Issue link: http://winesandvines.uberflip.com/i/643683
March 2016 WINES&VINES 29 WINEMAKING can ferment easily on glucose to the virtual exclusion of any other carbon source. Upon induction to the [GAR + ] state (induced general- ist), they switch to using a much wider array of carbon sources. However, within any population of a specific strain of yeast, there is a certain percentage that naturally switch at any time. In grapes there is a mixture of glucose, fructose and other simple sugars. Since yeast prefer feeding only on glucose, that is where the initial growth starts. In any natural popula- tion of S. cerevisiae, a small percentage of that population is capable of fermenting fructose. That population segment can multiply during any given fermentation, so that at the end of a fermentation all the fructose is consumed, leaving only glucose as a food source. If the proper bacteria were present, they could exac- erbate the [GAR + ] state, increasing that per- centage of the yeast population. With the other simple sugars exhausted and leaving only glucose, the yeast metabolic systems are inca- pable of switching back soon enough to take advantage of this food. The result is a stuck fermentation. Importantly the yeast are not dead, just not able to grow vigorously. Back to the beginning So how does this relate to my client's fermenta- tion? The client knew his fermentation was stuck. It had not responded to the normal buildup of other yeast nutrient additions and cultures. The lots of wine must have had some population of Lactobacillis/Pediococcus organ- isms in the mixture that induced the [GAR + ] state in the fermentation, and the fermentation slowed to a crawl. The client, seeing the fer- mentation sticking, added lysozyme to the fermentation, which wiped out the gram- positive bacteria so that the gram-positive bacteria and yeast could not take advantage of and consume any remaining sugar. The yeasts were weakened by [GAR + ] and had not reverted to [gar - ], so they could not effectively use the low amounts of glucose remaining to finish fermentation. This is when I received the call to solve the issue of why the fermentations wouldn't com- plete. The one nutrient that was not added was oxygen. As my first test, I used the fermenta- tion that had the greatest amount of sugar remaining. This wine had started at 23° Brix at harvest, and now, using a hydrometer, it measured 1.8° Brix. In order to add oxygen to the wine, I used a Parsec Oxygenious. After about three days, the sugar level fell by 0.1° Brix. It continued to fall at the same Decades of experience, know-how and innovation are evident in the quality construction of all of our presses, resulting in many years of reliable performance. Open and Dual Presses also available. Your advantages of a closed press system: Sealed door (option) Gentle pressing Large dejuicing area, unique channel design Juice outlet fittings can be closed for fermentation or maceration time Easy cleaning of the interior press drum and the removable drain channels FOR THE LOVE OF WINE THE NEW EUROPRESS TANK PRESS ı-320 hl T24 with sealed door West: 707-864-5800 East: 540-825-5700 info@euromachinesusa.com – www.euromachinesusa.com SWITCHING RATE TUNED TO ECOLOGICAL NICHE vs. Low [GAR + ] switching frequency Simple carbon sources Monoculture High [GAR + ] switching frequency Complex carbon sources Diverse microbial communities DANIEL F. JAROSZ7 ET AL., UCSF / CELL JOURNAL