this inhibits the bacteria from converting the ethanol to acetic acid. Finally, other strains of yeast can be added to enhance alcohol production (e.g., champagne yeast).
John- what are your thought about Jun tea? I’ve read that Kombucha and Jun have diff yeast and bacteria strains which do not cross over or converted over when switching from white sugar to raw honey and green tea.
Thank you John for sharing this knowledge! this is very helpful! Without a background in chemistry, and if I want to know more about the chemical reactions of the brewing process, should I start with a basic chemistry text book? what would be the best way to fast learn about the science behind the brewing process! thank you!
Hi Yinghe! We are so glad that you enjoyed the video and found it useful. Unfortunately, there is not a textbook that summarizes the complex processes of the fermentation of kombucha. A basic chemistry textbook would give you a nice background about how reactions occur and different types of reactions. However, it won't be specific to kombucha.
Thanks for the video! Could you explain the purpose of the second ferment? I have noticed in Kombucha diy videos that the first ferment is usually covered with a fabric and I assume this is aerobic. Perhaps it is the phase where sucrose is converted to fructose and glucose? I assume this is also maybe a slower phase since this stage is normally 1 week long. And then the second ferment involves bottling the Kombucha (creating an anaerobic environment) and then this is the stage where carbon dioxide is produced. But I wonder if carbon dioxide would be produced anyway if you just let it ferment for long enough in the first instance? Or I guess maybe the bottling just allows for the capture of carbon dioxide for the fizziness and has nothing to do with being anaerobic?
The secondary fermentation is usually a flavoring stage that also leads to increased production of carbon dioxide. Carbon dioxide is still being produced in the primary ferment, but in many cases it is escaping when left open to the environment like you noted.
