Tartaric acid is a small 4 carbon dicarboxylic acid, with the 2 middle carbons hydroxylated (2,3-Dihydroxybutanedioic acid). The precipitated potassium salt sediment has been known to winemakers since ancient times. It can cause an unwanted gritty texture in grape jelly, but this rarely happens now with modern processing methods. In grape juice drinks and wine, the crystalline sediment may be mistaken for broken glass. Chemically, they are not toxic at all. Below are photos from a few incidents.
Latest incident. Weight of the largest crystal was 13 mg.
Illuminated from above and below, comparisons
The biggest one is nearly 1/4 inch in length. It was not known how long the bottle had been opened before the customer noticed the precipitated crystals.
A different incident: Pyramid shaped crystals (bipyramids connected base-to-base
Based on crystal shape and the ingredient list, these are probably calcium tartrate. In those years the lab no longer had an IR spectrophotometer and I couldn’t use AA or ICP to measure % calcium and potassium for conclusive ID.
Dan Harring (54) 