Reducing Bitterness In Wines. The effect of wine composition, sample evaluation method and salivary flow on sourness, bitterness and astringency

The effect of method of sample evaluation on sourness, bitterness and astringency was explored in water and in wine. The temporal responses using “sip and spit” procedure (the normal lab protocol) were compared to the TI responses when samples were sipped and swallowed, more similar to actual consumption method. With the exception of astringency in wine, no differences between the two methods were found. When samples were swallowed, astringency intensity was slightly lower and the total duration of astringency was slightly shorter, than when the samples were expectorated. However, considerable variation among judges occurred in this very small number of judges, thus this effect is not be concluded to significantly affect perception based on this preliminary study. To explore the effect of rate of salivary flow on TI perception of these three attributes, sourness, bitterness, and astringency were evaluated using expectoration. No significant differences were seen among flow groups, in contrast to a previous study in which high flow judges tended to have a shorter persistence of bitterness or astringency than low flow judges. To determine if any real effects of salivary flow occur, a larger number of subjects needs to be examined and a method for standardizing their sensory ratings over times must be found. Bitterness and astringency of epicatechin and catechin, the monomeric isomers (flavan-3-ols) of the phenols found in wine, were evaluated by both scalar and temporal methods (TI). By both, epicatechin was shown to be more intensely bitter than catechin, and by TI, bitterness lasted longer for epicatechin than catechin. While no difference in astringency was found by scalar tests, by TI, at higher concentrations, epicatechin had higher maximum astringency and longer duration of astringency than catechin. Both compounds were more bitter in 5%ethanol than in water, although the astringency did not vary significantly. The implications of these results for predicting wine flavor are unknown. On-going research in our lab is addressing differences in the tastes and intensities of different polymers of these two compounds in wine.

Factors Affecting Sugar Utilization and Fermentation

The quantity as well as quality of available nitrogen during fermentation of grape juice appears to affect the rate of fermentation. If too high, rapid fermentation occurs generating excessive heat that may pose a problem or require temperature control. If too low, nitrogen limitation will result in a sluggish or even stuck fermentation. The site of control of fermentation rate is uptake of the sugar into the cell. Sugar uptake is mediated by specific transport proteins located in the plasma membrane at the cell surface. Five glucose transporter genes have been identified in my laboratory. The role of each of these genes in anaerobic grape juice fermentation is being analyzed. Simultaneous loss of two of these genes (SNF3 and HXT1) resulted in a yeast strain completing grape juice fermentation under conditions where the wild type parental strain yielded a stuck fermentation. This finding has important implications for the genetic engineering of a yeast strain for wine production that will be less likely to stick or fail to complete fermentation. In addition, it was found that adenine concentration can be stimulatory to fermentation increasing the maximum fermentation rate and decreasing overall time to dryness. The adenine effect was not a simple consequence of extra nitrogen, as supplementation with the same or higher levels of non-adenine nitrogen compounds did not result in the same stimulation. However, the adenine effect was both strain and temperature of fermentation specific. There was a greater effect with Montrachet than with Prise de Mousse or Pasteur Champagne, and a greater effect at warmer temperatures (20 versus 15°C). The effect of timing of addition of adenine on fermentation performance was complex, requiring additional studies to evaluate properly.

