Chenin Blanc Research Articles

Leaf Area/Crop Weight Ratios of Grapevines: Influence on Fruit Composition and Wine Quality

The fruiting capacity of grapevines in a given climatic region is largely determined by their total leaf area and by the percentage of the total leaf surface area that is exposed to full sunlight, provided other factors are not limiting growth and the initiation of fruit primordia. A wide range of leaf area/crop weight ratios were investigated by pruning to different levels of buds per vine, by different degrees of defoliation, and/or by cluster thinning of grape cultivars Thompson Seedless, Tokay, Chenin blanc, and Cabernet Sauvignon located at Davis or Oakville, California. For single-canopy (SC) type trellis-training systems, the leaf area/crop weight ratio required for maximum level of total soluble solids, berry weight, and berry coloration at harvest ranged from 0.8 to 1.2 m²/kg, whereas for horizontally divided-canopy (DC) type trellis-training systems (GDC, lyre, wye), this ratio was reduced to 0.5 to 0.8 m² leaf area per kg fruit. Optimal crop yield/pruning weight, pruning weight (kg) per m canopy length, leaf area (m²) per m canopy length, and leaf area density (m²/m³) for SC systems ranged from 4.0 to 10, 0.5 to 1.0 kg/m, 2 to 5 m²/m, and 3 to 7 m²m⁻³, respectively. Similarly, for DC systems these ratios ranged from 5.0 to 10, 0.4 to 0.8 kg/m, 2 to 4 m²/m, and 3 to 6 m²m⁻³, respectively. Grapevines with ratios that fell within the ranges given above for each of these five parameters were considered well balanced and capable of producing high-quality fruit and wines.

Abundance and Feeding ofHomalodisca coagulata(Hemiptera: Auchenorrhyncha: Cicadellidae) onVitisGenotypes in North Florida

Abstract The abundance of Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) was examined in north Florida from 2001 to 2003 on the following Vitis genotypes: V. rotundifolia Michx. (cultivars ‘Carlos’, ‘Early Fry’, ‘Regale’, and ‘Noble’), V. rupestris Scheele. (cultivars ‘St. George’ and ‘Constancia’), V. simpsoni Munson (cultivar ‘Pixiola’), V. champini Planch. (cultivars ‘Dogridge’ and ‘Ramsey’), and V. vinifera L. (cultivars ‘Chardonnay’, ‘Chenin blanc’, and ‘Exotic’). The mean number of adult H. coagulata was less than two per vine per day during 2001 and was lowest on V. rotundifolia cultivars. During June/July 2002, the number of leafhoppers varied between 2 per vine per day on V. rotundifolia cultivars and 10–20 per vine per day on the other Vitis genotypes. The distribution of H. coagulata was examined from June to September 2002 and during August 2003 in relation to the primary organic nutrients (19 amino acids, 7 organic acids, and 3 sugars) in xylem fluid. The concentrations of most amino a...

Clarification of Wines Using Polysaccharides Extracted from Seaweeds

The stabilization of wines often requires the use of negatively charged clarifying agents to remove proteins. The polysaccharides agar, carrageenan, and alginic acid extracted from seaweeds are negatively charged at low pH and can electrostatically bind and precipitate positively charged proteins from aqueous solutions. The objective of this study was to evaluate the capacity of agar, carrageenan, and alginic acid extracted from seaweeds to flocculate and precipitate proteins in wine. The flocculation and precipitation capacity of proteins by purified carrageenan, dried carrageenophytes, purified alginic acid, and dried alginophytes was 2-fold greater than that of agar and agarophytes. The greater flocculation capacity of carrageenan and alginic acid is likely the result of their greater number of free negative charges relative to those of agar. Although proteins were flocculated by seaweed polysaccharides, tannins were not adsorbed by agar, carrageenan, or alginic acid. The adsorption capacity of alginic acid was maximum at protein levels lower than 50 mg L⁻¹; however, carrageenan adsorbed and precipitated most proteins at concentrations surpassing 400 mg L⁻¹. The protein fraction adsorbed by agar, carrageenan, alginic acid, and seaweeds in Chenin blanc wine was also similar to the protein fraction adsorbed by bentonite. Collectively, results indicate that carrageenan and alginic acid might have a greater wine stabilization capacity than agar without modifying the tannin composition of wines.

