Updated November 10, 2025 Beginning in the 1990s, veterinarians began seeing dogs who developed acute kidney failure after eating grapes, raisins, or currants. The cause was a total mystery for decades. But in 2021, tartaric acid (the basis of cream of tartar) was discovered to be the part of grapes that cause them to be toxic to pets. The amount of tartaric acid can vary in grapes by their type, how they were grown, and how ripe they are, which could explain why some pets get very sick while others ...