danielpflood.Chemistry.Health.Types of tea
From: Tea Oxidation >>
How is oxidation stopped?
There are two things that can be done to halt oxidation: 1) denature oxidation enzymes or 2) displace oxygen.
1) Denaturing the oxidation enzymes entails treating raw tea leaves with heat. This occurs in two different stages: the “enzyme kill” stage and the “final firing” (drying). The earlier stage, “enzyme kill”, is a high heat quick process lasting under one minute. This can be done by steaming, pan-frying (tossing in a wok), or by baking the leaves. The later stage, “final firing”, is done only by baking the leaves for about 20-60 min with the goal of reducing water content in the leaves to 3-5%.
The use of heat during the final firing step actually results in an initial rise in enzymatic activity where 10-15% of theaflavins will form in the first 10 minutes.3
2) The second way to halt oxidation is to remove oxygen. This is mainly the issue for the storage of tea. I strongly recommend storing tea in an air-tight and light proof container will minimize the opportunity for passive oxidation. This is why Eli Tea tea’s are sold in tins.
In the tea trade, wholesalers of tea usually package tea in vacuum sealed, nitrogen enriched bags. Sealing bags with nitrogen would displace and or diffuse any oxygen from reacting with the tea. These stringent measures for preservation increase shelf life of the tea to up to ten years, compared to tea simply sealed in an airtight container, which has a shelf life of 6-24 months.
Continuing on the topic of nitrogen, Japanese researchers in 1987 developed a new technique for the “enzyme kill stage” where the tea was given a nitrogen treatment instead of the traditional heat treatment methods. Treating the tea with nitrogen increased gamma aminobutyric acid and therefore these teas have adopted the acronym suffix of GABA. (i.e. GABA oolong, GABA green etc.) GABA can be naturally found in the brain and functions as neurotransmitter.