Basic analysis of wine and must

In our certified oenological laboratory, all analyses are performed on must and wine, such as: acidity, pH, sugars, alcohol content, total and molecular sulfur dioxide, protein instability, and others as needed to assess the progress and necessary correction.

Acidity is the element that gives us the sensation of freshness, vibrancy, and intensity when we taste a wine, making its taste sharper. The anti-microbial properties of wines are due to acidity and its combination with alcohol. The main acids derived from grape berries are Tartaric acid, Malic acid, and secondarily Citric acid.

Tartaric acid is not found in other fruits of nature except grapes. Its concentration in the must of ripe grapes in northern wine regions reaches up to 6 grams per liter, while in southern and warmer regions it reaches 2-3 grams per liter. It is a strong acid, also responsible for shaping the pH in wine. A decrease in tartaric acid content can be observed at low temperatures due to the insolubilization of tartrate salts.

Malic acid is found in all living organisms. It comes from the metabolism of sugars and is found in abundance in apples. It is also found in grape berries.

Citric acid is also widespread in nature and is contained in large quantities in citrus fruits, especially lemons. Its concentration in must ranges between 0.5 and 1g/L. It can be converted to acetic acid by lactic bacteria, which is why its addition to wine should be avoided.

The pH in winemaking usually has the following values:

Must: 3.2 – 3.5
White and Rosé wines (dry): 3.2 – 3.5
Red wines (dry): 3.3 – 3.8
Semi-sweet and sweet wines: 3.8 – 4.5

The lower the pH value, the more "acidic" our wine is. This requires a little attention because we often hear about wines with "High Acidity". This expression refers to the sensation of acidity we have during the organoleptic tasting of the wine, not to the value of the measured Total Acidity or at least thats how it should be, and certainly not to the pH.

How "acidic" a wine is or not is checked by measuring the pH and not by measuring the Total Acidity. Usually (not always) a wine with High Acidity (in taste) has high Total Acidity (measured) and low pH. However, sometimes (quite often for me) an acidic wine has low total acidity and low pH.

This is because when measuring Total Acidity, we measure the acids in the wine without taking into account their strength. In contrast, with pH, we measure the acidity of the wine taking into account the strength of each acid involved in the formation of its acidic taste. Technologically, both measurements must be taken, and we must check if they are within the limits acceptable to us.

The pH meter therefore measures the Active Acidity of the wine and gives us a direct indication of whether it is acidic or not.

Sugars are the most important component of must, as its content determines the alcoholic strength of the wine that will result after alcoholic fermentation.
The total amount of sugars in must ranges from 150 to 300 g/L, and consists mainly of an almost equimolar mixture of D-glucose and D-fructose. In minimal amounts, there is also D-galactose (0.1 g/L), sucrose (0.3 g/L), and pentoses (arabinose, xylose, ribose, etc.).
After alcoholic fermentation, dry wines should not contain more than 4 g of sugars/L of wine.
The determination of sugars involves two stages: clarification and the main determination.

The alcoholic strength or alcoholic title by volume or Gay-Lussac degree (G.L.) of a hydroalcoholic solution is a unit of measurement of the alcohol content by volume in such solutions, such as beverages. It is defined as the amount of absolute (anhydrous) ethanol (in liters) present in 100 liters of the solution at 20°C. It is symbolized as % vol.

The amount of ethanol (in ml) is the mass of ethanol divided by its density (0.78924 g/ml) at 20°C. The International Organization of Legal Metrology[1] has analytical tables for hydroalcoholic mixtures of various densities and temperatures. The alcoholic strength is also expressed in degrees Gay-Lussac (after the French chemist Joseph Louis Gay-Lussac), although there is a small difference in the measured values, as Gay-Lussac used 15°C as the reference temperature.

The alcoholic strength is expressed as a percentage by volume concentration and is symbolized similarly to thermometer degrees (e.g., 90° vol.), and is determined by a special laboratory instrument, a hydrometer specifically called an alcoholometer.

The alcoholic strength is mandatorily indicated visibly on all alcoholic beverages sold commercially.
The mixing of two aqueous solutions of alcohol of different concentrations usually causes a change in the final total volume. The mixing of distilled water with an alcohol solution with a concentration of less than 24% vol. causes a small increase in the total volume, while the mixing of two alcoholic solutions with a concentration greater than 24% vol. causes a decrease in the final volume. The phenomenon of volume change upon mixing dissimilar solutions is explained by the concept of partial molar volume.

Sulfites are chemical compounds of sulfur, such as sulfur dioxide (SO2).
Sulfur dioxide (SO2) is a natural chemical compound that nature uses to prevent the growth of microbes.
Natural sulfites are found in the skins of grapes, onions, garlic, and many other plants. Sulfur dioxide (SO2) is a byproduct of natural fermentation.
Sulfur dioxide or sulfite (SO2) is a widely used and controversial additive in winemaking. The main functions of sulfite are to inhibit or destroy unwanted yeasts and bacteria and to protect the wine from oxidation. Oxidation is the reaction of wine with oxygen. Oxidation causes a change
 in the color and aromas of the wine and can eventually turn it into vinegar faster. The concentration levels of sulfite in a wine are measured in specialized oenological laboratories.
The presence of sulfite in small and permissible quantities (20 - 25 mg/lt) is a known classic phenomenon for every wine, and all winemakers confirm this.