Phenolic and Sensory Evolution of Wines from Oxygenation (2017)

This study examines the effect of oxygenation on wines. Cabernet Sauvignon grapes were harvested and, after completion of fermentation, wine was drained and pressed into two tanks. One tank was a control, and one tank received 40 mL Oxygen/L wine/month for 3 days, and this rate was then halved every 3 days until after malolactic conversion began, where it received micro-oxygenation at 0.5 mL Oxygen/L wine/month. A third set of grapes from the same block were picked 5 days later (after a large rain event), and then received flash détente. Since malolactic conversion completed so quickly for this treatment, its oxygenation could only be at 40mL Oxygen/L wine/month for three days after draining and pressing before switching to 0.5 mL Oxygen/L wine/month. The treatments between the control and oxygenated wines were similar, but the vinification of the flashed wine was different, marked by 10 days of fermentation (compared to 14 days for the other treatments, including a 3 day cold soak). The flashed wine also had slightly different additions made. No major differences are found in wine chemistry between the control and oxygenation treatment, except for slightly higher lactic acid in the treatment. The flashed wine had higher acidity, possibly due to differential tartrate adds. The oxygenated wine had higher rates of S. cerevisiae and several Lactobacillus species relative to the control, but lower acetic acid bacteria. The flashed wine had much lower levels of acetic acid bacteria and Lactobacillus, and lower levels of S. cerevisiae as well. However, it was higher in O. oeni. Color intensity lowered among the wines from November to April; however, the oxygenated wine may have had a slight increase in color intensity relative to the control over this time (although this was weak). The oxygenated treatment had higher color intensity than the control, and the flashed wine was highest. Phenolic parameters generally decreased from November to April, and oxygenation did not appear to have much effect on the phenolic parameters. The flashed wine was much higher in catechin and quercetin and was also higher in tannin. Although it was initially lower in anthocyanin (and higher in polymeric pigment), it ended up being higher in anthocyanin.

For the triangle test, of 26 people who answered, 12 people chose the correct wine (46%), suggesting that the wines were not significantly different. In general, people who answered correctly tended to prefer the oxygenated wine, although the preference trends were somewhat complex. For the descriptive analysis, there was a strong trend for the flashed wine to have higher overall aromatic intensity than the other wines (LSD=0.97). There was a slight trend for this wine to have higher Fruit Intensity and Body, and perhaps slightly lower Herbaceous/Green character (although it was similar to the oxygenated wine in this regard). The control wine tended to have higher Herbaceous/Green character, lower Overall Aromatic Intensity, and higher Astringency (although equal to Flash in this regard). The oxygenated treatment tended to have lower Bitterness and Astringency, and perhaps lower Body as well. More studies should be performed on oxygenation, with regard to timing, amount, and with regard to continuous vs discontinuous oxygenation.

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The Impact of Bloom Leaf Removal vs Veraison Leaf Removal (2017)

This study examines the impact of leaf pulling at either bloom or at veraison. The goal was to have looser clusters and smaller berries from pre-bloom leaf removal. A block of Cabernet Sauvignon (planted 2006) was divided so that every other row was a different treatment. One row had the four-most basal leaves removed at 30% bloom (mid-May), exposing the entire fruiting zone. Continuous passes were made to ensure fruit zone exposure throughout the season. Every other row had leaves removed at the start of veraison, in mid-August. Grapes were harvested and processed at the same times, and all other vineyard and winemaking treatments were identical between treatments. Each wine received a 6-day cold soak, and 25 days of total maceration. Grapes from prebloom leaf removal had lower TA, malic acid, and tartaric acid, with a similar pH to the control. Tannin was higher in grapes with pre-bloom leaf removal, but anthocyanins were lower. Pre-bloom wine chemistry was similar except for slightly lower acidity. Color intensity and tannin was also slightly increased in the pre-bloom wine, although these differences were not very pronounced. For the triangle test, of 19 people who answered, 6 people chose the correct wine (32%), suggesting that these wines were not significantly different. In general, of those who answered correctly, no preference trends could be seen between wines. For the descriptive analysis, there were no strong trends for the descriptors used in this study. Most descriptive results were mixed, but Pre-bloom leaf pulling may have had slightly lower Acidity and higher Body. It also may have had slightly less Herbaceous/Green  character, but these trends were weak. These results suggest that pre-bloom leaf removal may not always have as large of an impact as is often seen. This practice should be performed more at different sites, on different varieties, and in different vintages (perhaps rainier vintages which may benefit more from this kind of leaf pulling regimen). 

