Film yeasts

The visual manifestation of oxidative yeast activity is the formation of a film, sometimes referred to as mycoderma. The film results from repeated budding of mother and daughter cells that, rather than separating, remain attached, forming chains that branch and rebranch to eventually cover the surface of the wine (Section 1.2.2.4). Initially, the yeasts can appear as floating flowers. If allowed to continue, growth may rapidly develop into 

Use of lower cellar temperatures ( 15°C/60°F) can slow the growth of film yeasts because the alcohol content and temperature interactively inhibit growth. As support, Dittrich (1977) reported no growth of filmforming yeasts in wines of 10% to 12% alcohol when stored at 8 C/47 F to 12°C/54°F, whereas growth was observed in other wines up to 14% alcohol at warmer temperatures. 

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With a special (usually oxidized or heated) odor, the result of treatment or aging ( d) Without film yeast involvement... 

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The Spanish sherry type of film yeasts tolerate high alcohol concentrations (up to 16 percent) and cause compositional and taste changes which are considered to be serious defects in nearly all wines except Spanish-type flor sherries. The most obvious compositional changes in... 

Acetaldehyde. In routine winery operation acetaldehyde is seldom measured. However, in the production of sherry, either by the film yeast or submerged culture processes, regular acetaldehyde determination is necessary. 

Full Tanks. A sound tank that is kept adsolutely full cannot have any significant amount of spoilage from film yeast, aerobic bacteria, or the direct effects of oxygen reaction. 

Film yeast wines do not benefit from bottle aging. Indeed, they are at their best when drunk from the last stage of the solera and deteriorate in flavor with time in bottles. 

The development of an oxidized odor in white table wines was common. However, those who burnt sulfur freely in their casks (to produce SO2) had no trouble. Film yeast growth on dry white wines was also a problem, indicating poor cellar practice. The baking of wine to produce sherry was practiced already in California in 1884—in sherry houses. ... 

Recently Webb (16) explained the aromas of film sherries as by-products of an incomplete metabolic sequence where ethanol is being metabolized by film yeasts to carbon dioxide and water. Webb also refers to Pasteur s Etudes sur le Vin, published in 1866, as the basis of the specialization of zymology, which recognizes different types of film formers that yield the wines of the Jerez district of Spain, Vinsjaunes of the Jura region of France, and the flor wines of Australia, South Africa, the Soviet Union, and California. 

Wurz, R. E. M., Kepner, R. E., Webb, A. D. (1988) The biosynthesis of certain gamma-lactones from glutamic acid by film yeast activity on the surface of Flor Sherry. American Journal of... 

Aldehydes also arise as normal by-products of yeast fermentation. Acetaldehyde is the ultimate electron acceptor in the conversion of glucose to ethanol. In this pathway, aldehyde dehydrogenase (ADH) reduces acetaldehyde to ethanol with the corresponding oxidation of NADH. Acetaldehyde levels are therefore dependent on the fermentation conditions, e.g., temperature, O2 levels, pH, SOj levels, and yeast nutrient availability (13, 14). Yeast strain can also affect aldehyde formation and excretion (15-17). For example, film yeasts used in sherry production are selected for their ability to produce very high acetaldehyde levels (18). 

The imperfect genus Candida comprises the largest collection of similarappearing asexual yeasts. Members of the group are familiar to most winemakers in that they play important quantitative and qualitative roles in the community of yeasts collectively called film yeasts. ... 

Hansenula anomala has both fermentative (albeit limited) and oxidative capabilities (growing as a film yeast). When growing fermentatively, Hansenula is capable of producing from 0.2% to 4.5% (vol/vol) alcohol along with potentially large amounts of acetic acid (1-2 g/L) and ethyl acetate (2150 mg/L) and isoamyl acetate (Shimazu and Watanabe, 1981 ... 

In wine, Hansenula exists as part of the film yeast community, where it utilizes ethanol, glycerol, and wine acids in the production of acetic acid and acetaldehyde as well as esters of which ethyl acetate and 3-methylbu-tylacetate may be the most notable (Sponholz and Dittrich, 1974). Acid utilization by H. anomala may be substantial, resulting in measurable decreased titritable acidity and upward pH shifts (Sponholz, 1993). 

Low fermentation temperatures (10-15 0,) reportedly extends the alcohol tolerance range of C. stellata (Gao and Fleet, 1988). However, in aging wine, the interactive effects of alcohol and low (<15°C/60°F) cellar temperature retards growth. This observation is not unique to Candidahul is characteristic of film yeast in general. 

Acetaldehyde is a normal by-product of alcoholic fermentation, but it may increase during aging owing to oxidation of ethyl alcohol or to the activity of film yeasts. It is easily fixed by sulfur dioxide, so that much of that present is bound. ... 

Formation. The experiments of Mestre and Campllonch (1942) support the view that acetaldehyde is an intermediary in the process of alcoholic fermentation. In some cases they report high volatile acidity arising from oxidation of aldehydes, even in the absence of bacteria. Uchimoto (1951) found a positive correlation between temperature of fermentation and amount of acetaldehyde formed. Many investigators have demonstrated a rapid rise in the aldehyde content of wines under a film yeast. Ter-Karapetian (1952) has studied the formation of acetaldehyde in 16 % alcohol wines. Aldehyde formation occurred only when the wine was aerated and yeast cells were present. Fornachon (1963) has... 

The spoilage bacteria of dessert wines isolated by Fomachon (1943) were very sensitive to a pH of below 3.5 this is probably the primary reason why so many European wines are relatively resistant to bacterial spoilage. A decrease of pH during growth of the film yeast in sherry production was reported by Marcilla et al. (1936). The changes in pH during the malo-lactic fermentation are summarized by Schanderl (1950). 

The distribution of yeast species in cellar-aging wine includes Dekkera/ Brettanomyces (Section 11.2.2), film yeasts (Section 11.2.3), Saccharomycodes (Section 11.2.4), and Zygosaccharomyces (Section 11.2.5), all of which can result in serious wine spoilage. 

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