In whisky production, there is very little information regarding the influence of wort insoluble material on the fermentation. Therefore, an investigation into the influence of wort solid material on the fermentation of whisky wort by yeast was undertaken. Initial studies involved assessing the effects of wort solids on a small-scale fermentation system. Fermentation parameters, such as decrease in wort specific gravity (SG) and free-amino nitrogen (FAN) were assessed during fermentations of clarified and cloudy wort. Results showed fermentation of cloudy wort to be faster and more complete. Shaking fermentations of clear wort appeared to negate these effects, allowing fermentation to proceed like that of cloudy wort, but differences in the amount of FAN consumed were apparent. Clarification of wort by centrifugation resulted in altered fermentation parameters compared to addition of wort solids back to clear wort, suggesting a role for the physical nature of the solids. Clarified wort was shown to contain an elevated C02 concentration after 5 and 8 hours fermentation (ca. 5 g/L), but addition of an inert material (diatomaceous earth (DE)) decreased the concentration to levels observed in cloudy wort (ca. 2 gIL). Bentonite, another inert material, did not have the same ability as DE. Environmental Scanning Electron Microscopy revealed that the solids with porous surface topography (wort solids and DE) were more effective as CO2 nucleating agents. Static 1L fermentations of whisky wort were also carried out. A model was devised whereby clear wort was supplemented with DE at a concentration similar to that of solids in cloudy wort. Differences during fermentation were still apparent between cloudy wort and clear wort with DE, which could not be accounted for by elevated C02 concentrations. A series of fermentations were performed where clear wort with DE was supplemented with long chain fatty acids and fermented in conjunction with cloudy wort. There were no apparent effects after addition of hexadecanoic, octadecadienoic and octadecatrienoic acids, but fermentation was enhanced with the addition of the unsaturated fatty acids hexadecenoic acid and octadecenoic acids. Zinc addition enhanced fermentation slightly, but not to the same level as cloudy wort. The effects of differences in mashing technique in a commercial setting were investigated. There was a decrease in the initial concentration of FAN in worts where the first sparge temperature was 90°C, as opposed to 76 °C, and a higher concentration of solids and long-chain fatty acids. These worts fermented more quickly, in terms of consumption of FAN by yeast, during early fermentation. Differences were also observed in the concentration of volatiles (esters and higher alcohols) between worts after 50 hours fermentation. Dielectric measurements taken over a 72 hour, temperature-controlled fermentation period revealed fundamental differences in yeast cell behaviour during fermentation of wort from different distilleries. Worts were also produced in the 2 hL pilot plant at Heriot-Watt University, Edinburgh, to determine the effects of experimental differences in mashing regime on the subsequent wort. Again, fundamental differences were observed during fermentations, which appeared to be linked to differences in the components present in different worts. From these results it was hypothesised that the ability of yeast to consume and utilise a range of compounds in wort would render them more resistant to stress, particularly when more fatty acids were available.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:271661 |
| Date | January 2002 |
| Creators | Orchard, Vivienne |
| Publisher | Queen Mary, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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