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w i inneeGM A K IN GG w R O WIN over microbial competition, yet remain more viable over time. Acetic acid, along with toxins that at least some species produce, is inhibitory to Saccharomyces, and the fermentation may stick. While Oenococcus is hetero-fermentative and thus theoretically could cause this type of spoilage, in fact Lactobacillus is overwhelmingly the bacterium responsible. Lactobacillus spoilage may go undetected until too late. Because Lactobacilli do not make ethyl acetate, there is no telltale odor, and sugar can mask the acetic "bite" at the finish. Culturing is not recommended because wine Lactobacilli tend to grow very poorly in culture. PCRbased tests detect certain lactic acid bacteria, but do not detect all wine Lactobacilli and thus miss incidences of spoilage which could have been observed microscopically. Microscopic examination easily determines whether Lactobacilli of any species are growing. If there are enough cells to cause a problem, there will be a large enough population to see. Chemical tests can alert the winemaker to check for Lactobacillus spoilage: pH rise, drop in malic or rise in lactic acid, and rise in VA/acetic acid. STUCK WINES Microbes to watch out for: Lactobacilli, Pediococcus, Acetobacter, Brettanomyces, surface film yeast Danger signals: CO2 production, spontaneous MLF, VA rise, film on surface Monitoring methods: Visual, microscopic exam, PCR, culturing, chemical tests Stuck wines are extremely susceptible to spoilage. The sugar offers a substrate for a number of microbes, and any efforts at encouraging completion of fermentation, including warming, aerating, and nutrient addition, will also encourage spoilage microbes. To determine whether non-Saccharomyces yeasts helped cause a stuck ferment, take an unstirred sample and then a stirred one. In the settled lees, there may be large numbers of odd-shaped yeasts, culprits that have died after causing, or contributing to causing, the stuck fermentation. Summary of Wine Microbes — How Many are TOO Many? IN FERMENTATION Kloeckera Juice: more than 5 per 40x field During fermentation: more than 10% of yeast population (Saccharomyces should take over) Stringy clumps are not desirable Other vineyard yeast More than 10% of yeast population Schiz. japonicus (8 spores) Any Saccharomyces Should have more than 2 million/ml at inoculation; more than 100+ million/ml during ferment Viability: should be 50% at rehydration; more than 90% at start of ferment; more than 25%+ near end of ferment Dekkera/Brettanomyces Any (determine by culturing or PCR) Surface film yeast 1 per 40x field Oenococcus At least 1 million/ml if MLF desired Any observed under microscope if MLF not desired Pediococcus Any observed under microscope Lactobacillus 2 per 40x field if population increasing Acetobacter Enough to see under microscope IN ML STARTERS Saccharomyces Dekkera/Brettanomyces Surface film yeast Pediococcus Lactobacillus Acetobacter Should be fermenting with selected, ML-friendly yeast to acclimate bacteria to alcohol Any (determine by culture or PCR) Any observed under microscope Any observed under microscope 2% to 5% if population is rising and starter is for wine with residual sugar, 10% to 20% if starter is for dry wine Any observed under microscope (scan very thoroughly —they may all be in a large clump, not scattered, or in little clumps that are hard to recognize); test with PCR if not sure Lactic acid bacteria Stuck and sluggish wines are often attacked by Lactobacilli (as described above). Any CO2 production in a stuck or sluggish wine should be viewed with suspicion, for it may be caused by Lactobacilli (or Brettanomyces) rather than Saccharomyces resuming fermentation. Monitor stuck wines every day or two under the microscope while reinoculating with fresh yeast. In wines above 3.6 pH, it may be advisable to reduce pH or add lysozyme prophylactically, to reduce the chance of Lactobacillus spoilage. Brettanomyces/Dekkera Fortunately, very few musts become contaminated with Brettanomyces, and anyway, they tend to grow slowly compared to Saccharomyces. However, stuck wines may become infected, especially if they are moved to wood to complete the fermentation. To detect Brettanomyces as soon as possible, culture any stuck red wine once per week, or check periodically by PCR. Production of 4-ethyl-phenol/4-ethylguaiacol (4-EP/ 4-EG) lags behind cell growth by up to one month. This is not the best way to discover a new "Brett" infection in a stuck wine. Certainly, if apiculate yeasts are seen microscopically in a stuck wine, it should be tested for Brettanomyces immediately, but by that time the population may be already quite high. Film on surface Both Acetobacter and surface film yeasts (mainly Candida and Pichia) enjoy conditions that prevail in a stuck wine during reinoculation: warm, low SO2 , not topped. Any film should be examined microscopically. To prevent film, the container should be brought as full as possible, and CO 2 or other inert gas used liberally. Acetobacter can also be discouraged by lowering pH, but yeasts are not as sensitive to low pH as are bacteria. Dry wines undergoing extended maceration are also at risk from Acetobacter spoilage, because there is not enough CO2 produced to prevent their growth. Such wines must be gassed regularly with CO2. ML FERMENTATION Microbes to watch out for: Acetobacter, Lactobacillus, Pediococcus, Brettanomyces, Oenococcus, surface film yeasts Danger signals: VA rise above 0.15 g/L (0.015 g/100ml); the amount produced by Oenococcus from citric acid in stuck wine, film on surface, off-odors or flavors pr actica l win ery & vin eya r d JANUARY 20 14 63