Selection, grape

Anthocyanin Content in Selected Grapes and Berry Fruits... 

Total Phenolics (as Gallic Acid Equivalents, GAEs) in Selected Grapes and Berries... 

ORAC Values (pmol Trolox Equivalents/g Fresh Fruit) of Selected Grapes and Berry Fruits... 

Fermentation. Today (ca 1997) it is almost universal to inoculate the must with a selected yeast strain. Yeasts are chosen for conducting predictable, prompt, and complete fermentations under the conditions appHcable for the particular wine. It is tme, at least in most wineries, that grapes will ferment with the yeasts naturally present. At one time it was argued that part of the special regional character of wines was the result of the local yeasts. 

In addition to alcohoHc fermentation, a malolactic fermentation by certain desirable strains of lactic acid bacteria needs to be considered. Occasionally, wild strains produce off-flavors. Malolactic fermentation is desirable in many red table wines for increased stabiUty, more complex flavor, and sometimes for decreased acidity. Selected strains are often added toward the end of alcohoHc fermentation. AH the malic acid present is converted into lactic acid, with the resultant decrease of acidity and Hberation of carbon dioxide. Obviously this has more effect on the acidity the more malic acid is present, and this is the case in wine from underripe, too-tart grapes. Once malolactic fermentation has occurred, it does not recur unless another susceptible wine is blended. 

This example demonstrates the most challenging problem of flavor chemistry, ie, each flavor problem may require its own analytical approach however, a sensory analysis is always required. The remaining unknown odorants demand the most sensitive and selective techniques, and methods of concentration and isolation that preserve the sensory properties of complex and often dehcate flavors. Furthermore, some of the subtle odors in one system will be first identified in very different systems, like o-amino acetophenone in weasels and fox grapes. 

Freedman JE, Parker C 3rd, Li L, Perlman JA, Frei B, Ivanov V, Deak LR, Iafrati MD and Folts JD. 2001. Select flavonoids and whole juice from purple grapes inhibit platelet function and enhance nitric oxide release. Circulation 103 2792—2798. 

Resistance to insects has been successfully selected and introduced into important cultivars of a number of plant species including potatoes, wheat, corn, grapes, alfalfa, barley, beans sorghum, rice and sugar cane (25). This resistance is usually due to a combination of factors and only in a few cases is a single chemical factor identifiable as responsible for resistance (32). 

Alvarez et al. [73] compared the performance of LDA and ANNs to classify different classes of wines. Metal concentrations (Ca, Mg, Sr, Ba, K, Na, P, Fe, Al, Mn, Cu and Zn) were selected as chemical descriptors for discrimination because of their correlation with soil nature, geographical origin and grape variety. Both LDA and ANNs led to a perfect separation of classes, especially when multi-layer perceptron nets were trained by error back-propagation. 

Yeast Disorders. Many genera and species of yeasts are found on grapes. Undesirable yeasts must be inhibited as soon as the grapes are crushed, and the primary fermentation must be controlled by inoculating the must with pure strains of yeast. This ensures a clean fermentation in a reasonable time with efficient conversion of the grape sugars to alcohol. Selecting pure yeasts is a matter of preference for individual wineries, but the preference in the United States has been for yeasts which do not produce undesirable by-products. 

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