1. International Wine Technical Summit, 2017
Harmonizing Expression of Measurement Results in Wine Analysis: Best Practices When Testing and Reporting Sugar in Wine
International Wine Technical Summit, 2017
M. Sarita Cardozo
Chemist
Compliance Laboratory
Scientific Services Division
Alcohol and Tobacco Tax and Trade Bureau
Walnut Creek, CA

2. Summary This paper proposes the following best practices:
Clarify abbreviation ‘RS’ when used.
Express residual sugar as sum of glucose, fructose and sucrose in g/L of wine.
Use test methods specific for wine sugars.
Avoid reporting sugar alcohols, such as glycerol, as a sugar.
Avoid testing for sugars not expected in wine.

3. Background Paper developed in response to:
Dialog among past IWTS participants
Trade problems due to sugar results from different methodologies
Observed results for sugars in the 2015 APEC Wine Regulatory Forum Ring Test

4. 2015 APEC WRF Ring Test Results - Sugars in Red Wine
Method
N (APEC)
APEC Mean (g/L)
APEC (%CV)
N (IWAG)
IWAG Mean (g/L)
IWAG (%CV)
Reducing Sugars 12
4.51 ± 1.39 29 42
4.34 ± 0.8 18
Glucose+Fructose 10
2.24 ± 0.53 24
110
2.3 ± 0.41

5. Why is this a problem?
Some economies have sweetness labeling standards:
- Dry: Max of 4 g/L
- Medium dry: 4 – 12 g/L
- Semi-sweet: 12 – 45 g/L
- Sweet: > 45 g/L
Sugar-free extract calculated from erroneously high sugar results are erroneously low.
Trade has been impacted by these labeling issues.

6. Sugar Composition in Wine
Typical sugar composition:
- glucose + fructose = 95%
- sucrose 3%
- pentoses and other sugars 2%
Not expected:
- maltose
- lactose
Sugar alcohols are not sugars:
- glycerol
For wine: Residual sugar (RS) refers to sum of glucose + fructose + sucrose

7. What is ‘RS’? Reducing Sugar Residual Sugar Reducing Substance
Sugar with an aldehyde or keto group
Fermentable sugars
Any substance than can reduce copper ions in solution
Glucose & fructose
Glucose &
fructose
Pentoses (non-fermentable)
Sucrose
Oligosaccharides
Tannins & polyphenols

8. Sugar Methods Sugar specific methods
HPLC – fructose, glucose and sucrose
Enzymatic – fructose, glucose (and sucrose as glucose)
FTIR
Non-specific methods
reducing sugar methods (Lane-Eynon and Rebelein)
over estimate sugars content
interference from non-sugar reducing substances present in wine (tannins & polyphenols)
Note : Sugar-free extract values calculated from erroneously high sugar results are erroneously low.

9. Summary Conclusions Clarify the meaning of ‘RS’ when used.
Report residual sugar as sum of glucose, fructose, and sucrose in g/L wine.
Use methods specific for wine sugars, avoid those that also test for reducing substances.
Avoid reporting sugar alcohols, such as glycerol, as a sugar.
Avoid testing for sugars not expected in wine
- maltose
- lactose