Tartrate crystals are a common occurrence in grape products
Hard, crystalline shards or granules are often found in home canned grape juice, syrups and jellies. These formations are the result of tartaric acid, a naturally occurring compound in grapes, reacting with potassium. The reaction forms potassium bitartrate crystals, also known as tartrate crystals. (Sugar and evaporation can also cause crystals, a topic for another article.)
Tartrate crystals are not harmful, but crunchy crystals in your grape juice or jelly are certainly not desirable. Fortunately, there is a method to help prevent tartrate crystals from ending up in your grape products. It’s easy to do, but it does require quite a bit of waiting time, so be sure to plan ahead.
How to prevent tartrate crystals from forming
After extracting the juice from your grapes, allow it to stand, undisturbed, in the refrigerator at least overnight, and preferably 24 to 48 hours. In fact, the longer the better; Oregon State University recommends 2 to 5 days.
When ready to preserve the juice, remove it from the refrigerator, taking care not to disturb the sediment that has settled at the bottom of the container. Transfer the juice into a clean container, carefully pouring it through a strainer such as a jelly bag, flour sack towel, several layers of cheesecloth, paper coffee filter, etc. Be sure to avoid transferring any crystals or sediment into the new container. If desired, repeat the straining process a second time.
For further information on preserving visit the National Center for Home Food Preservation
(NCHFP) at https://nchfp.uga.edu or contact your local Cooperative Extension office.
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Brought to you by the UCCE Master Food Preservers of El Dorado County
Last revised July 2025