On Jun 5, 7:11 pm, juliantai > wrote:
> The 15% catechins content is for fresh leaf, which in percentage term
> will be lower compared to dried tea extract. Harold Graham in his
> paper Green Tea composition (1992) quoted a range of 16% to 30% for
> fresh tea leaves, and 30% tp 40% for extract solids. So yes, the
> catechins look low, but is still within a reasonable range.
>
> Are your figures for fresh leaves or dried tea extract?
>

Julian, my figures are in % dry weight of oven dried fresh leaf -
standard science methodology. Hal Graham, as a scientist, quotes in %
dw of fresh leaf (this data came from the bushes at the TJ Lipton Tea
Farm in Charleston, SC) and, as former President of TJ Lipton, quotes
for steeped tea beverage in the cup (in wt % of extract solids).
Differential solubility in hot water leads to all sorts of problems in
correlation between the two systems - for example he gives 3.5%
methylxanthines (caffeine) on whole leaf basis but 7-9%
methylxanthines on an extracted green tea beverage basis - and even
higher at 8-11% for an extracted black tea beverage - that's up to 11%
of the solids in your Yellow Label tea is caffeine; fortunately its
11% of just 0.3 to 0.35% extract concentration in the cup (from Hal's
data) - a more reasonable 100 mg caffeine in a large mug (my
calculation). Similarly with catechins at 16-30% by dw in the field
but reaching 30-42% by dw in the cup. Beverage preparation method has
an over riding effect on what can be extracted and how much (tell me
what figure you want and I will devise a method to provide it) - so
science uses the absolute % dw of fresh leaf method. Hal himself
admits of the beverage preparation method "little is known about the
ability of a normal hot aqueous infusion to extract some of the
compounds recently reported in dried green tea leaf"

Nigel at Teacraft