In the early 1800s a sir Francis John Davis traveled in China disguised as a Mandarin. He discovered that green teas prepared for export were adulterated with tumeric, prussian blue, and gypsum to give them a richer green color.
… At each pan stood a workman stirring
the tea rapidly round with his hand, having previ-
ously added a small quantity of turmeric in powder,
which of course gave the leaves a yellowish or
orange tinge ; but they were still to be made green.
For this purpose some lumps of a fine blue were
produced, together with a white substance in pow-
der, which, from the names given to them by the
workmen, as well as their appearance, were known
at once to be prussian blue and gypsum. These were
triturated finely together witha small pestle, in such
proportion as reduced the dark colour of the blue
to a light shade; and a quantity equal to a small
teaspoonful of the powder being added to the yel-
lowish leaves, these were stirred as before over the
fire, until the tea had taken the fine bloom colour of
Hyson, with very much the same scent.
…
If the tea has not highly deleterious
qualities, it can only be in consequence of the
colouring matter existing in a small proportion to
the leaf; …
It is possible that the Chinese didn’t know that prussian blue is a poison. It’s also possible that they were using real tumeric!
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