Potassium is the most abundant cation in wine. Its concentration depends both on the grape variety, the soil conditions, the collection procedures (presence of scratches) and the methods used in winemaking. High values of potassium in the grapes will lead to more basic musts, which could adversely affect the quality of the wine. Although most of the potassium salts are soluble, potassium bitartrate decreases its solubility as the concentration of alcohol increases, giving rise to precipitates that, although they do not affect the organoleptic properties of the wine, can be perceived as a decrease in quality.
The iron is present in the grapes from both the same grape and from dirt and from contact with the tools used during the elaboration process. Iron is capable of forming complex colored salts and is therefore a critical element when it comes to providing wine with a hue. An excess of iron, in addition to providing a bluish hue, can cause the appearance of ferric phosphate (white) and ferric tanate (blue) precipitates under oxidation conditions.
The presence of copper in wine is common due to both the phytosanitary treatments carried out on the grapes, as well as the controlled addition of copper salts as part of the winemaking process. Most of the copper is precipitated in the form of sulphides and subsequently filtered. However, a high residual concentration thereof is toxic and can severely affect the alcoholic fermentation process, accelerate phenolic oxidation, cause turbidity and produce precipitates in reducing media. The control of copper concentration is essential to ensure both stability during the ripening process and ensure safe consumption.
Calcium is a natural element in the must, although in certain manufacturing processes calcium salts (calcium carbonate for acidity reduction) and other calcium-rich substances (casein for clarification) can be added. The solubility of calcium decreases with increasing alcohol content, easily reaching supersaturation. In these cases there is a risk of causing calcium tartrate precipitates (and in some cases calcium oxalate) during aging inside the bottle, since its formation is very slow. This problem is particularly relevant in white wines because of its visibility. The control of calcium levels makes it possible to force the precipitation of said crystals, and their subsequent filtration, as part of the manufacturing process.