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.
TARTRATES
DESCRIPTION
Tartrates are potassium bitartrate crystals (also known as cream of tartar and wine diamonds), the result of tartaric acid and potassium interacting in wine and precipitating when subjected to cold temperatures. Often referred to as wine diamonds, tartrates are considered by some wine connoisseurs as a sign of good winemaking — it is not!
The crystals look like little tiny shards of broken glass and which precipitate to the bottom of the bottle — some might stick to the side of carboys and tanks — or stick to the exposed surface of the cork in bottles stored horizontally. A small amount is usually acceptable in reds, but an unsightly distraction in whites and rosés, particularly if poured into the glass during service. The problem is only visual with the odor and flavor of the wine unaffected. If you discover tartrate crystals in a long-cellared bottle of red wine, you can decant it through a small stainless steel strainer to avoid unsightly crystals in the wine you pour for guests.
CAUSES
Tartrates are due to no or incomplete cold stabilization. The extent of crystal formation depends primarily on the cold stabilization temperature, and tartaric acid and potassium concentrations, and to a smaller extent on the amounts of ethanol, polyphenols, proteins and polysaccharides.
ASSESSMENT
Making a definitive assessment on tartrate stability is tricky, and definitely not an exact science. And the only practical method for home winemakers is a fridge test.
If a fridge test is positive, you will need to cold stabilize the batch or add a protective colloid.
If crystals formed in the bottle, you will need to treat the wine to stabilize against tartrates.
REMEDIAL ACTIONS
If the fridge test is positive, cold stabilize the batch or add a protective colloid, either metatartaric acid, carboxymethyl cellulose in conjunction with some gum arabic, or polyaspartate.
If crystals formed in the bottle, pour all bottles back into a carboy or suitable vessel, then cold stabilize the batch or add a protective colloid, and re-bottle the wine.
PREVENTIVE ACTIONS
To prevent tartrates in bottles, perform a fridge test and cold stabilize if positive, or add a protective colloid. This stabilization procedure should be performed after any fining procedure to ensure that the addition of a fining agent after cold stabilization does not alter that stability.
Cold stabilize at the coldest temperature possible, around 0 °C (32 °F) or lower, for 2–3 weeks.
There are three important points worth repeating here to minimize the risk of tartrates forming in bottles:
1.
2.
3.
Do not add anything (e.g., bentonite) or perform adjustments (e.g., acidification with tartaric acid) after cold stabilization.