It's hard to find tannin powder as there is no wine making supplies in my country. There, I'd rather use raisin as tannin substitute in my wine making process. However, I'm not sure how the conversion of those thing. Anyone could give me some advice? The recipe needs 1/4 tsp of tannin and 1-1/2 tsp of acid blend.
I have always used black tea stewed for about 30-45 min, and used as my about half of my brewing water, if you want to try with raisins have a look here: