Readings

In this topic, I was introduced to Brewing and Fermentation. Though the readings were quite long, they were interesting as it has allowed me to gain a wider exposure on these two particular aspects.

Brewing

In the Coffee Workshop which I attended a few weeks back, I was introduced briefly to the different parameters of brewing, such as temperature, pressure, grind size, etc. In one of the readings on Brewing, these concepts were further reinforced, where I learnt the parameters of brewing in greater detail.

One interesting thing I came across was that long cup coffees tend to be both stronger and bitter, which is due to over extraction that favors the extraction of less soluble, bitter and astringent compounds. This changes the sensory profile, where it moves from sweet acidic one, to bitter-harsh one. To prevent over extraction, filtration should be stopped after a planned time and hot water can be added to the brew instead of waiting for all the water to pass through the grounds.

Fermentation

To put it simply, fermentation is a biological process carried out by microorganisms, which can transform many raw materials into flavors. Generally, it involves the microbial conversion of glucose (carbohydrate) into ethanol and carbon dioxide.

For a good fermentation process, temperature is important. As temperature increases, fermentation rate accelerates. With increased fermentation rate, aromatic compounds are produced because the metabolic intermediates are excreted from yeast. Warm fermentation often leads to a fruity aroma. However, if the fermentation temperature gets too hot, desirable fruit aromatics will be blown off, and the yeast will become too stress, which inhibits yeast activity. Hence, the optimal temperature for fermentation is usually room temperature!

Fermentation Workshop

In Week 4, I attended a fermentation workshop conducted by Ding Jie, the founder of Starter Culture. I was taught on certain basic concepts regarding fermentation, which mainly focuses on Kombucha. This workshop was definitely enjoyable as I got to do my own Kombucha fermentation!!

So what is Kombucha exactly? Well, kombucha is a fermented, slightly alcoholic, sweetened black or green tea drink. It is consumed because of its supposed health benefits. Specifically, for kombucha fermentation, lactic acid bacteria (LAB) converts sugar to lactic acid, and acetic acid bacteria (AAB) converts sugars to acetic acid and cellulose. Yeast was added to convert sugar to ethanol.

We were provided with both a jar and a bottle to observe for fermentation.

The jar was covered with a kitchen towel (breathable material) to allow aerobic, primary fermentation to take place. This allows oxygen to enter so that fermentation can take place.  A layer of white substance was seen forming on the surface of the tea after 5 days. This layer is known as the cellulose pellicle, which is a bacteria that forms during the fermentation process.

On the other hand, anaerobic, secondary fermentation occurred in the bottle. Carbonation drops were added to make the fermented kombucha fizzy in the airtight bottle. When I first tried the fermented kombucha from the bottle, it tasted sweet and slightly fizzy. After leaving it to stand at room temperature for 5 days, fumes were seen when I opened the bottle, due to build up pressure! Moreover, it tasted much more sour and fizzy.  Having left it longer to allow the brew to continue its fermentation process, the more sour and tart it gets!