What's That Stuff In My Wine?

We have been into wine brewing for a few years now but seem to have the same problem every year. Our homemade wine instructions say to let the wine sit for about a year before we bottle it. It is beautifully clear and wonderful tasting. It is a medium sweet grape wine. We get our juice from a local winery. Our problem is when the wine is chilled it gets what I would call residual sugar in it. We have to use a topper with a filter on it to enjoy the wine. Would like to know if you have any opinions on why the wine does this and how we can prevent it.
Thank you
Barbara and Danny
Dear Barbara and Danny,
What you are seeing at the bottom of the wine bottles is not sugar. It is tartaric acid crystals. Tartaric acid is one of many acids found naturally in fruits. Tartaric is the primary fruit acid in grapes.
Essentially, what is happening is your wine has more tartaric acid than it can hold. As the wine gets colder, its capacity for tartaric acid even becomes less. The excess tartaric acid that can’t remain solvent is deposited as little crystals, just like those you are seeing.
This is a fairly common problem when making wine from fresh grapes. It is mentioned in the book, First Steps In Winemaking. You can also read the article, Maintaining Temperature Stability In Your Wines, that is on our website. It will show you how to deal with this issue and how to prevent it in the future.
Best Wishes,
Customer Service at E. C. Kraus
Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.