Pre-Prohibition pilsner contains up to 30 percent corn, and chicha de jora, a low alcohol beverage indigenous to the Andes, is brewed exclusively from maize.
But if your beer tastes like corn and hasn't been anywhere near a stalk, you may have an issue with dimethyl sulfide.
Dimethyl sulfide (DMS)—(CH3)2S—is a compound that’s commonly described as having the aroma of cooked corn, or even boiled cabbage. DMS is fairly common in light lagers, even appropriate in small amounts, but its presence is usually considered a flaw. It has a very low threshold of detection, so even small amounts can overwhelm the palate.
DMS begins in the malt house. A precursor compound called S-methylmethionine (SMM) develops during the germination of barley and is therefore present to some degree in all malt. But because SMM is vulnerable to heat, it is largely driven off during the kilning of pale, crystal, and roasted malts. Very pale malt like pilsner, however, still contains appreciable amounts of SMM, which breaks down into DMS when exposed to the heat of the boil.
That same heat, however, is your best defense against DMS in the final beer because evaporating water carries DMS away with it. So a long, rolling boil will drive away DMS as it is produced. But quickly chilling the boiled wort is essential because sub-boiling heat will continue to promote the conversion of SMM to DMS without the benefit of steam to take it away.
So, to minimize DMS in your homebrew, observe the following precautions:
- Boil the wort vigorously for at least 90 minutes, especially if the grist is mostly pilsner malt. Some brewers recommend boiling for up to two hours for all-pilsner beers.
- Aim to boil off at least 10 percent of the original volume.
- Never cover the boil kettle, even during the chilling process. Condensation can gather on the lid and return DMS to the wort.
- Chill the boiled wort as quickly as possible to minimize further conversion of SMM to DMS.
Bacterial contamination can also create dimethyl sulfide. But your best defense in this case is—as always—to follow excellent sanitation practices.