Fermentation temperatures

Fermentation temperature plays an important role in establishing numerical superiority between Saccharomyces and non-Saccharomyces species. In red wine fermentations (68-86°F/20-30°C), Saccharomyces represents 

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Genetic manipulation or cloning offers many possibiUties and perhaps there will be yeast strains especially designed for special beers, ie, types, which are usehil because of low diacetyl formation, high—low ester formation, and insensitivity to pressure or high fermentation temperatures or extracellular enzymatic abiUties (P-glucanases). 

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. 

The converted mash is pumped to a clean sterilised fermentor and the yeast inoculum is added. The set temperature range for whiskey fermentation of 72 hours is usually 17—21°C. At the beginning, the mash converted composition is approximately 80% sugars, mainly maltose and some (<1%) dextrose (primary conversion). The pH is adjusted to reduce initial bacterial growth. Grain neutral spidts are usually set at 27—29°C to expedite fermentation. Temperatures above 35°C inhibit yeast reproduction and promote rapid bacterial growth. Above 40°C actual yeast kill occurs. 

The production of benzylpenicillin is very sensitive to temperature. A lot of metabolic heat is generated and the fermentation temperature has to be reduced by controlled cooling. This heat transfer is achieved by circulating chilled water through banks of pipes inside the vessel (which also serve as baffles) or through external limpet coils on the jacket of the vessel. These coils consist of continuous lengths of pipe welded in a shallow spiral round the vessel. This cooling water system is also used to cool batched medium sterilized in the vessel prior to its inoculation. 

Maintenance of fermentation temperature at 15°C increases theaflavin levels whereas higher temperatures vary for thearubigen formation. Teas fermented at 15°C bring higher prices than those manufactured at 25 °C or... 

Cloughley, J. B., The effect of fermentation temperature on the quality parameters and price evaluation of Central African black teas. J. Sci. Food Agri., 31 911, 1980. 

Irradiation shortens the composting period, because it is not necessary to keep an elevated fermentation temperature to reduce the pathogens in the sludge. 

Suppose we are interested in investigating the effect of fermentation temperature on the percent alcohol response of the wine-making system shown in Figure 1.6. We will assume that ambient pressure has very little effect on the system and that the small variations in response caused by this uncontrolled factor can be included in the residuals. Further, we can use the same type and quantity of yeast in all of our experiments so there will be no (or very little) variation in our results caused by the factor yeast . 

A summary of the factors which are known to influence ethanol production from glucose in a gas-solid fluidized bed fermenter, or which may have an influence based on observations with submerged fermentations, is shown in Figure 6.1. In anaerobic beds, the key factors are the fermentation temperature and ethanol inhibition, both of which have a dramatic effect on the specific rafe of ethanol production. Bed dehydration and its influence on yeast pellet moisture content is also important, since a failure of fermentation may occur if the pellets become too dry (Bauer, 1986). 

At the start of the batch fermentor operation, the broth must be heated to the fermentation temperature, which is usually in the range of 30-37 °C, by passing steam or warm water through the coil or the outer jacket. 

To show correlation between occurrence of malo-lactic fermentation and bacterial inoculation, and to show consistency of results among the control lots and inoculated lots, it is imperative that the division of lots be made before alcoholic fermentation. For red wines, great care must be taken to obtain equitable distribution of the crushed grapes in each of the lots. The inconsistency in the results mentioned above may have been caused by variation in amounts of grape skins during the alcoholic fermentation with the accompanying effect on fermentation temperature, sulfur dioxide concentration,. pH after pressing, and concentration of nutrients (55, 56). 

Let us carry out a so-called screening experiment in which we attempt to discover if the fermentation temperature (factor x ) has a significant effect on the response (% alcohol content). We will choose two levels of temperature, 23°C and 27°C. This is the minimal number of factor levels required to fit the two-parameter model... 

The pH was maintained at 5.0 by the addition of 2 M NaOH (Micro DCU-300 B. Braun Biotech). The fermentation temperature was 30°C and the stirrer speed was 500 rpm (MCU-200 B. Braun Biotech). Cell mass was produced in an initial batch phase using a glucose concentration of 64 g/L. The concentrations of mineral salts, trace metals, vitamins, and Ergosterol/ Tween-80 were the same as in the fed-batch experiments. When the glucose in the batch medium was completely consumed, 1.9 L of dilute-acid hydrolysate was pumped into the reactor at maximum pump speed, by using a peristaltic pump (Ul-M Alitea AB). The ratio between batch volume and the final volume (i.e., after all the hydrolysate had been added) was similar to the ratio in the PDU fed-batch experiments, approx 1 4. The reactor medium was sparged with nitrogen (600 mL/min). The C02 content in the exhaust gas was measured with a gas analyzer (TanDem Adaptive Biosystems, Luton, UK). 

All chemicals were laboratory grade and dissolved in distilled water. The medium was sterilized by autoclaving, and sorption experiments were performed in sealed 150-mL serum bottles. Subsequent tests for in situ use may need to be performed at mesophilic fermentation temperatures. In a similar manner, the sorbents were also tested for their capacity for the substrate of the possible fermentation, glucose, at a concentration of about 5 g/L. Frequently the glucose was included in the fermentation medium for competitive sorption. 

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