Antioxidant activity of South African red and white cultivar wines and selected phenolic compounds: In vitro inhibition of microsomal lipid peroxidation

In vitro inhibition of microsomal lipid peroxidation (MLP) by the major South African red (Cabernet Sauvignon, Ruby Cabernet, Pinotage, Shiraz, Merlot) and white (Sauvignon blanc, Chenin blanc, Chardonnay, Colombard) commercial cultivar wines is presented for the first time. Of the red wines, Merlot was the most effective MLP inhibitor, with Ruby Cabernet and Pinotage being the least effective. Of the white wines, Chenin blanc and Chardonnay were the least and most effective MLP inhibitor, respectively. The mean antioxidant potencies (AP) of the red and white wine total phenols were 14.25 and 4.19, respectively. Ascorbic acid, present in some white wines, counteracted their ability to inhibit MLP. Inhibition of MLP significantly ( P<0.001) correlated with the total phenol content of red ( r=0.90) and white ( r=0.73) wines, as well as the flavanol content ( r=0.88) of red wines and the flavanol ( r=0.79) and tartaric acid ester ( r=0.73) contents of white wines. The MLP inhibitory activities of selected flavonoids were in the order: Quercetin > procyanidin B3 > malvidin > cyanidin ≈ (−)-epicatechin > (+)-catechin ≈ delphinidin.

The Use of Candida pulcherrima in Combination with Saccharomyces cerevisiae for the Production of Chenin blanc Wine

Wine fermentations are conducted by naturally occurring or selected industrial wine yeast strains of Saccharomyces cerevisiae. However, non-Saccharomyces yeasts also occur naturally in fermenting grape musts, especially in the initial stages of the fermentation. It has been speculated that these yeasts can contribute to the overall characteristics of the wine. Generally, it is accepted that Kloeckera apiculata is the predominant non-Saccharomyces yeast species in grape must. However, it was shown previously that Candida pulcherrima was the predominant non-Saccharomyces yeast species in a grape must after sedimentation and prior to inoculation with commercial wine yeast. Subsequently, this yeast was investigated in laboratory and small-scale wine fermentations of Chenin blanc wine. As it could not ferment grape juice to dryness on its own, it was used in combination with a S. cerevisiae wine yeast strain. The effect of SO2, di-ammonium phosphate (DAP), pH and temperature on the growth of C. pulcherrima was also investigated. In combined fermentations, no change in overall fermentation rate or standard wine chemical analyses could be observed in comparison to a control S. cerevisiae fermentation. However, wine production in three consecutive years showed that the wine produced by the combined fermentation was of higher quality than that produced by the S. cerevisiae only.

Antioxidant activity of South African red and white cultivar wines: free radical scavenging.

The free radical scavenging activity of South African red (n = 46) and white (n = 40) cultivar wines was determined using 2,2'-azinobis(3-ethylbenzothialozinesulfonic acid) radical cations (ABTS(.+)) and 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH.). The total antioxidant activities (TAA) of red and white wines using ABTS(.+) were 14.916 and 0.939 mM Trolox, respectively, at corresponding total phenol (TP) contents of 2339.0 and 273.8 mg of gallic acid equiv/L. Ruby Cabernet wines had the lowest TAA(ABTS) (13.177 mM Trolox) of the red wines, whereas the TAA(ABTS) values of Chardonnay and Chenin blanc wines were the highest (1.060 mM Trolox) and lowest (0.800 mM Trolox) of the white wines. The TAA(DPPH) values were of the same magnitude as the TAA(ABTS) values, and similar trends were observed. TAA correlated (P < 0.001) with total phenol content of red (r = 0.935) and white (r = 0.907) wines, as well as flavanol content of red wines (r = 0.866) and tartaric acid ester content of white wines (r = 0.767). Canonical discriminant analysis using phenolic composition and antioxidant activity was applied to differentiate between red and white cultivar wines.