Ethyl Carbamate Formation by Malolactic Bacteria

Arginine is one of the major amino acids found in grapes and wine. Certain strains of malolactic wine lactic acid bacteria can degrade this amino acid with the formation of ornithine, carbon dioxide and ammonia. The degradation of arginine by two strains of malolactic bacteria, Leuconostoc oenos MU2 and Lactobacillus buchneri CUC-3, was investigated to assess the potential formation of ethyl carbamate precursors in wine. Both strains degraded arginine and surprisingly, excreted citrulline, a known precursor of ethyl carbamate. The excreted citrulhne reacts with alcohol to form substantial amounts of ethyl carbamate with heat treatment (71°C/48 hours). The formation of ethyl carbamate correlated well with arginine degradation and citrulline production. From a winemaking point of view, the production of citrulhne is a problem, since it can react with alcohol over time to form ethyl carbamate even at low storage temperatures. However, only very small amounts of ethyl carbamate were formed without heat treatment (<10 ng/g or ppb). 7-1 Our results show that malolactic bacteria can indeed be a potential source of ethyl carbamate precursor (at least citrulline). Thus, care must be exercised in selection of starters to conduct malolactic fermentation in wine. Ideally, those strains unable to degrade arginine should be chosen in order to minimize precursor formation. In addition, spontaneous malolactic fermentation by undefined indigenous strains should be discouraged, as this may result in formation of ethyl carbamate precursors.

An Appraisal of Liquid Chromatography-Mass Spectrometry for the Analysis and Tracking of Wine and Grape Components-Extension

The consumption of wine may explain the unaccountably low rate of heart disease in parts of France. This suggests a cardioprotective effect for wine. One theory to explain this phenomenon is that the phenolic antioxidants found in wine inhibit LDL lipid oxidation, the initial stage of atherosclerosis. Wine antioxidants are more potent than vitamin E (known to reduce heart disease) in preventing LDL lipid oxidation, supporting this theory. The amount of these phenolic antioxidants in two glasses of wine could significantly increase the total levels of these compounds in the American diet. Phenolic antioxidants like those in wine have also been shown to reduce cancer rates and, in-vitro, inhibit many basic mechanisms of carcinogenesis. Further studies are needed to establish a causal link between wine consumption and disease prevention. Analyses of Wine Components that May Reduce Disease Our results this year were quite satisfactory. Our first success was developing an analytical procedure for the analysis of resveratrol by HPLC. This procedure was accepted for publication in the Journal of Agricultural and Food Chemistry Resveratrol is one wine component which has been implicated as a anti-atherosclerosis compound. As part of the study to develop a procedure we analyzed for resveratrol in a dozen California wines and found higher levels in Pinot noir than Cabernet Sauvignon and Zinfandel. Our large scale analysis now underway will tell whether or not this is a real trend. A study that is directly relevant to the health effect was carried out by studying the anti-oxidant capacity of wine phenolics. As mentioned above, it is the property of being an antioxidant, that is most likely to be the key to any health benefit from wine. In the experiment we carried out, we tested the ability of these wine antioxidants to prevent the oxidation of human LDL lipids. It is this event, the oxidation of LDL lipids, that is supposed to lead to atherosclerosis, the cause of most heart disease mortality. Thus, anything that prevents the oxidation from occurring is a candidate for preventing heart disease.

Alternatives to Bentonite

Use of bentonite as a protein stabilizing agent for wine generates significant lees and results in the loss of flavor or aroma characteristics. An alternative to bentonite such as acid protease treatment would not lead to significant lees nor would non-proteinaceous materials be affected. The biochemical characteristics of proteins leading to haze formation are not yet known. Haze could result as a consequence of insolubility due to proteins with isoelectric points at or near the pH of wine, or to hydrophobic interactions among denatured proteins. Ethanol may reduce the solubility of glycosylated proteins. Ethanol also results in loss of solubility of polysaccharide material, also causing a haze. Hazes may arise for different reasons in different wines. Proteins of varying isoelectric points as predicted from retention time on ion exchange chromatography can lead to haze in wine. This was determined from an analysis of the protein composition of the haze material as well as from analysis of the haze forming potential of proteins separated from wines then subjected to heat treatment. Proteins with an isoelectric point near to the pH of wine were previously thought to be largely responsible for haze formation. Earlier results from our laboratory agreed with this finding. However, our studies of this past year suggest otherwise, but need to be confirmed using other juices. It is likely that the factors leading to haze formation vary depending upon the juice and seasonal variation. In any event, haze formation is a complex chemical process.

