Calcium precipitation: an increasingly common defect in wines.

The quality of wine is not only related to its organoleptic characteristics of aroma and taste, but also to its visual appearance. The final product should not be cloudy or contain solids that are deposited or suspended in the air.

Tartaric precipitation is a phenomenon that occurs naturally in wine; however, if it appears in bottled wine, it is mistakenly associated with a lack of quality in that wine by the consumer.

Calcium is absorbed by the plant when it is " stressed," and as a result of climate change , calcium precipitation is increasing.

This is a new phenomenon resulting from increased pH, later harvesting, and the use of potassium polyaspartate for tartaric stabilization.

The warm harvests of recent years have favored an increase in calcium concentration in wines. Furthermore, the higher the pH, the more unstable the calcium is, which is why an increase in calcium precipitation has been recorded.

Calcium tartrate causes white haze in white and rosé wines if the wines are not stabilized and subjected to low temperatures in the bottle. In red wines, it resembles tartar crystals, but the deposit is lighter.

Like potassium bitartrate or any other bottled deposit, this disorder is not popular with consumers and should be avoided at all costs.

Warm years favor greater ripening in grapes with lower malic acid levels and, on the other hand, increase calcium content.

Unlike tartaric stability, which is assessed with the cold test, evaluating the risk of calcium precipitation requires measuring it in wines. There is a risk if the concentration exceeds 60 mg/L in red wines and 80 mg/L in white and rosé wines.

Often, tartaric precipitation also leads to calcium precipitation.

Solutions:

There are several possible ways to treat tartaric instability, including extraction techniques (cold, ion exchange resins and electrodialysis) and the application of protective colloids (metatartaric acid, gum arabic, mannoproteins and sodium carboxymethylcellulose).

For mild instability , a transition to negative cold before application (with or without potassium bitartrate) may be sufficient.

It is recommended to add a calcium tartrate, such as Calcistat 2.0, to wines at a temperature of 10 to 15°C, with fortnightly pump-overs.

Another solution is the use of a mixture of micronized calcium tartrate and cream of tartar, such as Duostab, which allows the crystallization of both tartaric salts (potassium and sodium) in a single step. In this case, the wine should be cooled between -2 and 4°C for two to five days, depending on the volumes to be processed.

We can also apply physical techniques such as electrodialysis or ion exchange resins, but they are expensive and, although they work well with potassium, not always with calcium in red wines.

The use of CMC for tartaric stabilization is very effective in removing potassium in the form of potassium tartrate, but it has no effect on calcium. We can assume that in the absence of potassium, tartaric acid reacts with calcium causing these calcium precipitations.

In wines with high tartaric instability, associated with high levels of potassium and tartaric acid, the use of CMC can be advantageous. The CMC molecule has a negative charge at the pH of the wine and, therefore, interacts with the electropositive surface of potassium bitartrate (THK) crystals, where potassium ions are accumulated, inhibiting their growth.

However, even in wines that were previously stable in terms of protein content, it is important to retest protein stability after the application of CMC, since some wines exhibit a significant interaction between CMC and proteins, making them unstable again, which may require clarification with bentonite to reduce the protein content.

Early bottling is another risk factor, as the wines are deprived of the winter cold which eliminates potassium and calcium through crystallization.

It is recommended to analyze the calcium content before bottling and to take into account the pH and alcohol content to decide on the need for treatment.

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WRITTEN BY:

Pedro Fernandes

Pedro Fernandes is a Portuguese winemaker who has been involved in viticulture since he was 11 years old, where he started making his first wines with his father and doing tasks such as pruning.

Since then he has never stopped and in 2018 he decided to dedicate himself to the wine sector, starting by doing "everything backwards". He began by taking wine specialization courses such as WSET (Direct Wine) and Wine Expertise (ISAG) in 2018/2019. Then he graduated from the University of Nebrijia in Madrid, obtaining an MBA in Oenology (2020). In 2021, at the age of 39, he decided to pursue a Bachelor's degree in Oenology (UTAD), and against all odds, he finished the course in 2024.

Along the way, he created his first personal wine brand - Chãos - and completed an internship at the prestigious Chateau Latour (in Bordeaux).

Currently, he works as a consultant in the wine sector, where he plays a role not only as an oenologist, but also in creating business strategies for wine producers, with a current vision of the market, which includes resources from Digital Marketing and Wine Tourism.