The answer of course is NO. Those crystals in your glass are innocent, and even desirable, but most consumers consider this a panic-inducing problem or wine fault. They are quick to assume that they’ve ingested glass, and granted, they’ll crunch if chewed, just as you imagine glass would. This residue is natural, harmless potassium bitartrate crystals, more commonly known as cream of tartar (yes, the stuff used by bakers). The crystals are the solid, physical evidence of natural acid in wine, acid that ensures wine is balanced, fresh-tasting and colour is preserved. Trouble is, cream of tartar is only partially soluble in liquid, so there lurks the chance that when chilled, the crystals can materialize in wine.
Wine diamonds in the bottom of a bottle.
So how does this substance form?
Ripe grapes are sweet with sugar, but also contain generous amounts of malic and tartaric acid. After fermentation another acid is formed, called lactic acid. These three acids are usually invisible in wine, kept hidden in a dissolved state. It’s the cold that unlocks the crystals, causing them to precipitate out of the wine, dropping to the bottom of the bottle as deposit. Both red, rosé and white wines contain suspended potassium bitartrate, but reds are generally not served chilled, so the residue doesn’t form (unless the red has been stored for a protracted time in a very cool cellar). White and rosé wines of course are stored in a fridge or served in an ice bucket, and the crystals can appear when the last drops are poured. Sometimes the crystals cling to the bottom of the cork; sometimes they appear as white powder.
Diamonds sometimes form on corks.
Wineries pour a great deal of expense, research and effort into the prevention of these crystals, simply because consumers assume them to be dangerous at worst (pieces of glass), or undesirable at best (added sugar crystals). There are several ways of preventing potassium bitartrate deposits, but all methods are energy-inefficient, take time and are costly. The simplest method is called cold stabilization, where the wine is put in a large stainless steel tank, chilled to 0-4 ᵒ C for one to three weeks, then removed (racking, in wine-speak) off the deposit that has crystallized during this cooling. This is expensive, and both flavour and colour can be stripped from wine. Subtle nuance, delicate flavours, terroir expression - all facets of wine that a hard-working winemaker has tried to express in the wine - can be compromised just because of consumer fears. Education is the key. An astute store clerk, restaurant server or sommelier can explain the occurrence of ‘wine diamonds’. Decanting the wine through cheesecloth or coffee filter is an easy fix. Or just let them be.
Note the thick frost former on the outside of these cold stabilization tanks.
So what’s the message in the bottle when you observe crystals?
Nothing harmful – they do not affect the quality of wine, or change the taste.
Your wine has been made with care and minimal intervention
Money and resources have been saved by avoiding tartrate stabilization, and that saves you money too
You are an educated wine-lover and will now look forward to being showered with wine diamonds