Winemaking Techniques: Tartaric Stabilization, Malolactic Fermentation & More

Posted on Aug 26, 2024 in Chemistry

5 Tartaric Stabilization Treatments in Wine

The treatment of tartaric stabilization of wine commonly used are:

  1. Chemicals: This involves the use of additives that inhibit the formation of crystals. Among the chemicals used is mesotartaric acid, a polymer of tartaric acid obtained by heating tartaric acid at 170°C. It is added to wine and wraps the crystals of tartrate, preventing them from growing. However, this action only lasts nine months as it is hydrolyzed in the wine and transformed back into tartaric acid, losing its activity. The loss of activity is greater the higher the wine storage temperature, restricting its use to rapidly rotating wines. It is used prior to bottling, with a maximum allowance of 10 g/hl.
  2. Physical Techniques: These are based on removal techniques. The most commonly used is artificial cold treatment, which proactively causes crystallization of tartar salts to remove them from the wine. There are different types of cold stabilization techniques:
  • Traditional Cold Stabilization: The wine is cooled to -4°C and then transferred to insulated tanks for a week in the case of white wines and several weeks for red wines.
  • Contact Stabilization: Crystals of potassium tartrate are added to the pre-cooled wine. These small crystals act as seeds for the excess potassium and tartrate ions in the wine to deposit on. After four hours, the excess tartrate is removed. The wine is then centrifuged or filtered to separate the crystals. This method is fast, effective, and energy-efficient as it is performed at 0°C.
  • Continuous Stabilization: This is done in a tank called a crystallizer. The wine is cooled and circulated continuously in the crystallizer for 10-40 minutes. This method is not as effective for red wines due to the short contact time.

6 – Conditions for Malolactic Fermentation

  • pH: The optimum pH is between 4.2 and 4.5. Lower pH levels slow down the process, while higher pH levels accelerate it. Below a pH of 2.9, malolactic fermentation does not occur.
  • Temperature: The ideal temperature is 18°C. This helps avoid the attack of lactic acid bacteria on components other than malic acid, which can increase volatile acidity. Acceptable margins are between 20-28°C.
  • Alcohol Content: Above 13% v/v, the activity of malolactic bacteria is limited. While bacteria can degrade all malic acid at normal alcohol concentrations, the formation of lactic acid is greater at lower alcohol concentrations.
  • Sulfite: Sulfur is more common in yeast than bacteria. High doses of sulfite inhibit malolactic bacteria, while small doses promote their proliferation. After alcoholic fermentation, sulfite levels should be low if malolactic fermentation is desired.
  • Aeration: Both extreme anaerobic conditions and excessive aeration are negative for malolactic fermentation.
  • Nutrients: Lactic acid bacteria have greater nutrient demands than yeasts, especially for amino acids. Without sufficient nutrients, malolactic fermentation will not occur.

Based on these factors, malolactic fermentation can take anywhere from 5 days to 4 weeks. It can also stop and restart several months later.

7 – Advantages and Disadvantages of Different Types of Presses

There are four main types of presses:

  1. Vertical Press
  2. Plate Press
  3. Horizontal Plate Press
  4. Horizontal Membrane Press
  5. Continuous Screw Press

Advantages and Disadvantages:

In vertical and plate presses, the liquid exit direction is perpendicular to the applied pressure, making it difficult for the must to flow out. In membrane presses, these directions are aligned, allowing for lower working pressures. Additionally, membrane presses do not have the friction of the solid mass, which can release phenols and oxidative enzymes that give an unpleasant taste. Therefore, membrane presses generally produce higher quality must. Continuous screw presses are rarely used because they produce lower quality musts and wines with more bitter plant materials in suspension due to the high pressure required.

8 – Protein Haze

Protein haze occurs when grape proteins and yeast proteins in the wine are coagulated by heat, cold, or the presence of tannins produced during aging in oak barrels or from cork closures. In the bottle, a haze appears below the cap and can extend throughout the bottle when agitated. Red wines generally do not suffer from protein haze because the tannins from the grapes coagulate the proteins during barrel aging. White wines, however, retain proteins that need to be removed before bottling.

Treatment

To remove proteins, wine is treated with bentonite, a clay mineral with a negative charge that attracts the positively charged wine proteins and removes them through electrostatic adsorption. Bentonites are sold as powders or granules and swell in contact with water, increasing their weight tenfold and forming colloids with a large adsorbent surface area. Bentonite should be hydrated with cold or lukewarm water for up to 24 hours, then stirred to form a gel or paste, which is added to the wine gradually while stirring for at least 5-10 minutes.

Heat Test

To test for protein stability, fill a test tube with wine, add a touch of tannin, stir, and heat in a water bath at 80°C for 30 minutes. Then, cool the test tube in the refrigerator for 4 hours. After cooling, observe the clarity of the wine. If it remains clear, there is no risk of protein haze. If a veil or whitish deposit appears, it indicates the presence of proteins and potential for protein haze. In this test, the wine becomes cloudy when heated and clarifies during cooling. Tannin is used to ensure the precipitation and flocculation of proteins. The presence of proteins can also be detected with a nephelometer.

Identification of Protein Haze

To differentiate between protein haze and other types of haze, such as iron haze, perform the following tests:

  • Add a few drops of hydrochloric acid to the turbid wine. If the turbidity increases, it is protein haze.
  • Heat the turbid wine to 80°C. If the turbidity disappears, it is protein haze.

Fermentation

White wine fermentation takes place at lower temperatures than red wine fermentation (around 20°C) to avoid losing the varietal aromas. Additionally, the aromas produced by yeasts during white wine fermentation are less pleasant than those produced during red wine fermentation. Must for white wine fermentation has fewer indigenous yeasts, so the start of fermentation is often delayed. Therefore, it is common to use a yeast starter (a quantity of fermenting must that is mixed with the must to be fermented) or active dry yeast. The success of malolactic fermentation depends on whether or not it is desired for the final wine.