Alternatives to Bentonite

There are many causes of hazes in wine and two predictive tests: heat and ethanol. In our experience, ethanol-induced hazes are largely polysaccharide while heat induced hazes are proteinaceous. The protein profiles of numerous experimental and commercial wines were compared using HPLC at differing stages of bentonite treatment. Soluble proteins remaining in the wine, following heat treatment were also analyzed. Distinct HPLC peaks were associated with heat-haze. Total protein was not correlated with either heat or ethanol haze in agreement with many previous studies. Fermentation of Chardonnay in the presence of bentonite reduced requirement for bentonite in one wine, but had no impact on a second. Excessive bentonite treatment increased subsequent heat haze in some, but not all wines tested, in agreement with commercial winery observations.

Capture and Utilization of Fermentation Emission

SUMMARY AND RESEARCH ACCOMPLISHMENTS: Preliminary results indicate that although there is indeed an increase in the aroma/bouquet of the wines whose volatiles have been added back, some of the panelists agreed in that “the increased aroma and bouquet do not necessarily translate into an increase in quality of the wines.” This was particularly true for white wines fermented at 80 deg F compared to those fermented at ’55 deg F.

Investigation of the Chemical and Biological Changes Identified with Sur Lie Treatment of Wine

The following summary is taken from the Technical Abstracts for the oral presentation given by Greg La Follette at the Annual Meeting of the American Society for Enology and Viticulture, 1991. This work comprises his Master’s Thesis research. During the 1989 and 1990 vintages, we examined wines from two commercial wineries. Sur lie wines (with extended yeast lees contact) were compared to wines racked immediately after fermentation. Sixty gallon stainless steel and oak barrels were used with the same juice to produce identical wines except for yeast contact and stirring. Samples taken monthly and at bottling revealed no differences in dissolved oxygen in the barrel, time for completion of malolactic fermentation cell viability, redox potential, viscosity, protein stability, fining requirements, pH and concentrations of protein, sulfur compounds and acetaldehyde. Results of diacetyl content and extent of browning were mixed. Racked wines were lower in phenol and total nitrogen concentrations. In the 1990 vintage, acetaldehyde was initially lower in sur lie wines; this difference diminished with time. Sensory analyses of bottled wines using the forced-comparison pair test showed no differences in oak aroma, while toast aroma was higher in sur lie wines. Results of butter and fruitiness as aroma descriptors depended on containers used: in oak, sur lies wines were less buttery and more fruity in aroma than racked wines; in stainless steel, racked wines were more fruity, with no differences in buttery aroma. With descriptive analysis, only apple and pineapple characteristics and spiciness were different. “Mouthfeel” components snowed no differences.

Control of Current and Emerging Problems of Microbiological Spoilage of Wine

Reports have been received from California winemakers in recent years of new types of microbial spoilage problems in both stored and bottled wines. The responsible organisms, not normally associated with wine, are represented by species of the following yeast genera: Zvaosaccharomvces. Pichia. Hansenula, Kloeckera. and Debarvomvces. and_ by species of the following bacterial genera: Acetobacter. Bacillus. and especially vigorous strains of Lactobacillus. There is also continual concern over the apparent ubiquitous presence of Brettanomyces and Dekkera.

Interaction of commercial wine yeasts and malolacric bacteria

Twenty-nine strains of malolacric bacteria and forty-three strains of wine yeasts have been obtained and placed in the departmental culture collection as source material for this project. Nine diffusion type assays for screening yeast/bacterial interactions have been examined using various media preparations. For yeast strain influences on lactic acid bacteria, the Circular Surface Inoculation using a dilute grape juice medium has already shown some antagonistic relationships with the few strains tested. Unfortunately, the Circular Surface Inoculation Assay may not prove to be satisfactory for determining the influence of LAB producer strains on yeast target strains as the yeast grow too rapidly and develop a lawn before LAB growth occurs.