Sorbitol and alcohol determination using an ebulliometre

[wayne]

Hi all

I recently fermented a single variety perry. The fruit came from a very old tree. After fermentation had completed ( Laforte X16 ), I tested that no residual fermentable sugar remained. There was none.

The hydrometer read 1.008. This indicated to me a reasonable level of sorbitol remains. My question is: my ebulliometre returned a result of 6.2% alc.  Does the sorbitol in the perry affect the ebulliometre reading in the same way that fermentable residual sugar does ?

Thanks

[winters...@gmail.com]

Its my understanding that the ebulliometer determines alcohol content based on the boiling point of the existing alcohol in your sample, so I would not expect other residual sugars or sorbitol to affect it.  Having said that, I'm no expert though, and not much of a "scientist" compared to others in this Group.

G

[Claude Jolicoeur]

Le vendredi 30 mars 2018 11:41:05 UTC-4, winters...@gmail.com a écrit :

Its my understanding that the ebulliometer determines alcohol content based on the boiling point of the existing alcohol in your sample, so I would not expect other residual sugars or sorbitol to affect it. 

It is well documented that high residual sugar content does in fact affect boiling point and ebulliometer result.

However, I do not know to what extent. I have seen references to correction factors in function of sugar, but never found them.
It is well known that for ice cider with some 130 g/L residual sugar, the ebulliometer doesn't give a good result.
As of sorbitol, and for the relatively low level mentioned, I don't know, but I wouldn't think the error would be very important.
Claude

[Andrew Lea]

There are discussions of the ebulliometer  sugar correction in sweet wine  in many wine analysis textbooks and eg here http://seniorchem.com/2.%20Alcohol-Content-by-Ebulliometry.pdf

Since the elevation of boiling point is a colligative property, I would expect one mole of sorbitol to give the same BP elevation as one mole of glucose or one mole of fructose. 

 I think one of the reasons for poor accuracy of this technique in sweet wines and ciders might be that you do not know the extent of hydrolysis from one mole of sucrose into potentially two moles of glucose plus fructose, and anything in between. 

Andrew 

Wittenham Hill Cider Portal
www.cider.org.uk

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[Claude Jolicoeur]

For what it is worth, the correction suggested in that paper is in function of the Baumé degrees. We know 7.2 points of density is equivalent to one degree Beaumé. So, for example, a wine or cider with a final SG of 1.010 would be at 1.4 degree Beaumé, and the correction in that case would be of 2% on the alcohol strength - i.e. if the ebulliometer result is 5% ABV, the true strength would be 4.9%. Quite a small correction.
Claude

[winters...@gmail.com]

Many thanks, guys!