Tea manufacture and Aspergillus

Submitted by Aspergillus Administrator on 23 July 2008

How tea works

Tea is the most widely drunk beverage in the world (Wiki) with over 3 million tonnes produced per year.
Many different types or grades are produced and I was intrigued to read this article which states:

Poria Cocos Brick (Fu Tea) is the top grade in the ancient kind of brown tea. Being complete ferment tea, Poria Cocos Brick Tea is the most complex and unique brown tea which has the longest production processing cycle. It products Aspergillus Cristatus, brick-like in appearance, with flourishing golden flowers all over, dark and shining, red and strong tea soup, mellow to the taste with lasting scent.

Not making much sense but clearly indicating that Aspergillus is involved in the manufacture of this tea I decided to do a bit more research.

Some teas are fermented using enymes or crude extracts of fungi and Aspergillus is one of the best producers of those enzymes. This patent goes into this in much more detail:

“In fermentation, a microorganism (mold) is preferably co-present, in order to sufficiently obtain the flavor and physiological activity specific to fermented tea. An example of the microorganism that is used is mold. The mold that is used can be present in nature and examples are molds of Aspergillus sp. including Aspergillus awamori, Aspergillus saitoi, Aspergillus niger and Aspergillus orizae, Rhizopus sp. including Rhizopus delemar and also, other molds for processing food such as tempeh mold. From the viewpoint of exhibiting physiological activity, mold of Aspergillus sp. and Rhizopus sp. are preferably used. The type of mold that is used can be one type or a mixture of several types, but pure fermentation using one type of mold is preferable.”

I was then intrigued as to how the mold is added to the tea, and where it comes from:

“Examples of the method of applying the mold to tea leaves and tea leave stems are the method of dry mixing tea leaves, tea leave stems and sporules of the mold as they are, the method of diluting the sporules of the mold by dry mixing together with a food diluent such as wheat flour, rice powder and barley flour and then mixing with tea leaves and tea leave stems, and the method of preparing a suspension of the sporules of mold in saline and then spraying onto the tea leaves and tea leave stems. The amount of mold is preferably 0.001 to 1 % by weight, more preferably 0.01 to 0.5 % by weight, based on the total amount of tea leaves and tea leave stems. When the amount of mold is less than 0.001 % by weight, fermentation tends to be insufficient. When the amount of mold is more than 1 % by weight, production costs tend to become too high.

These strains are easily available, as commercially available mold species such as koji for sake, koji for sweet sake, koji for shochu and koji for tempeh, and also, the fermented tea leaves can be left and reused as a mold starter.

Subsequently, the tea leaves and tea leave stems to which the mold is applied are spread on a bed in the fermenting chamber and then fermented. The temperature of the fermented substance when fermenting is preferably raised to 32°C or higher, more preferably 32 to 45°C, further preferably 35 to 42°C, within 25 hours after beginning fermentation. When such conditions are not satisfied, that is the temperature is not raised to a high temperature in short period of time, progression of fermentation tends to be insufficient. This temperature is preferably maintained for at least 5 hours, more preferably 5 to 100 hours, further preferably 5 to 10 hours.”

So the use of Aspergillus is vital to the final taste and caffeine content of some fine teas. This is another example of the historical and ancient uses of Aspergillus to produce foods in the far east – more good uses for this mold with a bad image!

It is worth noting that most tea is NOT prepared using molds so readers worried about eating foods derived from molds can rest easy with their usual tea bags. Most tea is prepared by crushing, oxidising and drying.

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