Influence of some technological parameters on the formation of dimethyl sulfide, 2-mercaptoethanol, methionol, and dimethyl sulfone in Port wines

Volatile sulfur compounds of 15 young port wines and 12 old port wines were determined. As there is a great difference in the pool of sulfur compounds between the two groups of wines, an experimental protocol was performed to determine which technological parameter (dissolved 0₂, free SO₂ levels, pH, and time/temperature) was related with the formation/consumption of these compounds. Four sulfur compounds were selected for this purpose: dimethyl sulfide, 2-mercaptoethanol, dimethyl sulfone, and methionol. The synergistic effects of increasing temperature and O₂ at lower pH had the largest impact. Dimethyl sulfide was formed during the experimental period in the presence of O₂. Dimethyl sulfone had the same behavior. Methionol decreased significantly in the presence of O₂, but no methional was formed. 2-Mercaptoethanol, considered to be an important "off-flavor" in dry wines, also decreased during the experimental period (54 days) in the presence of ₂, and the respective disulfide was formed. These results corroborate the fact that old port wine (barrel aged) never develops "off-flavors" associated with the presence of methionol (cauliflower), 2-mercaptoethanol (rubber/burnt), or methional (cooked potato). In fact, temperature and oxygen are the major factors in the consumption of these molecules. However, some notes of "quince" and "metallic" can appear during port wine aging, and these can be associated with the presence of dimethyl sulfide.