Sugars in Winemaking

[Don Giovanni]

Sugars in Winemaking

So the unfermentable sugars are in fact fermentable , but due to atrophied 5 Carbon system in S. C. yeast...so some wine can have unfermentable sugars, but this is rare due to the yeast defect...at one time it was thought that the 5 carbon unit sugars could only be fermented with frankin yeast...today I see this is not the case...still most wines will have unfermentable sugars fermented no lower than .03% RS

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look for unfermentable sugars in this web site...

from Arthur Black of National Wine & Spirits in Indianapolis:

“Can anyone tell me why yeasts can only metabolize the six-carbon sugars glucose and fructose, while five-carbon sugars like ribose and xylose are unfermentable? I

using a painstakingly patient technique to show that the atrophied 5-carbon system in S. cerevisiaecan be made healthy again by a mixture of natural selection and breeding techniques.

“In essence the whole story boils down to what the yeast really needs to survive. Metabolic pathways that allow use of 5-carbon sugars when the yeast rarely has a need to use them are wasteful whereas the production of ethanol to ‘clean’ the environment is a much higher priority.  It may be when the yeast is dominant in an environment then its slower metabolic rate of the 5-carbon sugars is not an issue.  Ability to use sucrose/glucose is much more advantageous to wine yeast.

Attfield, P. V. & Bell, P. J. L. (2006). Use of population genetics to derive nonrecombinant Saccharomyces cerevisiae strains that grow using xylose as a sole carbon source. FEMS Yeast Research 6, 862-868.

Verstrepen, K. J., Iserentant, D., Malcorps, P., Derdelinckx, G., Van Dijck, P., Winderickx, J., Pretorius, I. S., Thevelein, J. M. & Delvaux, F. R. (2004). Glucose and sucrose: hazardous fast-food for industrial yeast? Trends Biotechnol 22, 531-537.”

As for alc conversions yeast genetic health will make the numbers differ each year...thus we go by as low as .55 to .61 or so I use .585 and do just fine and hit the alc mark most of the times...Scott Lab yeast questions and answers...

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