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The Effect of Directly Processing Fruit after Harvest vs Processing after Refrigerating in Cabernet Sauvignon (2016)

This study examines the impact of directly processing fruit after harvest compared with harvesting fruit after it has been refrigerated overnight.  Cabernet Sauvignon grapes were picked from the same block on the same day and were either destemmed into T bins on the same day of harvest or refrigerated overnight before processing the next day.  All other treatments were identical.  The grapes which were refrigerated overnight exhibited slight increases in color intensity, but otherwise no major chemical differences could be found between treatments.  Overall, the wines were not found to be very different.  Very few differences could be seen with descriptive analysis.  These results suggest that refrigerating overnight prior to processing may not have any detrimental effects on finished wine quality.  However, this study should be repeated multiple times, with several different kinds of grapes as well as different levels of grape quality and cleanliness.

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The Effect of Leaf Removal at Bloom vs Leaf Removal at Veraison on Ripeness (2016)

This study examines the impact of removing the 4 most basal leaves from Cabernet Sauvignon vines at 30% bloom. One section of a vineyard block was not leafed at bloom, while another section underwent this leafing treatment. Both treatments received leaf-pulling at veraison. All other vineyard and fermentation practices were the same. Leaf removal at bloom appeared to slightly reduce berry weight, cluster weight, Brix, and yield. Grape phenolics and TA were slightly increased by bloom leaf removal. Wine produced with leaf removal at bloom had lower ethanol, color intensity, and tannin. Judges did not find the wines to be significantly different, and there were no strong preference trends for either wine. Early leaf removal may have had a very weak tendency to increase Overall Aromatic Intensity. The lack of differences are likely due in part to the particular vintage (weather events may have equalized the treatments) and in part due to vegetative growth reducing the effectiveness of the bloom leaf removal. More studies need to be performed in this area in order to draw more conclusions.

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H2S Production by Different Low-H2S Producing Yeast Strains (2016)

This study examines the effect of different low H2S-producing yeast strains on the sensory attributes of Cabernet Franc and Cabernet Sauvignon Rosé. The grapes were harvested on the same day, pressed together, and after settling was racked into four different 484L puncheons (2006 Hungarian oak from the same cooper). The barrels were inoculated with the following yeasts: Rhône 4600 (ScottLabs), Allegro (Phyterra), Sensy (ScottLabs), and Fermol Elegance (AEB). Rhône 4600 is not marketed as a low H2S-producing yeast strain and was intended to act as a soft control. The strains showed similar fermentation kinetics except for Rhône 4600, which was markedly slower. Additionally, the wine produced by Rhône 4600 had a higher alcohol content and higher total SO2, possibly from yeast production. The sulfide contents of the wines, however, were essentially indistinguishable. No strong trends were found with the descriptors used for this study. Rhône 4600 tended to show higher Fruit Intensity and Overall Aromatic Intensity. Many of these wines were perceived as slightly reduced. In general, people tended to prefer wines produced with Rhône 4600 and Allegro yeasts.

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The Stylistic Impact of Malolactic Conversion on Cabernet Sauvignon (2016)

This study examines the stylistic impact that malolactic conversion has on Cabernet Sauvignon. Two lots of Cabernet Sauvignon wine were pressed and combined into one tank. A portion of this wine was sequestered in carboy in order to not undergo malolactic conversion. The portion in the tank was inoculated with Lalvin Elios Malolactic Bacteria. The control wine was sulfured in order to prevent natural malolactic conversion from occurring. The results show classical malolactic conversion results, with a decrease in TA and malic acid and increase in pH, lactic acid, and VA. The slight decrease in anthocyanin and tannin is also typical of malolactic conversion. If the wine made with malolactic conversion had been sulfured, it would likely show lower color intensity as well. Sensory analysis found the wines to be significantly different (p<0.05). These wines were voted to have an average degree difference of 4.8 (out of 10), suggesting that the wines were moderately different. There was no major preference trend for the wines in this study. Comments on this study were mixed. There were no strong trends for the descriptors used in this study. In general, the wine with no malolactic conversion tended to show higher Astringency, lower Body, and (surprisingly) lower Acidity. The effect of malolactic conversion on the fruit aromatics, as well as on green and herbaceous qualities, seemed complex and merits further attention.

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Hand vs. Mechanical Harvesting with Cabernet Sauvignon (2015)

Machine and hand-harvested Cabernet Sauvignon were compared for chemical, phenolic, and sensory differences.  The machine harvested wine had higher titratable acidity and lower pH, but had less anthocyanin.  However, color intensity and hue were similar between treatments.  The sensory attributes of the wines were significantly different, with most people preferring the hand-harvested wine.  This is likely due to a Brettanomyces infection in the machine-harvested wine.

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