Dimethyl sulfide, or DMS, is a set of compounds that give some beers character of cooked corn or creamed corn which is noticeable in the beer's aroma and flavor.
DMS in Beer
Some detectable level of DMS is characteristic of many lager styles, and is especially noticeable in light lagers. However, DMS is present in most beers at some level. It is excessive DMS that gives some home brewed ales a "cooked corn" character.
Causes of DMS
DMS is created whenever wort is heated, by the breakdown of precursors found in pale malts. Under ordinary circumstances, most of the DMS that is created by heat is then evaporated during the boil. Some DMS is also removed during vigorous ale fermentations, which is why higher levels are often found in lagers.
The most common causes of excessive DMS in finished beer are:
- Covered boil
- Covering the brew kettle during the boil prevents DMS from evaporating, and results in high levels of DMS in the finished beer. Leave the boil uncovered to reduce the levels of DMS.
- Slow cooling
- Because DMS is created at temperatures below boiling, cooling the wort too slowly means that excessive levels of DMS can be created which cannot be evaporated once the boil has stopped. Cool the wort faster to reduce the levels of DMS.
DMS is naturally present in relatively high levels in many beers. There is no easy way to add DMS character to a beer artificailly, but to increase levels during brewing, simply cover the wort for part of the boil, taking care to avoid boilovers.