Evaluation of Yeast Strains during Fermentation of Riesling and Chenin blanc Musts

Ten strains of <i>Saccharomyces cerevisiae</i> (V1116, D254, UCD 522, Bourgoblanc, EC1118, UCD 595, S6U, Wadenswil 27, 71B, T73) were evaluated in terms of their impact on the chemical composition of fermenting Riesling and Chenin blanc musts and on the sensory characteristics of their resultant wines. All yeasts completely utilized glucose present. Fructose concentrations in finished wines ranged from 1.5 to 7.0 g/L and were highest in UCD 595. Glycerol concentration was highest in Bourgoblanc and lowest in T73. Ethanol production was similar among the various strains, although UCD 522 produced higher ethanol than D254. Some differences existed between the yeasts in terms of production and/or use of six organic acids (citric, tartaric, malic, succinic, lactic, and acetic). Lowest tartaric and malic acids were found in 71B fermentations, while highest acetic acid concentrations were measured in both 71B and Wadenswil 27. Wadenswil 27 fermentations also contained highest tartaric, succinic (along with Bourgoblanc), and lactic acids. Highest citric acid was found in S6U fermentations, while both S6U and V1116 contained lowest acetic acid concentrations. T73 contained highest malate and lowest citrate. Sensory evaluation of Riesling wines showed that most yeasts produced more intense aromas and flavors than those fermented with EC1118. Wadenswil 27 produced Chenin blanc wines with more aroma and flavor intensity than EC1118.

High Alcohol Wine Production from Grape Juice Concentrates

Improved fermentation methods for grape juice concentrates could allow fermentation of high alcohol wines from concentrate, which may eliminate brandy fortification, provide an easier process to produce dessert wines, and prevent stuck fermentations. Two studies to determine fermentation conditions for the production of high alcohol wine from grape juice concentrates were conducted. The yeast strain in both studies was <i>Saccharomyces cerevisiae</i> L2226. Wines were fermented in flasks on an orbital shaker to increase fermentation rate and keep the yeast cells suspended. Study 1 investigated the production of high alcohol wine from concentrates of four varietals (Chardonnay, Chenin blanc, Rubired, and Sauvignon blanc) reconstituted from 68 to 35 °Brix, inoculated with different yeast levels (4 x 10⁶ or 17 x 10⁶ cells/mL), and with nutrients (Fermaid or diammonium phosphate) added alone or in combination. Treatments containing the highest inoculation level and nutrients resulted in the highest alcohol content. The highest alcohol level (18.15%) was achieved using Sauvignon blanc concentrate inoculated with 17 x 10⁶ cells/mL yeast and 2 g/ L each of Fermaid and diammonium phosphate. Study 2 examined aeration (0, 0 to 48, and 30 to 48 hr), nutrient addition method (at the start or in increments), and fermentation of 20 °Brix juice with supplementation of concentrate during fermentation versus starting the fermentation at 35 °Brix. High alcohol wines (over 20%) were made by fermentation of grape juice concentrate. Moderate aeration of fermenting juice resulted in higher alcohol levels than treatments that were not aerated. The addition of nutrients in increments resulted in lower alcohol concentrations than treatments with nutrients added at the start of fermentation. The addition of concentrate during fermentation decreased production of alcohol compared to fermentation at 35 °Brix. The highest mean alcohol level (20.96%) was produced from 35 °Brix juice aerated 0 to 48 hr with nutrients added at the start of fermentation.

Effect of Increased Yeast Alcohol Acetyltransferase Activity on Flavor Profiles of Wine and Distillates

