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w w w. v w m m e d i a . c o m J a n - F e b 2 016 | V I N E YA R D & W I N E RY M A N A G E M E N T 7 9 and maintaining pH measuring equipment and reagents. UNDERSTANDING pH MEASUREMENT pH measurement has an impor- tant role in winemaking. The pro- cess starts when the winegrower or winemaker must decide when to harvest the grapes. The decision is based on data obtained by mea- suring Brix and pH in a sample of crushed grapes. Measuring the pH directly is usually done with a pH meter and pH electrode, while total acidity is measured by performing a titration to determine the level of acidity of the grape sample. As grapes mature, they become sweet- er and lower in acidity, so their pH increases, as does their Brix value. According to Linda Bisson, a pro- fessor and geneticist at UC Davis, optimal sugar/acidity balance is achieved if the Brix value times the square of the pH is in the range of 220 to 260. So, using this formula, a 22 °Brix juice at 3.2 pH would have a value of 225.3. The vintner also has the oppor- tunity to influence the character of the final wine by adjusting the must before fermentation. The pH of must can affect bacterial and yeast growth during fermentation. While yeasts are very low-pH- tolerant, Saccharomyces is able to grow across a wide pH range, from pH 3.0 to 8.0; and many bac- terial species in wine are inhibited at pH values below 3.5. Low-pH juices, therefore, favor the growth of yeasts rather than bacteria. The pH value also influences the amount of sulfite that is present in a free, or inhibitory, form after addi- tion of antimicrobial agents such as sulfite salts. Adjustments to pH can include addition of tartaric acid, which is naturally present in grapes, to increase acidity. Since tartaric acid is not con- sumed by yeast, or by any other microorganism in the winemaking process, it is a very effective acidi- fying agent. If the must is too acid- ic, it can be de-acidified by adding calcium or potassium carbonate. But this is a laborious process and one that takes a certain amount of skill to accomplish. An easier way to de-acidify wine is to use a secondary malolactic fer- mentation after the main fermenta- tion is complete. If the fruit source is high in malic acid, one can intro- duce commercial strains of lactic acid bacteria that will consume the malic acid and turn it one-for-one into lactic acid, a much milder acid, increasing the pH of the wine by one- or two-tenths of a pH unit. The winemaker should continue to monitor the pH and sulfur diox- ide levels of the wine post fermen- tation, throughout the rest of the winemaking process, to ensure wine quality. Wine pH even should be checked after bottling and fur- ther aging to ensure that it is within the desired levels. PH MEASURING TECHNIQUES People were producing wine long before scientific tests were available, but modern-day wine- makers have an assortment of tools In the book "Technol- ogy of Winemaking," by Amerine A. Maynard, the following pH ranges are recommended for wine musts: + White Wines < 3.3 + Red Wines < 3.4 + Sweet Wines < 3.4 + Dessert Wines < 3.6 pH RANGES Letina tanks, sanitary valves and fittings. St. Patrick's of Texas • StPats.com 50,000 square feet of Stainless Steel