You might be thinking of potassium metabisulphite? [1] Sounds like it's a white powder, which fits your description. Also, I grew up in India, and am pretty su

You might be thinking of potassium metabisulphite? [1] Sounds like it's a white powder, which fits your description. Also, I grew up in India, and am pretty sure that at school, I read about this being introduced to complement traditional preservatives. ---------------------------------------- [1] https://en.wikipedia.org/wiki/Potassium_metabisulfite https://en.wikipedia.org/wiki/Potassium_metabisulfite