In this current grant year, it was discovered that some of the variability in response to phenolic compounds displayed by different commercial strains was possibly due to subtle differences in preparation of the synthetic juice medium, Triple M. This was confirmed using slightly different protocols and the Premier Cuvee yeast strain. Therefore, the preparation and composition of this Medium has been redesigned this year in order to avoid this problem. Analysis of the impact of phenolic compounds is continuing. To date, gallic acid appears to be uniformly stimulatory at concentrations found in wine while ferulic acid may be neutral, stimulatory or inhibitory to sugar consumption under laboratory conditions mimicking natural fermentations. The hexose transporters encoded by the FDTT9/HXT11 genes that are under multidrug resistance control were shown to be expressed under enological conditions. The presence of these genes has been shown to be stimulatory for the uptake of inhibitory drugs. They may therefore play a role in uptake or release of phenolic compounds inside of the cell by coupling such movements to the uptake of glucose. In this current grant year, we launched the comparative analysis of the impact of phenolic compounds on different yeast strains (conducted by Laura Lange). She initially found that the effects were quite variable and there appeared to be no consensus as to whether the effects of a given compound were stimulatory or inhibitory with the exception of gallic acid. In the course of her work, we discovered that the inherent variability in the composition of the Triple M medium led to variation in the response of the yeast. The pH of this medium is adjusted using ammonium hydroxide. We found that since the pH of our water supply varied, so did the ammonium content of the medium. Further analysis revealed that this difference in nitrogen content was not impacting the results. However, the medium has been redesigned to contain a constant concentration of nitrogen. Another problem with the medium was the low concentration of potassium. Previous work in my laboratory indicated that potassium deficiency could lead to a sluggish fermentation and that this effect was somewhat strain dependent. We therefore decided to use potassium hydroxide to adjust the pH of the medium to assure a reasonably high concentration of potassium. Finally, the micronutrients were prepared as a stock solution and diluted when added to the medium. We noticed that a precipitate formed in the stock upon storage and that the age of the stock solution was correlated with variability in the effect of the phenolic compounds. This makes sound physiological sense since the cofactors derived from the vitamins and minerals in this mix are critical for respiratory activity of the yeast. To eliminate this problem, we now make the micronutrient cocktail fresh each time and use the Triple M medium within 48 hours of preparation. This has eliminated the variability in the response. This important optimization of the medium slightly delayed progress on the grant, but we are now conducting the comparative studies across strains. This will not be finished as originally hoped by the end of this grant year, so will continue into the first three months of the next grant year.

Astringency has been shown to have carry-over effects which influences the perception of astringency of red wine and astringent compounds. To quantitatively measure this effect, trained judges rated intensity of astringency continuously while repeatedly sipping wine. When red wines were sipped 4 times at 25 second intervals between sips, the astringency intensity increased significantly with each sip. At each sip, astringency increased, reached a maximum intensity about 15-16 seconds after the sip was taken, then decreased slowly until the next sip was taken and again astringency increased. For two of the wines the increase with each sip was significant, whereas the other two the increase in astringency between the 3rd and 4th sip was not significant. To see what happened when more sips were taken, astringency was continuously rated over 8 sips for alum and tannic acid. The 4th sip of tannic acid was not more significantly intense than the 3rd , although the astringency continued to slowly rise. The practical consequences of these results are that most evaluations of red wines are rendered invalid due to the carry-over phenomenon demonstrated in this study. Astringency of red wines evaluated either by a winemaker during winemaking or for blending or by wine show judges is influenced by the wines tasted before it. To quantify the effects of physiological differences on perception of astringency the saliva flow rates of the judges in the red wine and alum/tannic acid studies above were determined. Individuals with low flow rates of saliva perceived astringency of red wine and of the alum and tannic acid more intensely and longer than high-flow subjects. This physiological difference in perception of astringency is of great significance in understanding how astringency is perceived. Since saliva flow rate varies with the size of the person generally speaking, the practical value of this information may lie in marketing wine, where it may account for preferences of “smaller” consumers. In evaluations of the viscosity of saliva-tannin mixtures, it was shown that viscosity of saliva decreases when tannin is added, analogous to sipping red wine. This is consistent with the observations of the effect of salivary flow status. If astringency is felt as the friction resulting from precipitation of saliva proteins by tannins, than high-flow subjects can restore lubrication better and hence perceive lower levels of astringency than low-flow individuals.

Over 25 wines were fermented on -20 scale using Cabernet Sauvignon grapes from four different vineyards in California. For each vineyard, a control fermentation was compared with treatments employing maceration treatments including oak extract addition, extended maceration, heat at the end, color enzyme addition, and rotary fermentation. All wines were analyzed for phenolic composition by several different assays. Many of the treatments had small or variable effects, but heat at the end appears to consistently increase phenolic levels. Wines from this and the previous years’ experiment will be offered for tasting at an event in the winter of 2001.

Twelve 1998 Cabernet Sauvignon wines have been obtained from wineries (with minimal oak contact) to select those perceived to be “hard” and “soft”. Winemakers have been interviewed in an attempt to define how each makes the judgement. Although ‘hard” or “soft” are customarily defined by mouthfeel, the contribution of other wine sensory properties is not known. These factors could include color, the aroma and flavor of the wine. More subtle, yet important, we do not know how each individual integrates the perception of taste and mouthfeel. Ten winemakers participated in a “sorting” test in which they were asked to taste the 12 wines and group them on the basis of their perceived similarity. The wines were served in dark beakers, so no information from smell or color was available for this task. Each winemaker used his/her own criteria for the grouping. (For these tests, dark glasses were used to remove color cues). Students at UCD did the same similarity sorting tasks and then were trained for time-intensity (TI) studies in which the intensity of each attribute was rated continuously over time. For each wine, the trained judges took one sip of wine and initiated rating intensity; at a prompt they swallowed the wine, then 25 sec after the first sip, they took a second sip, while continuing to rate the intensity. The procedure of rating for two successive sips was used to include the carryover effects that occur under standard tasting conditions in which several sips are taken, without rinsing. Bitterness, astringency and sourness were evaluated in duplicate, using blue glasses and testing under red light.