Showing papers in "American Journal of Enology and Viticulture in 1965"

Colorimetry of Total Phenolics with Phosphomolybdic-Phosphotungstic Acid Reagents

Abstract: Several details of the assay of total phenolic substances have been investigated and an improved procedure developed. The improvements include the use of Folin-Ciocalteu reagent rather than the Folin-Denis reagent, gallic acid as a reference standard, and a more reproducible time-temperature color development period. The values obtained are less subject to variation and interference from several nonphenols, yet are directly comparable to the "tannin" values obtained by the previously standard method.

Acids and the Acid Taste. I. The Effect of pH and Titratable Acidity

Abstract: The relative sourness of malic, citric, tartaric, and lactic acids was determined in two ways: by using the acids to change total titratable acidity by 0.1% or to change pH to 3.30. A trained laboratory panel used a ranking procedure to compare the sourness at the same titratable acidity. The order of sourness was malic> tartaric>citric>lactic. At the same pH the order was malic>lactic>citric>tartaric. All of the differences were statistically significant. Malic thus appears to be the most "sour" of the acids tasted. The tasters varied markedly in ability to rank sourness—some tasters were nearly twice as efficient as others (as measured by deviation in ranking duplicate samples). Differences of 0.05 pH unit for the four acids were easily detected by the panel. These differences in pH were accompanied by differences in titratable acidity of 0.02 to 0.05%. When titratable acidity was changed 0.02, 0.03, 0.04, and 0.05, the differences in pH were 0.03, 0.035, 0.042, and 0.093. The panel was generally able to rank the samples, except tartaric acid, in order of sourness. Malic changed the pH less than the other acids. In these studies, both pH and percent titratable acidity appeared to be important in determining sensory response to sourness.

Changes in the Concentration of Malates, Tartrates, and total free Acids in Flowers and Berries of Vitis Vinifera

Abstract: In eight grape varieties studied from April 20 to October 20, tartrate, malate, and total titratable acids increased rapidly in the flowering parts of the vine up to early bloom. The levels declined during late bloom and berry set. During prebloom and bloom periods, tartrates were present in amounts two to five times as great as the amounts of malate. After shatter, concentrations of both acids in the berries increased rapidly for about 4 weeks, a period corresponding closely to the period of rapid growth of berries. Tartrates and malates remained at a high level in about equal amounts until the berries began to change color and ripen. The ripening period (July 22 to Sept. 18) was associated with sharp decreases in malates and tartrates in all varieties. During the ripe and overripe stage of maturity, tartrates remained at about the same level, while malates and total titratable acidity continued to decrease. The varieties studied were classified into two groups according to the average ratio of tartrate to malate (T/M) at berry maturity. Low-malate varieties (T/M ratio greater than 2.5) included Thompson Seedless, White Riesling, Emerald Riesling, and Semillon. High-malate varieties (T/M ratio less than 1.5) included Sylvaner, French Colombard, Barbera, and Carignane.

Variability Among Wines to Protein Clouding

Abstract: There are four major protein fractions in wines. One of these fractions is more heat-labile than the others and has a lower isoelectric point. Protein stability in wines is apparently a function of the ratio of the amount of this fraction to the combined amount of the other fractions. pH is an important factor (but not the only one) in fixing the relative proportions of the protein fractions. More work is needed to discover the other factors involved.

Changes in Concentration of Glucose, Fructose, and Total Soluble Solids in Flowers and Berries of Vitis Vlnifera

Abstract: Concentrations of glucose, fructose, and soluble solids in the flowers and berries of eight varieties of Vitis vinifera were determined every 7 to 11 days over an entire growing season (April 20 to October 20, 1964). Concentration of glucose and fructose in the inflorescence reached a maximum at the beginning of the bloom period. Concentrations of these sugars decreased during the latter part of bloom and remained at a relatively low level until veraison. Concentrations of glucose and fructose in the berries of all varieties investigated increased from less than 1% to over 10% in 40 to 50 days following veraison. The relative concentrations of glucose and fructose were approximately the same during prebloom, bloom, ripening, and ripe stages of flower and berry development. Per cent glucose exceeded that of fructose during the green berry stage, while fructose constituted the major sugar in overripe grapes. Overripeness was associated with a sharp decrease in tne concentration of glucose in the fruit and a corresponding increase in the level of fructose.

