Last week, we had DJ Tan from Starter Culture to tell us more about Fermentation and more specifically, Kombucha Fermentation!
Firstly, DJ explained that fermentation is a biological process in which microorganisms transforms raw materials into flavours. Such microorganisms include bacteria and yeasts. For example, certain yogurt drinks like Yakult contain lactic acid bacteria (LAB) which are facultative anaerobes. Facultative anaerobes are organisms that can produce ATP in the presence of oxygen through aerobic respiration, and in the absence of oxygen, can switch to fermentation/ anaerobic respiration. In contrast, kombucha contains acetic acid bacteria (AAB), which are obligate aerobes that are unable to survive in the presence of oxygen.
Kombucha is a fermented tea drink. It uses a mixed-culture as its base — “symbiotic culture of bacteria and yeasts” or “SCOBY”. The products of the culture include alcohol and acetic acid from yeast and AAB respectively. DJ also explained that the typical alcohol content of kombucha is low (~0.5%), due to the presence of AAB, which converts the produced ethanol to acetic acid. The fermentation of kombucha is a two-stage process, from an aerobic stage to an anaerobic stage.
There are various factors affecting fermentation, and can be classified into intrinsic and extrinsic factors. Some intrinsic factors include acidity (pH– most yeasts prefer neutral or slightly acidic pH of 5-6) and nutrient content (carbon and nitrogen sources) while some extrinsic factors include temperature and gaseous exchange. It was interesting to learn that a 10 degrees Celsius increase in temperature doubles the rate of fermentation, explaining why flavour development of kombucha the fridge will be slower than that in room temperature. There is also differences between fermentation and spoilage. DJ defined fermentation as deliberate, desired, innocuous and palatable, while spoilage is uncontrolled, unwanted, unsafe and unpleasant. This reminded me of the YouTube Channel Bon Appetit, where they have a show called “It’s Alive” by Brad Leone. Brad mentioned that fermentation is essentially controlled rot, and I found it to be an interesting way of describing what fermentation is.
It then came to the exciting hands-on part of the workshop, where we learn about the practical aspects of kombucha-making, and get to experience it ourselves. To make kombucha, 4 simple ingredients are needed: Tea, sugar, starter culture and water. Firstly, a sweet tea must first be brewed and cooled to room temperature. DJ suggested a ratio of 1% tea to 7% sugar for beginners like us, and encouraged us to manipulate this ratio if we were interested to continue making kombucha at home. Then, 10 -20% of starter per weight/volume of total kombucha should be added before fermentation can begin.
We added brewed, cooled sweet tea to the halfway mark of the jar. We were instructed to cover the jar with a breathable material such as a paper towel to encourage the exchange of air, while minimising external microbes and pests from entering.
The picture above was the same jar on the third day of fermentation. As you can see, a layer of off white, spongey substance is formed on the top of the kombucha. This spongey material is known as the cellulose pellicle, which is a result of AAB converting sugars into cellulose. Some may wrongly identify it as mould, hence DJ showed us certain examples of actual mould growth, so that we would be better aware of when the kombucha has become unsafe to drink. He also mentioned that it is both interesting and helpful to understand how mould grows, as it will also allow us to be more conscious of how to avoid mould growth. The jar was to be fermented for 5-7 days, and it can be used as a starter after a week, to make more kombucha.
The bottle on the other hand, contained kombucha in anaerobic secondary fermentation (it’s essentially what we will get after fermenting the jar of kombucha for a week). At the secondary stage, the kombucha is bottled and more sugar and juice is added for flavouring. We added a sugar tablet to the bottle to promote carbonation.
For both containers, DJ mentioned that they are ready to drink at any time, as it all depends on our preference. I tasted both on the first day, and then on the third day, and it was surprising how much changes can occur in three days. Apart from appearance (both formed cellulose pellicle), the tastes and textures of the kombuchas changed greatly. Initially, the kombucha in the jar is essentially sweet tea, but after 3 days it became a tart, slightly fizzy tea. The kombucha in the bottle initially tasted tart, and after 3 days, I got a surprise when I opened the bottle as the gas quickly escaped onto my face! Expectedly, its contents was very fizzy as compared to when it was first given to us. I felt that both containers tasted like apple cider vinegar, with different degrees of acidity and fizzy-ness. It was an interesting flavour and I do understand why it could be an acquired taste for some. In my case, I’ll be honest and say that it’s not really my cup of tea.. Oops!
As a wrap up of the workshop, DJ presented various applications of fermentation in our daily food, such as yogurt, kimchi, fishsauce etc. He mentioned the variability of fermentation, and how fermentation can be done in various creative ways to enhance flavours or even create new flavours in our foods. I will definitely be continuing to observe and taste the changes in my kombucha!
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