Tea in the freezer.

Nigel , Thanks for your comments. We, as a lay man, know that tea is hygrospic- it takes moisture from the atmoshphere. And we also know that tea loses its intrinsic quality once the tea has moisture content more than say 6 %. What is the minimum atmospheric humidity, above which , this tea having 6 % moisture will start gaining moisture from the atmosphere. TIA S. M. Changoiwala, Director Gopaldhara Tea Co Pvt Ltd. KOLKOTA INDIA

Comments -

1. I never found any apparent organoleptic change in tea frozen at 6% moisture content and below (this is still pretty dry - crisp between the teeth - tea is regularly traded at around 8% mositure, bug growth begins at 12-14% moisture, green veggies are at 80% plus).
2. Structure alteration is inversely proportional to freezing temperature - hence I specify minus 18 deg C. Liquid nitrogen (minus

Nigel at Teacraft

Excellent question! Teas lose or gain water to the atmosphere driven by their own moisture content (%mc) and the moisture content of the air around them (%RH). In a closed system (like a tea sack) they will soon reach equilibrium ( = ERH - this is also termed water activity Aw, a better way of measuring moisture content but not one that the tea industry has yet embraced). In practical terms (and using the data I have to hand) tea at 3%mc is in equilibrium with air at 5-7%RH and will gain moisture at any humidity above this. This is a very low humidity rarely found in nature hence we consider tea highly hygroscopic because it is normally stored in wetter conditions than this. Moisture sorption is not a straight line against humidity and uptake is particularly rapid between 4 and 8%mc - thus at 5%mc a Darjeeling tea will be in equilibrium at 19% RH, at 7% it equilibrates at 57%RH and at 9%mc at 65%RH. In direct answer to your question (and remember this is influenced by tea type, tea particle size, tea solids content, and temperature) the minimum atmospheric humidity, above which Darjeeling tea having 6% moisture will start gaining moisture from the atmosphere is 48%RH at 20 deg C.

Nigel at Teacraft