Influence Of Fermentation Temperature Research Articles

Influence of Fermentation Temperature on Composition and Sensory Properties of Semillon and Shiraz Wines

Crushed Semillon grapes were pressed after 24 hr pomace contact and fermented at one of four temperatures (15, 20, 25, or 30°C) to assess the effect on the chemical composition and sensory properties of the wines. An additional treatment (15°C fermentation without prior pomace contact) was included to assess the impact of pomace contact. Shiraz grapes were fermented according to one of three temperature regimes (15°C; 20°C for 3 days followed by 30°C; 30°C for 3 days followed by 20°C), with and without a prefermentation cold soak. An additional treatment involved a cold soak, 20°C fermentation temperature for 3 days followed by 30°C, plus a 3-day postfermentation extended maceration. Increasing fermentation temperature in Semillon tended to increase titratable acidity (TA) and absorbance (A₄₂₀) slightly. The 20 and 30°C temperatures resulted in the highest ethanol content. Pomace contact reduced wine TA and increased pH and A₄₂₀. Within the two 15°C treatments, tasters found pomace contact wines had less earthy aroma and herbaceous flavor. Among the pomace contact treatments, 15°C fermentations resulted in less yellow color and herbaceous aroma, and fruitier aroma than 30°C fermentations. Increasing fermentation temperature, use of cold soak, and extended maceration tended to reduce Shiraz wine TA and increased pH and anthocyanins. Use of cold soak increased color (15°C only) and black currant flavor, reduced herbaceous flavor, but reduced black currant aroma. Extended maceration enhanced wine color and body but increased herbaceous aroma. Increasing fermentation temperature from 15 to 30°C increased wine color, reduced herbaceous flavor, increased black currant flavor, but increased perceived acidity. These results suggest that Semillon wines should be produced through the use of prefermentation pomace contact and cool fermentation temperatures, whereas Shiraz wines would benefit from higher fermentation temperatures, use of cold soak, and extended postfermentation maceration.

By-products formed during direct conversion of sugar beets to ethanol byZymomonas mobilis in conventional submerged and solid-state fermentations

The nature and amounts of by-products formed during conversion of sugar beets to ethanol byZ.mobilis in Conventional Submerged Fermentation (CSF) and Solid-State Fermentation (SSF) were investigated. It was found that the bacterium produced fewer by-products in SSF than CSF, and that by-products profile was different. The influence of fermentation temperature on synthesis of by-products in SSF was also studied. High fermentation temperature favoured sorbitol synthesis and low fermentation temperature the synthesis of levan. The best results were obtained at 35°C. An ethanol yield of up to 95% of the theoretical value with final ethanol concentration of 142 g/L were obtained.