Temperature control during fermentation

Proper, timely addition of SO 2 Temperature control during fermentation Pure yeast cultures... 

Fermentation generates heat, and red wines must have some type of temperature control during their fermentation. They must not be allowed to get too hot or to become too cold. Ough and Amerine (18) recommended temperatures of 18°-29° C and found that cap temperatures can exceed liquid temperatures by over 6° C. In large stainless steel fermentors, the author has noted cap-liquid temperature differences of 11°. 

The pH of the media must be monitored and, in many cases, held constant. Temperatures must be carefully controlled during fermentation to maximize yields. The nature of the media, such as carbon and nitrogen sources, directly determines the quality of the odor released and the range of secondary metabolites produced. Optimization of the production of volatiles must also take into account the physiological state of the microorganisms. 

Why does the temperature need to be carefully controlled during fermentation ... 

A typical bourbon fermentation continues for 72 hours at a fermentation temperature within the 31—35°C range. Many fermentation vessels are equipped with agitation and/or cooling coils that facHitate temperature control. Significant increases in yeast numbers occur during the first 30 hours of fermentation. Over 75% of the carbohydrate is consumed and converted to ethanol. Within 48 hours, 95% or more of the ethanol production is complete. 

Fermentation Curves. Fermentation curves are an index of the general well being of the fermentation processes taking place in the fermentation room. Abnormal yeast populations or improper temperature control often can be seen first in the plotted data of sugar content vs. time during fermentation. 

In California, temperatures of the secondary fermentation range from 10° to over 25° C in different wineries. Cool, slow fermentations are preferred by some, and warm, quick fermentations by other wineries. Bottle-fermented processors commonly chill the cuvee to 10°-15° C before bottling. One cellar is temperature controlled to 10°-13°C and another at 18° C. Other cellars are naturally cool summer and winter. Unfortunately, a few cellars are not temperature-controlled or well-insulated, and the temperaures can vary from 10° C in winter to as high as 22° C in summer. Bulk wine processors may or may not chill the cuvee before fermenting in insulated tanks. Most do not chill during fermentation and report temperaure increases of 3°-8° C (theoretical is about 3° C). 

Brandis JW, Ditullio DF, Lee JF, Armiger WB (1989) Process controlled temperature induction during batch fermentations for recombinant DNA products. In Computer applications in fermentation technology. Elsevier, London, p 235... 

Mannitol. Whereas mannitic fermentations are seldom a problem where sulfur dioxide, pure yeasts, and temperature control are employed, Martucci (1941) has reported them in Argentina. He recommended control of the must acidity, since a high pH also favored such spoilage. A complicated polaiimetric procedure for mannitol (a sugar alcohol) in wines was presented by Salani (1937). Formation of mannite during dialysis of musts at low temperatures (8° to 10° C. (46.4° to 50° F.)) in the presence of chloroform was reported by Barbera (1933b) (possibly owing to enzyme action). 

Because the volume of the fermentation mixture is only about 20 mL, it is necessary to use an external heat source to maintain a temperature of 30-35°C. An incubator will provide the necessary temperature control. One can make a simple incubator by placing a cardboard box over a light bulb that is turned on during the fermentation. Be sure that the box does not touch the light bulb and has adequate clearance. Use aluminum foil to seal any openings and to help reflect the heat inward. 

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