Yeast inoculation

In cold pressing pulp for white wines, present practices vary considerably within the industry. Some processors using continuous presses have found it an advantage to treat pulp with pectolytic enzymes prior to pressing. However, with the Willmes press, cold pulp to which cellulose fibers have been added press with no difficulty, and juice yields have been considered satisfactory. A general practice has been to add pectolytic enzymes to white must before yeast inoculation as an aid to rapid clarification of the new wine. 

Indeed, after a maturation period of 18 months, no significant differences were seen between the wines obtained without the yeast inoculums, either if they were aged in vinsantaia or at a constant temperature of 18 °C, except for the honey character and the color intensity. Similarly, also inside the cluster of wines obtained with both the yeast inoculum and the addition of madre there were no differences found in the perception of individual sensory attributes. However, the wines from the yeast-inoculated fermentation with the addition of madre were perceived to be more acidic, astringent, bitter, and viscous than the non-inoculated wines when they were aged in the cellar at constant temperature (18 °C). In contrast, there were no significant differences among the wines aged under the traditional conditions (vinsantaia). 

Dumont, A., Dulau, L. (1997) The role of yeasts in the formation of wine flavours. In M. AUen, P. Leske, G. Baldwin (Eds.), Advances in juice clarification and yeast inoculation proceedings of a seminar 15 August 1996 Melbourne, Victoria (pp. 14—16). Adelaide S.A Australian Society of Viticulture and Oenology. 

Figure 2. An example of zone clearing found in the yeast inoculated sample— polyurethane from PCL(MW 1250) inoculated with Cr. laurentii on a nitrogen-...

Bacteria were inoculated two days before yeast inoculation. 

Each QP program must include descriptions (criteria) at each step for acceptable fruit quality (sugar concentrations, titratable acidity, microbial contamination, etc.), SOg additions (when and how much), press times and pressures, must clarification procedures, yeast inoculation rates, concen-... 

Lee, S.-J., D. Rathbone, S. Asimont, R. Adden, and S.E. Ebeler. 2004. Dynamic changes in ester formation during Ghardonnay juice fermentations with different yeast inoculation and initial Brix conditions. Am. J. Enol. Vitic. 55 346-354. 

Some vine treatment spray residues (e.g. Folpel) are well known to inhibit fermentation. Sulfur-and chloride-based compounds are the most harmful to yeasts. Inoculation with fresh yeast once the inhibiting residne has broken down is generally snfficient to reactivate fermentation in the must (see Hatzidimitriou et al., 1997). However, certain difficult final stages of fermentation can be attribnted to the presence of these residues. The minimum time between the last application of a product and the harvest date indicated by the man-ufactnrer is not always sufficient. 

The fermentation speed, which depends on must composition (nitrogen-based substances) and yeast inoculation conditions. Operations such as aeration, chaptalization and inoculation will increase the fermentation speed, limit the dissipation of calories and increase the maximum temperature. Reciprocally, not crushing the red harvest in carbonic maceration (Section 12.9.1) will slow fermentation kinetics and lower the maximum temperature. 

During juice settling, certain conditions useful for sedimentation (such as low temperature and sulfiting) can promote the development of certain strains resistant to these conditions. Of course, this growth must not become a fermentation otherwise, it would put the sediments back in suspension. Nevertheless, these strains can develop preferentially during fermentation even after an active yeast inoculation (Fleet, 1992). 

Sulfur dioxide acts more on wine bacteria than on yeasts. Lower concentrations are conseqnently sufficient for hindering their growth or suppressing their activity. No systematic studies have been carried out on this subject but this fact is weU known and is often demonstrated in practice. For example, in the case of a red wine still containing sugar (a site for simultaneous alcoholic and lactic fermentation), a moderated sulfiting (3-5 g/hl) can initially block the two fermentations. Afterwards, a pnre alcoholic refermentation can take place withont the absolute necessity of an yeast inoculation. 

A cool year or cool climate is characterized by a late and often insufficient maturity. Grape acidity is elevated and the musts are thus relatively protected against bacterial attack. However, there is a risk of botrytis attacks and the formation of oxidasic casse, since cool climates often correspond to rainy climates. In addition, grape crops arriving at the winery are often characterized by relatively low temperatures in cool years. As a result, the initiation of fermentation can be difficult, even more so when the grapes are washed by rain the natural yeast inoculation can be insufficient. 

Ferr6 (1958) observed in Burgundy region vineyards that fermentation was activated in 12 hours at 25°C, in 24 hours at 17-18°C and in 5-6 days at 15°C it was nearly impossible at 10°C. These numbers are of course approximate and depend on many other factors, in particular the yeast inoculation concentration. Tanks should not be left at insufficient temperatures. The resulting fermentations are often slow and incomplete, with a risk of mold development beforehand. Tanks are also immobilized for prolonged periods, which can create problems in vineyards that use each tank several times during the harvest. 

