Reducing Bitterness in Wines

As reported previously (Noble, final report, AVF 91), astringency and bitterness of 18 wines, varying in ethanol (1, 8, 14%), pH (3.0 and 3.6) and added phenolics (none or 1500 mg/L catechin or tannic acid) were evaluated by time-intensity (Tl) methods. Using this procedure, the wine is ingested and perceived intensity is rated continuously Increasing ethanol concentration dramatically increased both the intensity and duration of bitterness and area under the Tl curve, while having very little effect on any astringency. Addition of tannic acid dramatically increased bitterness and astringency intensity and duration, more than addition of an equivalent amount of catechin. Raising pH from 3.0 to 3.6 had virtually no effect on bitterness but decreased astringency intensity and duration. As reported herein, salivary flow was collected in response to the same wines. The largest increase in production of saliva was elicited by decrease in pH (increase in TA); tannic acid, which elicited intense astringency, had the next largest effect, followed by increase in ethanol. Examining the taste responses of the judges, grouped by salivary flow rate, showed that (pooled over all samples) low-flow judges perceived bitterness and astringency more intensely and longer than high-flow individuals. The effect of method of sample evaluation on sourness, bitterness and astringency was preliminarily explored in water and in wine. The temporal responses using “sip and spit” procedure (the normal lab protocol) was compared to the Tl 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. For evaluation of astringency, when samples were swallowed, astringency intensity was slightly lower and the total duration was slightly shorter, than when the samples were expectorated. However, considerably variation among judges occurred , 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 Tl perception of these three attributes in water and in wine, data for the expectorated samples was analyzed for low, medium and high flow subjects for each samples. Inconsistent differences were seen across flow groups, further, by analysis of variance problems with reproducibility were encountered. In contrast to the previous study, here high flow judges tended to have a longer persistence of bitterness or astringency than low flow judges. These low-flow-judges rated the samples higher in both attributes, consistent with the above study. Because of the inconsistent responses of judges, we have repeated the experiment in wine to determine if any real effects of salivary flow can be determined. Twenty judges rated the intensity of sourness, bitterness and astringency in wines by time-intensity methods following extended training. These results, while not demonstrating a large influence of salivary flow on perception were more consistent with the first study. Although the results are still being analyzed statistically, preliminary analysis across all judges indicates that the data are reproducible across replications and that significant differences among samples for each attribute were found for all Tl parameters. While neither concnetration nor salivary flow rate affected the time-to maximum, maximum intensity and total duration increased significantly between samples. Although very small differences in maximum intensities were found among flow groups, the subjects with the highest flow rates, perceived all three attributes for the shortest duration.