A stable wine is one for which, under normal storage conditions, there will be no change physically or sensorially in the time between bottling and drinking. This includes visual changes as well as those in mouthfeel, taste, and aroma. Through testing and trialing, we do our best to protect a wine’s stability for a reasonable duration—but because it is impossible to know when someone will open a bottle, there is potential for some old wines to be quite changed upon opening, compared to when they were bottled.
The five areas of stability are oxidative, color, metal, protein, and tartrate. Protein stability is frequently referred to as heat stability; and when a wine is tartrate stable it is also known as cold stable. Our main focus today will be on this last type, cold stability.
The practice of ensuring a wine is cold stable is pretty simple: once blending is complete, the wine should be “crashed” to a temperature of at least 39ºF for a minimum of four days. The walls and floor of the cold tank become coated in spiky, crystalized tartrates that have precipitated out of the wine and stuck to the steel.
The main components of this precipitate are potassium and calcium ions (KHT, potassium bitartrate, and CaT, calcium tartrate) which originated in the fruit during the growing season. This can indicate levels of potassium and calcium in the soil, water, and other aspects of the vineyard environment. Holding the wine in a cold state for an extended period is the best way to remove these compounds because their solubility decreases as temperature does—deeper cold means more precipitate fallout.
With hot water and elbow grease, this disposable material is washed down the drain, the tank is sanitized, and another wine is transferred in to begin its stabilization process.
Our practice at Merry is a bit more extreme than the mandatory: we hold the wine in an environment of 29-31ºF for two weeks before moving it to a new vessel. We only do this with white and rosé wines, because we don’t expect our red wines will ever be chilled deeply or for long enough to result in a tartrate precipitate in the bottle. Crystal formation of the tartrates can also be inhibited by other components such as protein, polysaccharides, and tannin. These high molecular weight compounds are usually more present in red wine, which is another reason why we don’t worry too much about them being cold stable.
Rosé usually goes into stabilization first since we don’t blend it with anything else—the blend of Mourvèdre and Syrah that we get on harvest day is what we put into the bottle! For the rest of the whites, though, the temp can’t be turned down on the first one until all four are blended in their final form. This year the last cold stable wine intended for bottling will be finished at the end of March, so we have a ways to go! We expect to release the first whites of our 2022 vintage in the late spring…the anticipation is building!
