Troubleshooting Your Wine
The faults and flaws and their analysis and resolution presented below are from my latest book, Modern Home Winemaking, where you can find additional information should you wish to explore these further.
FRIDGE TEST TO DETERMINE TARTRATE STABILITY
The fridge test is a test you can easily implement at home to predict tartrate stability.
Filter about 100 mL of wine down to 0.45 µm using a syringe filter to minimize any potential protective effects of other colloids — this will improve the confidence of the test.
Pour the sample in a glass bottle, cap, place in the coldest spot in the refrigerator, and hold for 7–10 days. Typical fridge temperature is around 4 °C (40 °F), but the test is more effective and shorter if you can chill the sample to around 0 °C (32 °F) or even lower. Just keep in mind that whatever temperature you perform the test at, that’s the temperature you have to chill your batch, and that means having sufficient space in the fridge for your batch or taking advantage of cold weather, or using a glycol chiller to cold stabilize.
At the end of the wait period, take the bottle out, flip it over and hold it up against a bright light to see if any tartrate crystals have formed.
If there are no crystals, the wine is considered tartrate stable to the test temperature (i.e., the temperature in your refrigerator) and requires no further processing against tartrates. Tartrate precipitation may still occur if the wine is stored at colder temperatures than the test temperature. What this means is that if you stabilized your wine in your fridge where the coldest temperature was only 6 °C (43 °F) and you give a bottle to a friend who puts it in his fridge at 4 °C (40 °F) and leaves it there for a week, he/she will likely find tartrates in your wine.
If crystals are visible, then the test is positive, i.e., the wine is not tartrate stable, and therefore it needs to be stabilized.
NOTE: There is a variant of the fridge test — called the freezer test — where a sample is held overnight at much lower temperature in a freezer and not have to wait for a week or more. Since cold stabilization is in practice usually carried out at cold temperatures, perhaps close to freezing but not freezer temperatures, you may get different results cold stabilizing than from the freezer test.