Regardless of whether the wine is left to mature in tanks or barrels, tests are done in the lab periodically to check the status of the wine. Tests include checking of °brix, pH, acidity, main (domestic) sugars, released or available sulfur, a total amount of sulfur, evaporating of the acids and the percentage of alcohol. These tests are usually performed during production or just before bottling. Depending on the results of these tests, winemakers can take appropriate actions to improve the quality of the wine, for example, to add more sulfur dioxide. Finally, sensory tests are performed, and again the winemakers decide whether something has to be changed, such as adding protein to soften the taste of the wine. Sugars are found in greatest amounts and therefore the levels of sugar in the wine are the most frequently measured levels. The level of sugar in the grapes is important not only because it determines the final amount of alcohol in the wine, but also because it is an indirect indicator of the maturity of the grapes.