The Formation of Succinic Acid during Alcoholic Fermentation

Abstract: During alcoholic fermentation by yeast there is an increase in total acidity and a change in the constituent organic acid composition of the fermented medium. The formation of acetic acid, widely referred to as volatile acidity, is generally recognized as a normal by-product of alcoholic fermentation. In bacteria-free fermentations, the amount of acetic acid formed does not exceed 0.03 to 0.04 g per 100 ml. By far the largest increase in acidity during fermentation is brought about by the formation of nonvolatile organic acids, and it generally varies between 0.1 to 0.4 g per 100 ml but averages about 0.2 g per 100 ml. Three strains of Saccharomyces cerevisiae widely used in California for commercial wine fermentations were studied using dormant yeast, cake or proliferating yeast slurry. The net increase of nonvolatile organic acidity was not influenced by the yeast strain. The highest rate of increase of nonvolatile organic acidity took place during the early stages of fermentation; after the fermenting medium reached 4 to 5% alcohol, the rate of increase leveled off gradually. The net increase in nonvolatile acidity was not significantly influenced by the initial pH of the fermenting medium. However, the percentage increase in nonvolatile acidity was highest with media of low initial total acidity. With most grape juice fermentations, qualitative changes in the nonvolatile acid composition of the resulting wine are obscured by the over-all decrease in total acidity brought about by the precipitation of potassium acid tartrate. Significant amounts of organic acids, not present in the grape, are formed during fermentation and perhaps influence wine quality. At least two new organic acids are formed during fermentation, which constitute the bulk of the nonvolatile organic acidity increase. Of these, about 90% is due to one acid and about 10% to the second. On the basis of paper chromatagraphy, radiochromatagraphy, infrared absorption spectroscopy, melting point, and other traditional methods of organic chemistry, it was determined that the predominant nonvolatile organic acid formed during fermentation is succinic acid (90%). Lactic acid appears to be the other acid formed in significant amounts (10%).

The Effect of Temperature on the Ripening of Sultana Grapes

Abstract: Grapes of the variety Sultana (Thompson Seedless) were exposed to a constant temperature of about 33°C for 3 months beginning about 20 days after flowering. Maturation was followed by periodic determinations of berry weight and sugar and acid content. The elevated temperature caused mainly a reduction in berry size. The start of acid decrease and the beginning of sugar accumulation were not affected by the temperature. The temperature increase led to a more rapid decrease of the acid content and for a short time to a more rapid accumulation of sugars so that the sugar-acid ratio was changed.

The Formation of Acetoin and Diacetyl during Fermentation, and the levels found in Wines

Abstract: Acetylmethylcarbinol (acetoin) formed during yeast fermentations of sugar reaches a maximum of about 25 to 100 ppm about midway through fermentation, and then largely disappears, presumably by reduction to 2,3-butanediol. The peak of acetoin content coincided with the maximum level of acetaldehyde formation, which follows a similar pattern of rise and decline. The acetoin content of sweet (dessert) wines produced by the addition of wine spirits to half fermentation was much higher (50 to 200 ppm) than corresponding dry wines produced by complete fermentation (about 5 to 20 ppm). Significantly higher levels of acetoin (up to 350 ppm) were found in sherry samples produced by the submerged flor yeast fermentation than in those of comparable baked-type sherry. However, diacetyl was not higher (less than 1 ppm) as a result of the oxidative conditions of the submerged flor process. The creatine-αnaphthol colorimetric method was used for acetoin for measurement, but it gave erroneously high values for diacetyl in the presence of acetoin, so diacetyl was determined by a colorimetric nickel dimethylglyoxime method. The possible significance of acetoinic compounds in wines is discussed.

