Tannin powder substitute

[BenHardy]

I'm in the process of making peapod wine, and the recipe calls for a teaspoon of tannin powder. I have run out of that, and have (being English and all) just put in a mug of strong black tea. Though it is now academic, do people know whether this works, and whether I am affecting the taste by doing this?

 

[BobF]

CJJ Berry mentions using tea. I'm not sure about the proportions.

 

[Tom]

Grape skins, raisins will leave some