The distinctive flavor of wine, brandy, and other grape-derived alcoholic beverages is affected by many compounds, including esters produced during alcoholic fermentation. The characteristic fruity odors of the fermentation bouquet are primarily due to a mixture of hexyl acetate, ethyl caproate (apple-like aroma), iso-amyl acetate (banana-like aroma), ethyl caprylate (apple-like aroma), and 2-phenylethyl acetate (fruity, flowery flavor with a honey note). The objective of this study was to investigate the feasibility of improving the aroma of wine and distillates by overexpressing one of the endogenous yeast genes that controls acetate ester production during fermentation. The synthesis of acetate esters by the wine yeast Saccharomyces cerevisiae during fermentation is ascribed to at least three acetyltransferase activities, namely, alcohol acetyltransferase (AAT), ethanol acetyltransferase, and iso-amyl AAT. To investigate the effect of increased AAT activity on the sensory quality of Chenin blanc wines and distillates from Colombar base wines, we have overexpressed the alcohol acetyltransferase gene (ATF1) of S. cerevisiae. The ATF1 gene, located on chromosome XV, was cloned from a widely used commercial wine yeast strain of S. cerevisiae, VIN13, and placed under the control of the constitutive yeast phosphoglycerate kinase gene (PGK1) promoter and terminator. Chromoblot analysis confirmed the integration of the modified copy of ATF1 into the genome of three commercial wine yeast strains (VIN7, VIN13, and WE228). Northern blot analysis indicated constitutive expression of ATF1 at high levels in these yeast transformants. The levels of ethyl acetate, iso-amyl acetate, and 2-phenylethyl acetate increased 3- to 10-fold, 3.8- to 12-fold, and 2- to 10-fold, respectively, depending on the fermentation temperature, cultivar, and yeast strain used. The concentrations of ethyl caprate, ethyl caprylate, and hexyl acetate only showed minor changes, whereas the acetic acid concentration decreased by more than half. These changes in the wine and distillate composition had a pronounced effect on the solvent or chemical aroma (associated with ethyl acetate and iso-amyl acetate) and the herbaceous and heads-associated aromas of the final distillate and the solvent or chemical and fruity or flowery characters of the Chenin blanc wines. This study establishes the concept that the overexpression of acetyltransferase genes such as ATF1 could profoundly affect the flavor profiles of wines and distillates deficient in aroma, thereby paving the way for the production of products maintaining a fruitier character for longer periods after bottling.

Formation of Hydrogen Sulfide and Glutathione During Fermentation of White Grape Musts

Volatile sulfur compounds (VSCs) and nonvolatile thiol-containing compounds (NVTCs), which are potential precursors of VSCs, were monitored by gas chromatography during fermentation of eight white grape musts: one Thompson Seedless, one Palomino, one Chenin blanc, two Sauvignon blancs, and three Chardonnays. The assimilable amino acid (EAA) concentration of the musts ranged from 480 mg/L to 2022 mg/L (mean = 1131 mg/L). Using a GC-flame photometric detector, three sulfur containing peaks were tentatively identified based on their retention times: hydrogen sulfide (H₂S), ethylmercaptan, dimethylsulfide, and one unknown peak (RT, 9.7 min) was detected. The predominant VSC, H₂S, was continuously produced throughout fermentation and was highest during rapid growth phase of yeast. All juices produced H₂S most rapidly during rapid yeast growth, but musts with low EAA generally produced higher levels of H₂S throughout the fermentation. Total H₂S, which ranged from 112 to 516 mg/L, was inversely correlated with concentration of assimilable amino acids (<i>p</i> &lt; 0.01) and with total nitrogen content (<i>p</i> &lt; 0.10). H₂S at the end of fermentation was negatively correlated with EAA (<i>p</i> &lt; 0.01) and positively with days to dryness (<i>p</i> &lt; 0.05). For all musts, concentration of NVTCs, primarily glutathione (GSH), steadily increased towards the end of fermentation. Final wine concentration of GSH (0.1 to 5.1 mg/L) was correlated with both total N (<i>p</i> &lt; 0.01) and EAA (<i>p</i> &lt; 0.05).