The Sugars of Grapevines. II. Identification and Seasonal changes In The Concentration of Several Trace Sugars in Vitis Vinifera

Abstract: Sucrose, raffinose, stachyose, melibiose, and maltose were identified in the berries, leaves, and phloem of eight varieties of Vitis vinifera by paper chromatography, radioautography, and enzymatic techniques. Galactose was also found in some berry samples. Sucrose and raffinose were present in berries at all stages of fruit development except the first 2 to 3 weeks after berry set. These sugars were present in low concentrations (less than 0.05%) until after the total soluble solids reached 10 to 18°B; they were at their highest level during berry maturity, and generally decreased slightly during overmaturity. The maximum concentrations of sucrose and raffinose in the different varieties respectively varied from 0.019 to 0.18% and from 0.015 to 0.34%. The concentration of sucrose and of raffinose in mature `Thompson Seedless9 and 9Semillon9 berries was greater in the basal part than in the middle or tip sections.

Some Factors Affecting Tartrate Stability in Wine

Abstract: Four aliquots were taken of 10 red and 10 white wines. One aliquot was cation-exchanged, one anion-exchanged, one cation-plus-anion-exchanged, and one used as control. After treatment, all wines were adjusted to the same pH and then stored at refrigeration temperature with a large excess of KHT until they approached equilibrium. Anion exchange reduced the tartrate-holding capacity substantially, with cation- and cation-plus-anion exchange producing a very large reduction. Removal of pigments and other polyphenols from the red control wines by carbon, and of protein from the white control wines by bentonite, produced almost exactly the same effect as cation exchange. Changes in CP values of the wines usually resulted in unequal changes (on a molar-equivalent basis) in the potassium and tartaric acid values, instead of the equal changes that would occur if only potassium and tartaric acid were involved in the reactions. Speculations are made on the possible mechanisms involved in the observed behavior.

The main Constituents of the Surface Waxes of Varieties and Species of the Genus VITIS

Abstract: Cuticular waxes from fresh grapes and leaves of Vitis vinifera, Vitis labrusca, Vitis rupestris, several Vitis hybrids, and Parthenocissus quinquefolia were extracted with cold chloroform. The main constituent of the waxes from grapes was oleanolic acid, which is present in the surface wax of leaves in only small amounts. The chloroform extracts were separated by extraction with petroleum ether into the insoluble "hard wax", consisting mainly of oleanolic acid, and the soluble "soft wax," which was fractionated by chromatography on aluminum oxide into hydrocarbons, an "ester-aldehyde" fraction, free alcohols, and free acids. The waxes of all grape vine varieties appeared to have a similar composition except V. labrusca var Isabella, which contained a much higher amount of hydrocarbons in the cuticular wax. The compositions of the hydrocarbons, free alcohols, and free acids were determined by gas-liquid chromatography. The following chain-length distributions were found: hydrocarbons, n-C18 to n-C35, with n-C25, n-C27, n-C29 and n-C31 as main constituents; alcohols, n-C20 to n-C34, with n-C26 in grapes and n-C28 and n-C30 in leaves as main constituents; acids, n-C14 to n-C32, with n-C26 as the main constituent. Except for the high content of paraffins in V. labrusca, the differences between the analyzed varieties and species of grape vines were small.

Color Extraction by Heating whole Grapes

Abstract: Varieties were shown to react differently to heat treatment, and there was also a decided difference between dry red and port wines. Amount of initial color affected the color behavior of dry reds during aging but had no discernible effect on ports. Heated dry reds tended to be considerably more color-stable in comparison to the control wines than did heated ports. The quality of dry red wines decreased with increased heating times, whereas ports showed no effect within the range of heating times used in these experiments.

