Hello users of the internet! On 7 February 2020, I had attended yet another interesting workshop on the chemistry behind everyday food items. This time, as you might have guessed from the title, is about the fermentation of tea, or what is commonly called, “Kombucha” (no, it does not contain seaweed). The speaker Tan Ding Jie, who had attained his Masters in food science in NUS, had also generously provided us with 2 bottle of kombucha to take home! The one in the wider jar which contains only the culture is drinkable!

What is fermentation

First off, one must know what fermentation is in the cooking world. Fermentation is a biological process carried out by microorganisms which can transform raw materials into flavours. Simply speaking, you add a microbe to a substrate to liberate flavour. It is known that beer is barley (substrate) fermented using yeast (yeast), and yoghurt is milk (substrate) fermented using bacteria (microbe)…but what does Kombucha use? Kombucha is tea fermented using BOTH bacteria and yeast called SCOBY (symbiotic culture of bacteria and yeasts) and both anaerobic and aerobic air exchange occurs. Usually aerobic (in the presence of oxygen) ethanol oxidation to acetate occurs first or , followed by anaerobic (in the absence of oxygen) fermentation.

Factors affecting fermentation

But, what if I want to eat my kimchi as soon as possible? How does one speed up the fermentation process? A wide range of factors affect the speed of fermentation, so I will only go through some of it. For example, yeasts usually grow at pH 4-4.5; a 10 degrees celcius increase in temperature could cause rate of fermentation to double; the water used to ferment is also very crucial. Water treatment plants usually add a certain amount of chlorine into water to kill any harmful bacteria, hence it is no surprise that these chlorine would also kill the bacteria used to ferment the substrate.

However, when trying to be efficient in fermentation, one must also consider the taste of the end-product. A faster ferment would also mean a more superficial flavour since not enough time is given for the flavours to slowly build-up.

Kombucha making

According to Ding Jie, his regular kombucha recipe is 1% tea, 7% sugar, 10% starter culture and the rest is water. Starter cultures are the microorganisms added to kick-start the fermentation process, but cannot be added directly into hot water/tea. The heat would cause the culture to get killed hence, we must cool the tea fast before adding the starter culture. We were also instructed to ferment the kombucha in the jar for 5-7days, inserting a paper towel before capping to ensure some aeration. A top layer of cellulose pellicle had formed after 5 days, as shown from the picture below. Ding Jie had confirmed that the layer could either be discarded or eaten. However, should there be mould, it has to be thrown away!

Microbiomes link your gut to your brain

Firstly, kombucha is fermented tea, which means it has both the benefits of tea and fermented foods. As such, kombucha contains antioxidants similarly to tea, but also contains probiotics. Our body, especially the gut, contains many friendly microbiomes(bacteria) that helps digest food and provide us with nutrients. Every body contains different amounts of microbiomes, but everybody faces stress everyday. Research has shown that stress does indeed alter the gut’s microbiomes, which is why health problems(especially surrounding the digestive tract and gut) always arise during stressful times.

There has been an ongoing research study about the “gut-brain axis” or more specifically the “microbiome-gut-brain axis”. Not only is there a link between the gut microbiome and sleep, mood disorders and anxiety, but 70% of people with autism also suffer from gastrointestinal problems. This is a very current research topic and scientists are funded millions of dollars to try and provide evidence for the relationship.