Temperature, winemaking

Mallouchos A., Loukatos R, Bekatorou A., Koutinas A.A. and Komaitis M. Ambient and low temperature winemaking by immobilized cells on brewer s spent grains Effect on volatile composition. Food Chemistry 104 (3) (2007) 918-927. 

Beltran, G., Novo, M., Leberre, V., Sokol, S., Labourdette, D., Guillamon, J. M., et al. (2006). Integration of transcriptomic and metabohc analysis for understanding the global responses of low-temperature winemaking fermentations. FEMS Yeast Research, 6, 1167-1183. 

To prevent the formation of wine crystals during the bottling process, winemakers use a method known as cold stabilization. By lowering the temperature of the wine to 19-23°F for several days or weeks, the solubility of tartrate crystals is lowered, forcing the crystals to sediment. The resulting wine is then filtered off the tartrate deposit. The temperature dependence of the solubility of potassium bitartrate is readily apparent in the following comparison while 162 ml of water at room temperature dissolves 1 g of the salt, only 16 ml of water at 100°C are needed to solubilize the same amount of saltJ l Recent developments employ a technique known as electrodialysis to remove tartrate, bitartrate, and potassium ions from newly fermented wine at the winery before potassium bitartrate crystals form. 

The growth of malo-lactic bacteria in wines is favored by moderate temperatures, low acidity, very low levels of S02, and the presence of small amounts of sugar undergoing fermentation by yeast. It is frequently possible to inoculate a wine with a pure culture of a desirable strain of bacteria and obtain the malo-lactic fermentation under controlled conditions. The pure-culture multiplication of the selected strain of bacteria is difficult, however. It is also difficult to control the time of the malo-lactic fermentation—sometimes it occurs when not wanted, and at other times will not go when very much desired. For the home winemaker it is probably most satisfactory to accept the malo-lactic fermentation if it occurs immediately following the alcoholic fermentation. The wines should then be siphoned away from deposits, stored in completely filled containers at cool temperatures, and have added to them about 50 ppm S02. If the malo-lactic fermentation does not take place spontaneously and the wine is reasonably tart, the above described regime of preservation will likely prevent its occurrence. When the malo-lactic transformation takes place in wines in bottles, the results are nearly always bad. The wine becomes slightly carbonated, and the spoiled sauerkraut flavors are emphasized. 

FIGURE 1.1 Scheme of carbonic maceration winemaking. AM, anaerobic metabolism of grape berries YAF, yeast alcoholic fermentation M, maceration qd = pair temperature (q°C) action duration (days). (Figure from CEnologie—fondements scientifi-ques et techniques. Flanzy et al. collection Sciences Techniques Agroalimentaires. Technique Documentation, 1998, p. 780. Reproduced with the permission of the Editor.)... 

Erten, H. (2002). Relations between elevated temperatures and fermentation behaviour of Kloeckera apiculata and Saccharomyces cerevisiae associated with winemaking in mixed cultures. World J. Microbiol. Biotechnol. 18, 373-378. 

Today, Madeira is noted for its unique winemaking process, which involves heating the wine up to temperatures as high as 50 °C for an extended period and deliberately exposing the wine to some degree of oxidation. Because of this unique process, Madeira is a very robust wine that can be long-lived, even after being opened (Stevenson, 2005). 

In order to evaluate the best temperature and time of baking process, Silva et al. (2008) used an expert panel to analyze seven descriptors, including dried fruit, nutty, baked, oak, mushroom, and brown sugar. The optimal temperature and time of baking process respecting the specificity of Madeira winemaking are considered 45 °C for 4 months. On the basis of aroma extract dilution analysis (AEDA), several Maillard byproducts, such as Sotolon, 2-furfural, 5-methyl-2-furfural, 5-ethoxy-methyl-2-furfural, methional, and phenylacetaldehyde, were identified in both Malvasia and Sercial wines under study which may explain the baked, brown sugar, and nutty odor descriptors. 

The environmental condition under which fermentation occurs is very different from those of traditional autumnal winemaking, and imposes clear difficulties. The temperature of the must is often about 5 °C, or lower and its high sugar content jointly impede the onset and conduct of fermentation. 

Total phenols extracted into red wines by skins and seeds usually increase with an increase in contact time, temperature, ethanol, SO2, and maceration. These are the factors at the winemaker s disposal that have a large effect upon the style of wine he wishes to produce. 

The fluidity of the plasmatic membrane is considerably affected by temperature (Rodriguez et al. 2007) and ethanol concentration (Jones and Greenfield 1987). Therefore, during alcoholic fervaeniaiionSaccharomyces cerevisiae must adapt the fluidity of the membrane to the changing environmental conditions. It should be emphasized that the temperature of fermentation and aeration depend on the type of winemaking. Usually, white wines are made at low temperatures (14-18 °C) and without aeration to conserve aromas whereas red wines are fermented at relatively high temperatures (28-30 °C) and are aerated in order to enhance colour extraction. 

In white winemaking, Saccharomyces cerevisiae must develop at low temperature, which reduces membrane fluidity. To maintain adequate fluidity in their membranes, yeasts increase the proportion of UFA in the phospholipids (Thurston et al. 1981 Torrija et al. 2003). Phospholipids with unsaturated fatty acids have a lower melting point and more flexibility than phospholipids with saturated acyl chains (Rodriguez et al. 2007). Such adaptation involves inducing the fatty acid desaturase OLEl which incorporate unsaturated bonds at defined positions in fatty acids (Nakagawa et al. 2002). 

Presence of medium chain fatty acids The presence of MCFA can decrease yeast viability and even stop alcoholic fermentation. This problem is more prevalent in white winemaking because fermentation is usually carried out at low temperatures and without any aeration. Yeast hulls have been very useful for avoiding this problem. Yeast hulls adsorb MCFA from the media and provide sterols and UFA to the yeasts. Yeast hulls can be used as preventives (20 g/hl) or as curatives (40-50 g/hl) of stuck and sluggish fermentations. 

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