Genetic Similarities among Wine Grape Cultivars Revealed by Restriction Fragment-length Polymorphism (RFLP) Analysis

RFLP data were used to assess genetic similarity among 33 Vitis vinifera L. cultivars and one interspecific cultivar. A similarity matrix was constructed on the basis of the presence or absence of 49 bands generated by eight RFLP probes and cluster analysis was performed. The mean similarity index for all pairwise comparisons was 0.696 and ranged from 0.444 between `St. Emilion' and the interspecific hybrid `Salvador' to 0.952 between `Chenin blanc' and `Semillon'. Mean similarity among all V. vinifera cultivars was 0.705. Several groupings of similar cultivars are consistent with historical reports and presumed geographic origins: `Chardonnay' and `Melon', `Colombard' and `Folle blanche', `Gewürztraminer' and `Trousseau', `Cabernet franc' and `Cabernet Sauvignon', `Mission' and `Palomino'. The similarity between `Mission' and `Palomino' is the first genetic evidence to support the putative Spanish origin of `Mission'. Some groupings are unexpected (`Sauvignon blanc' and `Gewürztraminer', `Chenin blanc' and `Semillon') because the cultivars are not thought to have originated in the same regions. While some relationships suggested by this study may be artifacts of RFLP analysis or of the statistical method, they raise questions for further genetic inquiry into the origins of grape cultivars.

Free Amino Acid Composition of Grape Juice From 12Vitis viniferaCultivars in Washington

Free amino acid concentrations in juice of 12 <i>Vitis vinifera</i> cultivars grown in the Columbia and Yakima Valley appellations of Washington state were monitored from 1986 to 1990 for a total of 728 samples. When averaged across all years, arginine (expressed as mg/L) was the predominant amino acid in Gewürztraminer, Muscat Canelli, Semillon, and Pinot noir juices. Proline was predominant in juices of Chenin blanc, Chardonnay, Cabernet Sauvignon, Grenache, Lemberger, Merlot, Sauvignon blanc, and White Riesling. However, arginine concentration varied widely between years. Arginine, proline, proline:arginine ratio, total free α-amino acid and total free α-amino N concentrations were not correlated with soluble solids concentration at harvest. Washington juices tended to be lower in amino acid concentration than those reported for the same cultivars in California. More than 60% of the juice samples of each cultivar contained less than 400 mg total free α-amino N/L. This percentage was over 80% for all but Gewürztraminer and Muscat Canelli. All of the Cabernet Sauvignon, Lemberger, and Merlot juice samples contained less than 400 mg total free α-amino N/ L. Additionally, 93% of the Cabernet Sauvignon and 88% of the Merlot juices contained less than 200 mg total free α-amino N/L. Of the white-fruited cultivars, White Riesling (96%), Chenin blanc (94%), and Sauvignon blanc (92%) juices had the highest percentage of samples under 400 mg total free α-amino N/L. Seventy-seven percent of the White Riesling juices contained less than 200 mg total free α-amino N/L. Across all samples, 39% contained less than 150 mg total free α-amino N/L of juice, 58% contained less than 200 mg total free α-amino N/L of juice, and 90% contained less than 400 mg free α-amino N/L of juice.

The Influence of Phosphorus Availability, Scion, and Rootstock on Grapevine Shoot Growth, Leaf Area, and Petiole Phosphorus Concentration

Cabernet Sauvignon (CS) and Chenin blanc (Cb) scions on Freedom, AxR#1, St. George, and 110R rootstocks were grown under conditions of sufficient (+P) and deficient (-P) soil phosphorous availability. Shoot length, shoot dry weight, leaf area, and petiole P concentration were lower for -P compared to +P vines. Cb vines had larger leaves and more leaf area than CS vines and the leaf area of Cb vines was less inhibited by exposure to -P than was CS vines. Vines on Freedom had longer shoots, greater shoot biomass, and greater leaf area than vines on other rootstocks regardless of P availability. Under +P vines on St. George produced less shoot dry weight than vines on Freedom, but more than vines on 110R. However, the shoot dry weight and leaf area of vines on St. George was greatly inhibited by -P and vines on St. George appeared to not use P efficiently for growth under these conditions. Vines on 110R produced the least amount of shoot growth and leaf area among the rootstocks under +P, but were also the least inhibited by -P conditions. The shoot dry weight and leaf area of vines on AxR#1 was intermediate between vines on Freedom and vines on St. George and 110R, and were inhibited by -P slightly less than St. George. Freedom and 110R are more suitable for low P soils than St. George and AxR#1.

