When i salt crystals they precipitate are not always accepted by the consumer and the buyer, but we don't have to worry because it is a natural process.
We understand why.
In grapes the Potassium and Tartaric Acid they are present in separate compartments and starting from the crushing they come into contact in the same solution giving rise to supersaturation conditions in the must.
Their concentration is not substantially modified by the activity of yeasts and therefore during the fermentation and storage of wine they give rise to evident phenomena of potassium bitartrate precipitation.
The solid, partially crystalline mass looks like an end precipitate already after the fermentation of the must and the winter storage of the wines.
Why is pH important?
At the pH of the wine, tartaric acid is partially dissociated, i.e. a part of these molecules is stabilized by hydrogen (COOH), while a part is dissociated (COO–) (in this section I will simplify the balances by not considering the double dissociation of tartaric acid).
The dissociated acid being negatively charged will bind to something positively charged, and in wine this bond is formed with the potassium ion (K+) forming potassium bitartrate (COOK) which is not soluble in wine, this means that it will precipitate to the bottom of the bottle or tank.
What are the physical methods to stabilize a wine?
In general, the solubility of all salts is influenced by temperature. In the case of potassium bitartrate, the temperature has a great influence on its solubility: when cold it decreases a lot, and this is the reason for the traditional practice of storing wines, during the winter, in containers kept in rooms with low temperatures, in order to obtain, in spring, stable wines from precipitates and considerably more limpid. The phenomenon is the same that is used for the cold industrial stabilization of wines.
All physical methods of tartaric stabilization are based on the same basic principle: that of bringing the wine to a low temperature for a certain time, at which the precipitation of potassium bitartrate can occur. The crystals that have formed are then removed, separating them from the liquid maintained at the crystallization temperature.
Generally the cellars operate for relaying, for periods varying between 7 and 30 days.
A new method of tartaric stabilization is that performed with electrodialysis. The procedure, authorized since 1997, makes it possible to selectively remove the ions responsible for tartaric precipitations, independently of the presence of colloids that limit the effectiveness of cold stabilization. Electrodialysis allows to treat wines rich in colloids with the absolute certainty of the result.
What are the adjuvants that inhibit precipitation?
Among the protective colloids used practically in the cellar, the most important is metatartaric acid. It is a powerful crystallization inhibitor: a few milligrams per liter (5/10 g / Hl) of metatartaric acid are enough to inhibit crystallization for a period of about 6 months.
In the context of colloidal substances, proteins can greatly influence the precipitation rate of potassium bitartrate.
It is evident that this fact leads to two very different treatments of the wine: on the one hand the complete elimination of the inhibitory colloids present in the wine followed by a cold treatment, on the other hand the maintenance or addition of these colloids, in in order to achieve a total inhibition of precipitation.
Furthermore, the use of CMC (Carboximethylcellulose) is widely used as it strongly inhibits crystallization. The only problem is its use in red wines as it creates instability with the coloring matter. It is NOT allowed for organic wines.
A modern method of tartaric stabilization, which promises to open interesting possibilities, is that which involves the use of mannoproteins extracted from the cell wall of yeasts. At the moment, however, relatively high concentrations of commercial mannoprotein preparations are required and they are the most expensive adjuvants on the market.
We understand that we have the tools to inhibit the process.
But what is really important for the consumer?
And you allow a wine to precipitate?
Hello
Until next time
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