Proceedings Volume 2010 (format .pdf) - SimpBTH

duration of pre-fermentative phase, shows that in all cases when it has been usedselected yeasts, the alcoholic fermentation started more rapidly due to higherdensity of initial population. The differences are more important in whitewinemaking, where the higher doses of sulphur dioxide and the must clarificationdecrease significantly the initial level of indigenous yeasts population. While thewhite must, regardless of variety, vineyard or wine year, from debourbage to thebeginning of decrease of must density, takes between 30 to 72 hours atfermentation with indigenous yeasts, by addition of selected yeasts, the must startfermenting in less than 30 hours. Most of the times, the start of fermentation occursin less than 24 hours. This tendency has been noticed also on red winemakingmentioning that the differences are little bit smaller due to maintaining of yeastsfrom indigenous micro flora in contact with the must.Table 1 The influence of different types of yeasts on the ongoing alcoholic fermentationType ofyeastsWines Duration of prefermentativephase,hoursDuration offermentation,daysFermentationefficiency g/% vol.alcoholIndigenous White 30 – 72 10 – 18 16.8 – 17.4yeasts Red 18 – 48 8 – 14 17.2 – 17.8Selected White 18 – 30 8 – 12 16.4 – 17.1yeasts Red 12 – 24 6 – 9 16.7 – 17.2The second aspect analyzed is the duration of alcoholic fermentation,depending on type of wines (white or red) and the winemaking conditions,especially the temperature control. In the case of selected yeasts, the duration offermentation is 2-3 up to 8-10 days shorter, a very important aspect from economicand oenological point of view. The start and faster ongoing of alcoholicfermentation, eliminating the slowly and stop of fermentation represent one of themajor advantage and the main argument in favor of using selected yeasts inwinemaking.Another aspect analyzed related to the yeasts fermentative capacity is thefermentation efficiency. The data from Table 1 show that the selected yeastsconsume less sugar to produce 1% volume of alcohol, whatever the type of wine.So, in the white must, the selected yeasts consume between 16.4 – 17.1g of sugarwhile the indigenous yeasts consume between 16.8 – 17.4g of sugar to produce 1%alcohol. In red must, the consumption is little different and here the selected yeastshave better fermentation efficiency.The superior fermentative capacity of selected yeasts is reflected inchemical composition of wine, as it can be seen from Table 2 where is representeda synthesis of results regarding the modification of main composition parameters offermented wines with selected yeasts comparing to indigenous yeasts. From several136