The must should therefore be warmed as quickly as possible to 20°C. If the fermentation does not begin shortly after warming, the temperature rapidly drops down to its initial value. A simultaneous yeast inoculation is required to avoid this problem it also accelerates the fermentation and thus provokes a more considerable temperature increase. If the temperature becomes too elevated, cooling may be required after these operations which accelerate the fermentation. Aeration also remains useful, as long as the harvest is not susceptible to oxidasic casse. 

Fermentation rates have been observed to vary under apparently identical conditions (temperature, sugar content, amount of yeast inoculated, etc.). Sluggish fermentations may be completed successfully, but they are always a cause for concern. Besides specific factors in the must, one explanation is that several yeast sfiains are involved and fermentation kinetics may be affected by antagonism between them (Killer effect. Sections 1.7 and 3.8.1). 

Fermentation. Today (ca 1997) it is almost universal to inoculate the must with a selected yeast strain. Yeasts are chosen for conducting predictable, prompt, and complete fermentations under the conditions appHcable for the particular wine. It is tme, at least in most wineries, that grapes will ferment with the yeasts naturally present. At one time it was argued that part of the special regional character of wines was the result of the local yeasts. 

The production of soda crackers is also based on a mixed fermentation. Doughs for cracker production are inoculated with very smaH amounts of bakers yeast. During the first 3—5 h of the 18-h fermentation, yeast activity predominates thereafter bacterial fermentation causes a rapid decrease in pH through formation of lactic acid. 

Wine. The earliest known wines were made in Iran about 5400—5000 BC (25). The species of grape used is unknown and may have been either the wild grape Fitis viniferus sylvestris or a cultivated precursor of the modem wine grape V. viniferus viniferus. The source of the yeast used, and the procedures used are completely unknown. In modem times, grapes (about 21—23% sugar) are pressed the liquid must is either separated and allowed to settle for 1—2 days (for white wines) before inoculation with yeast, or the whole mass is dkectly inoculated with yeast (for red wines). In either case, while the initial fermentation takes place, the carbon dioxide formed by fermentation excludes ak and prevents oxidation. White wines are transferred to a second fermentor (racked) near the end of fermentation and kept isolated from the ak while solids, including yeast, settle out, a process that requkes about six... 

Spontaneous fermentations are used for wine production in Erance, some other European countries and in South America. In recent years, smaller California wineries have begun experimentation with spontaneous fermentations as well. They generally start more slowly than fermentations inoculated with commercial dried yeast, are more difficult to control, and may suffer from growth of undesirable contaminants. However, it is claimed that the resulting wines possess better organoleptic properties, particularly more complex flavor and aroma. 

The function of Jisper Uis fermentation appears to be primarily the breakdown of protein and polysaccharides by secreted proteases and amylases. Replacement oiPispergillis by chemical or enzymatic hydrolysis has no major impact on the organoleptic properties of the sauce. Likewise, inoculation with a pure culture of Ixictobacillus delbrueckii to carry out the acetic acid fermentation produces a normal product. The S. rouxii and Toru/opsis yeasts, however, are specifically required for proper flavor development. 

The yeast must be so finely dispersed throughout the wort that a quick yeast growth is assured, which leaves no possibiUty for other microorganisms, if any, to develop. The inoculation of yeast occurs through injection directly into the wort pipe. To be used in the next batch of wort, the yeast that is harvested after the end of fermentation must be protected against contamination. 

Full-bodied mms are akowed to ferment from 12 to 20 days, often relying on natural or wild fermentation in which the mash is inoculated by the yeast present in the air and starting materials. These mms are twice-distiked in pot stiks to 140—160° proof. Full-bodied mms are often aged from five to seven years in oakbarrels. Caramel color can also be added to give them a darker color. They are produced in Jamaica, Barbados, Martinique, Trinidad, and Guyana. 

Selected yeast strains of Saccharomjees cerevisiae are used to inoculate the mash. Two to four percent (v/v) is a minimum for bourbon, which represents over four million cells per milliliter of mash. During fermentation the cells grow in number via budding and the final counts are increased a minimum of 100-fold. 

For this purpose a fermenter made of stainless steel having a 50 liter capacity is charged with 30 liters of a nutrient solution of 0.1% yeast extract, 0.5% cornsteep and 0.2% glucose, heated for one-half hour at 120°C for sterilization purposes, and after cooling, inoculated with a bacterial suspension of Bacillus lentus MS 2B4. 

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