The Influence of Phosphorus Availability and Rootstock on Root System Characteristics, Phosphorus Uptake, Phosphorus Partitioning, and Growth Efficiency

Chenin blanc grapevines on either Freedom or St. George rootstock were grown under sufficient (+P) and deficient (-P) soil phosphorus availability. Root system morphology was similar for both rootstocks regardless of P availability. Vines on Freedom accumulated more P than did vines on St. George, especially under -P. There was a marked decrease in the amount of P translocated to the shoot and accumulated in the petioles of vines on St. George with decreasing P availability. Also, vines on Freedom produced more shoot growth per unit P than did vines on St. George, particularly under -P, although P use efficiency for overall vine growth was not influenced greatly by rootstock. Differences in P uptake, translocation, and growth efficiency may account for differences in shoot growth inhibition between vines on St. George and Freedom observed in our earlier study. Vines on the different rootstocks partitioned different amounts of P into petioles under +P, but not under P-deficient conditions.

Effect of Nitrogen Fertilizer Timing and Rate on Inorganic Nitrogen Status, Fruit Composition, and Yield of Grapevines

A four-year (1987-90) trial was conducted to study the effects of timing and rate of N fertilizer application on furrow-irrigated Barbera, Grenache, French Colombard, and Chenin blanc grapevines. The objectives were to further determine optimum N fertilizer practices for important wine cultivars in the San Joaquin Valley and to compare inorganic N constituents, NO₃^--N and NH₄⁺-N, for N status determination. The six treatments included four N fertilizer application timings at budbreak (BB), fruit set (FS), veraison (V), and post-harvest (PH) with a 56 kg N/ha rate, as well as BB with a 2X rate of 112 kg N/ha and control (C0). Vine N status was determined by NO₃^--N and NH₄⁺-N levels and their sum, total inorganic N (TN), in bloom and veraison petioles. Yield and fruit composition parameters were measured for vine response. Cultivar responses varied widely, with Grenache and Barbera being the high and low extreme cultivars, respectively, in petiole TN status and responsiveness to N treatment; French Colombard and Chenin blanc were intermediate. Generally, TN status increased with increasing N rate (C0 • BB56 • BB112). Nitrogen fertilizer timing demonstrated that the more recent N applications often resulted in a higher petiole TN status at the next petiole sampling; <i>i.e.</i>, PH56 and BB56 treatment petioles had higher TN status at bloom while FS56 was higher at veraison. Post-harvest timing was found to be particularly effective in supplying petiole TN in the spring; <i>i.e.</i>, PH56 sometimes resulted in bloom petiole TN levels comparable to BB112 in all four cultivars and higher than BB56 in Grenache, French Colombard, and Chenin blanc. Petiole NO₃^--N levels were more sensitive than NH₄⁺-N levels to fertilizer treatment. The greater contribution of NO₃^--N to TN and their high correlation coefficients as compared to NH₄⁺-N and TN would place in question the utilization of NH₄⁺-N as an additional measurement of N status. Grape soluble solids was the most responsive fruit parameter to N treatment. Generally, N fertilizer decreased soluble solids over C0, irrespective of timing, and with the highest rate (112 kg N/ha) resulting in the largest decrease. Grape yields were only affected in Grenache, with all of the N treatments increasing yields over C0 except V56. This result, plus other negative effects of the V56 treatment, suggest that veraison was the least desirable timing of those compared. Otherwise, timing effects on fruit parameters were minor.

Reductions in Yield and Vegetative Growth of Grapevines Due to Eutypa Dieback

Eutypa dieback of grapevines is a serious canker disease that slowly kills vines, but there is little information on yield reduction of declining vines. The severity of Eutypa dieback on individual grapevines was assessed in 1991 and 1992 as the proportion of the vines'spurs killed or symptomatic. In each year, Eutypa dieback caused a significant reduction in yield of infected vines compared with healthy vines. The linear relationship between disease severity (d) and yield (y), expressed as a percentage of the yield of healthy vines, was y=101.0-90.26d (r 2 =0.70) in 1991, and y=100.1-98.81d (r 2 =0.79) in 1992. The slope of this relationship was not significantly different between years or among five vineyards of two cultivars (Chenin blanc and French Colombard) [...]

