Low molecular weight sulfur compounds

What’s that horrible smell?

Low molecular weight sulfur compounds, such as hydrogen sulfide and mercaptans, are responsible for many undesirable attributes in wines such as rotten eggs and burnt rubber characters typically described as ‘reductive’. Created primarily by stressed yeast cells or changes in sulfur chemistry in a small percentage of wines bottled under low oxygen transmission rate closures, these sulfur compounds can impart significant sensory impact to a wine even if present at trace levels.

Thanks to some new technology and months of research and development at the AWRI, the Commercial Services group now has the ability to identify and quantify a number of key compounds responsible for the production of these reductive aromas in wine. Knowledge of these compounds, listed in Table 1, can play an important role in determining the source and extent of the problem and help winemakers manage strategies to prevent their formation.

Reductive characters in wine can be associated with some, or a combination, of the compounds listed in Table 1, elevated above their sensory thresholds. The most common offenders include hydrogen sulfide, mercaptans or thiols, disulfides and dimethyl sulfide. All compounds in the assay are analysed to concentrations at or below their respective sensory threshold.

Table 1 Suite of quantifiable low molecular weight compounds

Compound Odour Descriptor Aroma Threshold (µg/L) Typical range (µg/L)
Hydrogen sulfide Rotten egg, sewage like 1.1 – 1.6 0 – 370
Methanethiol Rotten cabbage, burnt rubber, putrid 1.8 – 3.1 0 – 11
Ethanethiol Onion, rubbery, burnt match, sulfidy, earthy 1.1 0 – 50
Dimethyl sulfide Blackcurrant, cooked cabbage, asparagus, canned corn, molasses 25 0 – 980
Carbon disulfide Sweet, ethereal, slight green, rubber, sulfidy, chokingly repulsive >38 0 – 140
Diethyl sulfide Garlic, rubbery 0.9 0 – 10
Methyl thioacetate Sulfurous, cheesy, egg 50* 0 – 115
Dimethyl disulfide Vegetal, cabbage 29 0 – 22
Ethyl thioacetate Sulfurous, garlic, onion 10* 0 – 180
Diethyl disulfide bad smelling, onion 4.3 0 – 85

* In beer

Prices per analysis
No. of samples 1-7 8+
Cost/sample (excluding GST) $185 $140
Samples for analysis should be submitted in well-sealed containers with minimal headspace and a minimum volume of 200 mL.

For more information, please contact AWRI Commercial Services on (08) 8313 6600 or e-mail commercialservices@awri.com.au