Sensory Characterization of Wines Fermented with Several Malo-Lactic Strains of Bacteria

Abstract: Malo-lactic fermentation was induced in separate lots of wine by inoculation of each lot with 1 of 6 different lactic acid bacteria isolated from California wines. The bacteria were of several genera and were biochemically diverse. Grapes of low varietal character were used so as not to obscure any flavor differences imparted to the wines by the bacteria. Malo-lactic fermentation had occurred in each inoculated wine within about 2 months. The resultant wines were subjected to sensory evaluation by an experienced wine-tasting panel. Four of the 10 members of the panel were able to distinguish consistently the malo-lactic wines one from another, but half of the panel members were also able to detect differences in the control wines.

The Occurrence of Malo-Lactic Fermentation in Southern California Wines

Abstract: A high incidence of malo-lactic fermentation was found in wines from Southern California. The results are similar to those previously found for wines from other regions of California, except that the occurrence of malo-lactic fermentation was also high in the white wines. The concentrations of acetoin (plus diacetyl) in the wines were somewhat on the high side of the range usually found. The wines with high concentrations of acetoin tended to be those that had undergone malo-lactic fermentation, but there was no significant correlation between malo-lactic fermentation and concentration of acetoin. Wines made under laboratory conditions from grapes grown in Southern California also underwent malo-lactic fermentation.

The Browning Problem in Wines

Abstract: At room temperature, a Palomino wine darkened readily in the presence of dissolved oxygen and hardly at all in its absence. On the other hand, a French Colombard wine darkened considerably in the absence of oxygen at room temperature, and this darkening was not increased appreciably by the presence of dissolved oxygen. At a higher temperature, however, oxidative browning, or oxygen-catalyzed browning did take place in the Colombard to a great extent. Nylon treatment appeared to be helpful in some cases and harmful in others. On the other hand, PVP treatment in the range of 4 to 6 pounds per 1000 gallon seemed to provide an improvement in almost all cases, although the improvement was marginal in some instances. The accelerated testing method described did not give results which correlated with the long-term storage test, indicating that although browning reactions are strongly influenced by temperature, this influence is not predictable in the light of present knowledge.

The Malo-Lactic Fermentation in New York State Wines

Abstract: Wines from Vitis labrusca grapes and their hybrids produced in New York State were examined to determine the incidence of malo-lactic fermentation. Ninety-six samples of partially ameliorated varietal wines were analyzed for organic acids by paper chromatography. Forty-five percent had undergone a malo-lactic fermentation. The incidence was much greater in red wines than in white wines. There was a marked difference in incidence among the wineries involved, and the correlation between must handling procedures and incidence of malo-lactic fermentation was noted. The time interval between the alcoholic fermentation and a malo-lactic fermentation was found to be of the order of three weeks. The conversion of malic acid to lactic acid in these wines occurred rapidly, once started, and coincided with the development of a bacterial population in excess of a million organisms per milliliter. Three types of lactic acid organisms have been isolated, a heterofermentative rod, a homofermentative rod, and a homofermentative coccus. Characteristics of musts were reported. In the new wines, the relationship between total acidity and pH, and the incidence of malo-lactic fermentation was noted.

Sugar Extraction from Grape Pomace with A 3-Stage Countercurrent System

Abstract: The main factors involved in countercurrent extraction of sugar from pomace are the liquid content of the feed, the degree of pressing, and the water added. The time the pomace is in contact with the extraction liquid is of less importance. Countercurrent extraction is a more satisfactory washing system than simple multiple-contact since satisfactory sugar levels in both product and washed pomace are easily attainable with countercurrent washing.

Treatment of White Wine with Nylon 66

Abstract: Carbon, casein, and nylon were compared as to color removal properties. Though carbon removed the greatest amount of color if had a deleterious effect on wine quality. Casein in batch treatment and nylon in column treatment were about equal in removing color from white wines. Though nylon is much more costly than casein, it can be made competitive with casein through regeneration and repeated use. Nylon is recommended for commercial trial since it does not alter wine quality and usually gives more protection against browning than does casein.

