Yizheng Huang VEN 124 Midterm II

TOPIC 1

Based on background information, there had 54 once-­‐used Chardonnay barrels and less than half of them suffered an arrested fermentation; approximately 24 barrels were still fermenting after three weeks fermentation, which means they were suffering a sluggish. Logically speaking, at a high possibility, 24 barrels that suffering a sluggish fermentation are all fermented from once-­‐used Chardonnay barrels. Also, it is notable to realize that fermentation may suffer a sluggish or protraction, even though it reaches dryness eventually. (Kunkee 1991) Thus, we can assume that 54 Chardonnay barrels may more or less suffer a sluggish. More information is required to collect to prove this assumption. The functions of over charring of barrel are not clear so far. More research is necessary to figure them out.

Two obvious mistakes should incur attentions. Firstly, inoculation with commercial yeast in winemaking is 106 cells/mL instead of 105 cells/mL indicated from background information. (BOULTON et al. 1995) Insufficient growth of yeast will significantly lead to a sluggish fermentation. Secondly, based on model fermentation, the sugar contents start at 22 to 24 Brix (BOULTON et al. 1995); however the winery instructs a start Brix at 27.8. A high content of sugar will incur large amount of alcohol produce in fermentation. Alcohol significantly inhibits the metabolism of yeast, leading to a sluggish—Ethanol Toxicity. Excess ethanol affects the viability of yeast cells on the fermentation capacity. (BOULTON et al. 1995) Also, high content of ethanol is able to inhibit the amino acid transporter function and increase the passive proton flux, further affect the nitrogen compound utilization.

It is impossible to fully sterilize the once-­‐used Chardonnay barrels so that most possibility is shown that some inhibitory microbes reserves in the lees after a prior fermentation of Chardonnay, which would significantly influence the Chenin black fermentation afterwards. A reserve of wild Saccharomyces can produce K2 toxins, which inhibit the normal growth of commercial yeast strains, leading to a sluggish. (Young 1987; van Vuuren and Jacobs 1992) What’s more, other microorganisms can produce organic acids, fatty acids. Those of acids are able to inhibit a normal metabolism