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60 p r a c t i c a l w i n e r y & v i n e ya r d a U G U S t 2 0 1 4 P roducing high-quality wines can be difficult even when Mother Nature cooperates and grapes arrive at the winery in pristine condition. However, in some years events occur that thwart the efforts of even the most vigilant and skilled vine- yard manger in producing ripe and undamaged fruit. Rain close to harvest can produce con- ditions perfect for the growth of Botrytis, while damage from heavy rain or hail provides opportunities for organisms both large (fruit flies) and small (bacte- ria and yeast) to proliferate and cause spoilage. Although Botrytis damage itself can be detrimental to grape quality, secondary issues created by damage to the grape skin can also be significant. The large array of microorganisms present on the grape berry surface typically have little impact on grape and wine quality. How- ever, if the integrity of the grape berry surface is compromised through rain/ hail damage or Botrytis infection, then rapid growth of oxidative yeast and ace- tic acid bacteria can occur. For example, the acetic acid bacteria Acetobacter and Gluconobacter are typically present in low populations (below 10 2 cfu per mL) on healthy berries, while their populations can reach more than 10 5 cfu per mL on damaged or Botrytis-infected grapes. Gluconobacter species are com- monly isolated from grapes and must but disappear as alcoholic fermentation begins, while Acetobacter are more etha- nol-tolerant and may survive through alcoholic fermentation. The main spoilage issue associated with these bacteria is excessive produc- T E C H N I C A L R E S O U R C E F O R G R O W E R S & W I N E R I E S practicalwinerylibrary.com Access Practical Winery & Vineyard article archives online. 63 White wine aroma optimization By Karien O'Kennedy, Maryam Ehsani, Peter Salamone 70 Sonoma County — Improving pest management practices By Nick Frey James Osborne, extension enology specialist, Oregon Wine Research Institute, Food Science & Technology Department, Oregon State University BY Dealing with compromised fruit in the winery Photo by VAugn WAlton (oregon stAte uniVersity) Grape cluster with cracking and fruit flies. Photo by WAlt MAhAffee (usDA-Ars) Grape cluster with bunch rot (Botrytis). W I N E G R O W I N G