Fred S. Nury

Production Wine Analysis

Section I-Sampling, Fermentation, and Production Analysis.- 1 / Fruit Quality and Soluble Solids.- 2 / Alcoholometry.- 3 / Extract.- 4 / Hydrogen Ion (pH) and Fixed Acids.- 5 / Volatile Acids.- 6 / Carbohydrates: Reducing Sugars.- 7 / Phenolic Compounds and Wine Color.- 8 / Oxygen, Carbon Dioxide, and Ascorbic Acid.- Section II-Microbial Stability.- 9 / Sulftir Dioxide.- 10 / Sulfur Containing Compounds.- 11 / Other Preservatives: Sorbic Acid, Benzoic Acid, and Dimethyldicarbonate.- 12 / Wine Microbiology.- Section III-Chemical Stability.- 13 / Tartaric Acid and its Salts.- 14 / Copper.- 15 / Iron and Phosphorus.- 16 / Nitrogenous Compounds.- Section IV-Remedial Actions.- 17 / Fining and Fining Agents.- 18 / Correction of Tartrate Instabilities.- 19 / Removal of Copper and Iron-The Hubach Analysis.- Appendixes.- Appendix I /Chromatographic Techniques.- Appendix II /Laboratory Reagent Preparation.- Appendix III /Laboratory Media and Stains.

Phenolic Compounds and Wine Color

Variations in wine types and styles are largely due to the concentration and composition of wine phenols. From the vineyard to production and aging, fine wines can be viewed in terms of management of phenolic compounds. Phenols are responsible for red wine color, astringency, and bitterness; they contribute to the olfactory profile; serve as important oxygen reservoirs and as substrates for browning reactions.

Iron and Phosphorus

Yeasts require trace levels of various mineral compounds including iron. At low concentrations, iron plays an important role in metabolism as an enzyme activator, stabilizer, and functional component of proteins. At higher-than-trace levels, iron has other roles: altering redox systems of the wine in favor of oxidation, affecting sensory characteristics, and participating in the formation of complexes with tannins and phosphates resulting in instabilities. This complex formation, also termed “casse,” is seen initially as a milky white cloud and later as a precipitate. Two iron-containing casses may form in wines: “white” (ferric phosphate) and “blue” (ferric tannate casse). The former represents the most commonly encountered iron-related casse.

Fining and Fining Agents

Fining is the addition of a reactive or adsorptive substance to remove or reduce the concentration of one or more undesirable constituents. Fining agents are added to juices, wines, and sparkling wine cuvees for the purposes of enhancing clarity, color, aroma, flavor, and/or stability modification. Fining agents can be grouped according to their general nature.

Sulfur Dioxide and Ascorbic Acid

In its several commercially available forms, SO2 is widely used in wine and related food indust ries as a chemical antioxidant and inhibitor of microbial activity. Although historically sulfites were generally recognized as safe, the U.S. Food and Drug Administration (FDA) has determined that the presence of unlabeled sulfites in foods and beverages poses a potential health problem to a certain class of asthmatic individuals. As a result, in 1987, the U.S. BATF implemented regulations requiring the declaration in labeling of sulfites present in alcoholic beverages at a level of greater than 10 mg/L (ppm) measured as total sulfur dioxide, by any method sanctioned by the international Association of Official Analytical Chemists (AOAC). The maximum permissible level of total sulfur dioxide for both BAIT and the OIV is 350 mg/L.

Metals, Cations, and Anions

Grapes, musts, and to a lesser extent, wine contain trace amounts of heavy metals. The term “heavy metals” distinguishes those near the bottom of the periodic table (i.e., lead, mercury, and cadmium) and metal-like elements (such as arsenic) from the common “lighter weight” metals (such as sodium, potassium, calcium, and magnesium) present in significant amounts in grapes (see Chapter 15). Heavy metals are toxic to biological systems due to their ability to deactivate enzymes. As such, their allowable concentrations in foods is regulated. In terms of decreasing concentrations normally seen in wine, these include iron, copper, zinc, manganese, aluminum, lead, and arsenic (Table 12-1).

Sulfur-Containing Compounds

Sulfur, in its various forms, is important to the yeast in protein biosynthesis as well as vitamins and coenzymes. Formation of volatile sulfur compounds plays an important role in sensory properties of wines. These compounds may be variously described as rubbery, onion, garlic, cabbage, kerosene-like, and skunky. The somewhat undefined, but objectionable character arising from interaction of sulfur-containing compounds and wine components is sometimes described as “reductive tone.” Wines exhibiting this property lack (or are deficient in) focused fruit and complexity attributes and are described as “reduced.” Sulfur is available as sulfate (SO 4 2− ), sulfite (SO 3 2− ), amino acids (methionine, cysteine, and cystine), the tripeptide glutathione, as well as the vitamins biotin and thiamine (B1), and acetyl-CoA and lipoic acid.

Tartaric Acid and Its Salts

As a principal acid in grapes and wine, tartaric acid plays an important role not only in contributing to overall wine acidity but also in the maintenance of juice and wine buffer systems. As a result of this activity, juice as well as wine is maintained (buffered) at a relatively low pH, which, in turn affects the biological stability and visible color, in addition to the overall acidic taste of the product. The tartaric acid content of grape musts varies from 0.2 to 1%, with 0.1 to 0.6% being found in most grape wines.

Tartrates and Instabilities

Tartaric acid (H2T) and its salts, potassium bitartrate (KHT) and calcium tartrate (CaT), are normal constituents of juice and wines and important to stability. The formation of crystalline deposits is a phenomenon of wine aging, although it generally does not meet with consumer acceptance. Thus, winemakers strive to reduce the potential for bottle precipitation.

Sorbic Acid, Benzoic Acid, and Dimethyldicarbonate

Sorbic acid is a short-chained unsaturated fatty acid widely used in the wine and food industry as a chemical preservative. Because sorbic acid is not readily soluble, it is usually sold as the soluble salt, potassium sorbate. Effective primarily as a fungistat, sorbic acid is added to sweet wines. Although a generally effective inhibitor of fermentative yeasts, sorbic acid has little inhibitory activity toward lactic acid bacteria, acetic acid bacteria, or oxidative film forming yeast.