Water use of Vitis vinifera grapes in Washington

A long-term research project was initiated in 1983 on a 1.2 ha trickle-irrigated Vitis vinifera vineyard to address water management of White Riesling (WR), Chenin blanc (CB), and Cabernet Sauvignon (CS) grapes in central Washington. Six large drainage lysimeters, two per cultivar, were installed to monitor crop water use. Each lysimeter contained two vines. Vines were balance pruned and shoot-thinned to achieve an equivalent crop level of about 15 Mg/ha of grapes. Analyses showed that published crop coefficients (ET o) for mature grapes greatly overestimate water use early and late in the season for Washington conditions although peak crop coefficients of about 0.8-0.9 were similar. Annual crop water use for all three cultivars ranged from 130 mm for one-year-old vines in 1985 to as much as 540 mm for mature vines in 1990. The average crop water use for small, young vines (1985–1986) was about 146 mm/yr, and from 1987–1990 for mature plants it was about 417 mm/yr for all three cultivars.

EFFECT of PASTEURIZATION ON MICROBIOLOGICAL and SENSORY QUALITY of WHITE GRAPE JUICE and WINE

The effect of pasteurization on the microbiological and sensory quality of white grape juice and wine was investigated. Heat treatment of less than 3 Pasteurization Units (PUs = minutes at 60°C or equivalent) was sufficient to reduce 106 cells/mL of Saccharomyces cerevisiae and Hansenula anomala added to Chenin blanc juice to an undetectable level. In contrast, heat treatment exceeding 105 PUs was required to have a measurable browning effect on juice, as measured by absorbance at 420 nm and by formation of 5-hydroxymethyl-furfural. Furthermore, up to 50,000 PUs did not significantly affect flavor, as determined by duo-trio tests with 18 trained judges. Pasteurized (23 PUs) and nonpasteurized juice fermented at the same rate, although not as rapidly as pasteurized, thiamine-supplemented juice. Tunnel pasteurization (13.7 PUs) reduced 5 × 106 yeast cells/mL added to grape juice to an undetectable level and did not significantly affect juice or wine flavor.

Biological Assay of Nitrogen Content of Grape Juice and Prediction of Sluggish Fermentations

A bioassay based upon final culture absorbance was developed and utilized to estimate nitrogen content of grape musts. Amino acid analyses of grape musts were run for comparison to the values obtained from the bioassay. In Chenin blanc and French Colombard musts, there was a good correlation between nitrogen content as measured by biomass yield with that determined from amino acid analysis. The nitrogen content of Grenache musts showed a positive correlation with cell yield in the bioassay, but was not as strongly correlated as in the other two varieties. The amino acids generally recognized as good yeast nitrogen sources were more highly correlated with biomass yield than were poorer nitrogen sources. Ammonium ion supplementation of nutrient-deficient Chenin blanc juices either stimulated fermentation rate or had no effect, depending upon the juice. Ammonium utilization was found to be dependent upon the pH and ethanol concentration of the medium. Fermentation of nitrogen deficient musts was found to be stimulated by a variety of growth factors in addition to nitrogen.

Heat Tolerance of DormantVitis viniferaCuttings

Cuttings of one-year-old <i>Vitis vinifera</i> canes of cvs. Cabernet Sauvignon, Merlot, Chardonnay, and Chenin blanc were treated at temperatures between 50°C and 60°C for time periods up to 30 minutes to determine their heat tolerance. Survival was estimated by visual observations of shoot and root development of cuttings in the greenhouse after four to six weeks. All cultivars had survival rates equal to controls when treated at 54°C for 30 minutes. Treatment of samples above 54°C revealed seasonal and cultivar variability in heat tolerance. Maximum heat tolerance is significantly higher than previously reported. These data indicate that dormant cuttings of <i>Vitis vinifera</i> are capable of surviving extended periods of heat treatment that may be essential for eliminating <i>Agrobacterium tumefaciens</i> (Smith and Townsend 1906) Conn 1942 biovar 3, the crown gall bacterium during asexual propagation.