Off Flavors: DMS

I popped open a bottle of batch #11, my all grain wheat recipe from Brewing Classic Styles. I thought this batch was a disaster, at first because I overpitched, then because I thought it overattenuated, and yet again when I thought it was infected.

Things have definitely changed. It is by far the most beautifully pale beer I've ever made. The head is huge and fluffy and lasts forever. Before stirring up the yeast, it was beautifully clear. It looks great in my hefeweizen glass. The flavors are definitely different than my first wheat; my last one tasted very much like banana. This one doesn't taste like banana at all. Instead it has a spicy flavor and something else that is slightly funky that I can't put my finger on.

And one more thing.

It tastes slightly like cooked corn.

Sure, it is subtle. But I'm pretty sure it's there. Cooked corn flavor. I looked over my records, and I only boiled 60 minutes.

Listen up kids, here's the lesson for today.

Always boil any recipe with a significant percentage of pilsner malt for a minimum of 90 minutes!!!

DMS stands for Dimethyl sulfide. It has a pretty low taste threshold and tastes like cooked corn. The more lightly kilned a malt is, the more DMS precursors it has in it. A 60-minute boil is generally enough to drive off all DMS from darker malts like 2-row. Pilsener malt, however, is as light as you can get, and thus produces a ton of DMS when boiled.

What do I mean by 'drive off'? DMS precursors turn into DMS when heated. However, this is counteracted by a 'vigorous' boil. As it is created, the DMS is circulated up to the top of the water and driven off into the air. This only works if you have a rolling boil and you do not cover your pot while you boil. If you ever wondered why all the literature tells you to have an uncovered, rolling boil, now you know. It doesn't have to be leaping up at you, but the water has to be circulating in the pot and evaporating. For a pilsener malt, it takes at least 90 minutes to get all that stuff out of your wort.

Now I have a bunch of corn hefeweizen. Oh well, I'm probably the only one who can taste it. Besides, I boil *all* my beers for 90 minutes now in order to have more water for sparging.

Note: You can supposedly get DMS from cooling to slowly. I cool via ice bath, and have never had a problem with DMS before. Also, some people practice a no-chill method of cooling wherein they leave their wort overnight in a sealed container to cool. I haven't run into DMS from using an ice bath, but be aware that it is *possible* to end up with DMS in your beer if your cooling method is too slow and you use very light malts.