Effects of Several Nematode-Resistant Rootstocks on Vine Vigor, Crop Level, and Nutrition with the Grape Variety, Grenache

Abstract: A regulated level of pruning, in which the number of fruiting units retained is balanced with the past vegetative growth of the vine, did not entirely overcome the low-yielding tendencies of very vigorous grafted vines. Fruiting efficiency of the individual spur, based on the ratio of prunings to fruit produced, was markedly lower from vines on the very vigorous stock, Dogridge, and highest on the own-rooted Grenache vines. Over the six-year period that harvest records were obtained, the heaviest-yielding vines and those showing the best balance between growth and fruit production were on the V. Champini selection, Salt Creek. Total carbohydrate content was markedly increased and total nitrogen level decreased in the shoots by girdling during bloom. Only the yields of the vigorous vines on Dogridge were increased by this treatment. Topping the vine at bloom did not change carbohydrate levels in the shoots at the time of berry shatter, but gave some reduction in vine vigor. A growth retardant, maleic hydrazide, used at 500 ppm as a foliar spray during bloom, was not effective in changing nutrient levels in the shoots. However, evident leaf symptoms and reduction in shoot elongation was noted late in the growing season.

Some Responses of Grapevines to Treatment for Frost in Napa Valley

Abstract: Removal of frost-injured shoots by stripping out or cutting them off failed to produce significant increases in yield of fruit over vines receiving no treatment. The lack of significant response was shown for one spur-pruned variety and two cane-pruned varieties of wine grapes. The per cent total carbohydrate, calculated on a dry-weight basis, of the shoots, spur bark, and spur wood in late April failed to show significantly lower levels when correlated with the length of shoot development. Cluster weights but not berry weights were heavier for clusters produced on shoots growing from primary buds than for clusters and berries on shoots growing from secondary or tertiary buds. Maturity began at an earlier date and was higher at time of harvest in clusters from primary buds not injured by frost.

Studies with Controlled Fermentations IX. Bentonite Treatment of Grape Juice Prior to Wine Fermentation

Abstract: Studies of the pre-treatment of white grape juice with bentonite were made to determine effects on fermentation rates, stability, and quality. The effect of the treatment on natural sweet table wines and on dry table wines is discussed, and details are given. Amounts of bentonite needed to get desired effects were found to be large (8 g/l) for the natural table wines. Smaller amounts (0.6 g/l) help protein stabilize dry wines. There was no quality deterioration or improvement by the use of the bentonite on these samples.

Two-Wire Horizontal Trellis for Thompson Seedless Raisin Production

Abstract: Field trials were conducted in 4 Fresno County Thompson Seedless raisin vineyards to compare a 22-inch horizontal trellis about 48 inches aboveground with a standard one-wire trellis at the same height. Raisin yields, average berry weights, soluble solids, and total acid determinations were taken for 3 years. Raisin yields were usually significantly increased with the horizontal or flat-top trellis. In one test, increased yield was partially due to higher soluble solids. The increase in yield was probably due to a greater number of berries which would result from more clusters and/or larger clusters. The increase in the number of berries might be due to more mature renewal fruit canes. Shoots used for renewal canes are supported by the wires in a horizontal trellis and thus are better exposed to light than with a one-wire trellis, where these shoots hang downward and are often shaded. Expanse of the leaf area is greater with a horizontal or wide-top trellis than with a single wire trellis. The horizontal trellis also spreads and supports the shoots, which should provide for better leaf exposure.

Characteristics of Sequential Measurements on Grape Juice and Must

Abstract: Three series of determinations—refractometer, pH, and titratable acidity—were made on must for 154 sets of 2 or 3 boxes of grapes, and two series of readings—refractometer and pH—were made on juice from berries for 310 boxes of grapes harvested in a systematic way. If the series were regarded as being random the distributions were nonnormal, indicating vineyard heterogeneity. Plots against box number indicated decided oscillations in the data. The vineyard variations that are detected and described here are more subtle than can be handled by usual field trial designs.