What the hell is that about DMS and why should you pay attention to it?

The next time you enjoy a beer, have you noticed that touch of corn or rotten egg? You’re probably sniffing something called Dimethyl Sulfur, or DMS, which although sometimes can be an ally in making, at other times is an unwanted friend. Understanding its origin and how to handle it can make a difference in the quality of your beer, after all, who wants a scent that looks like a breakfast in the trash?

The way of the DMS: from the malt to your glass

This chemical compound is formed in the belly of barley during its germination and drying process. In essence, all malts contain an amino acid called SMM, which functions as the raw material for the creation of DMS. But do not be alarmed, it is not that the malt is angry, but that process is natural and, in some styles, even desirable. The key is how we control the conversion and evaporation of DMS to keep it at acceptable levels.

How does the SMM happen to become DMS in your pot?

When you heat the malt, the SMM begins to break down into DMS and another compound called DMSO. Temperature and time are the best friends of this process. If you boil the must with intensity and for long enough, the DMS, which is very volatile, tends to escape. To give you a concrete idea: in 40 minutes, more than half of this compound can disappear if you keep a good boiling. Therefore, the most experienced brewers usually recommend boiling at least an hour and a half, preferably without covering the pot to facilitate evaporation.

The art of controlling the DMS: from pot to bottle

But the story does not end here. Although most of the DMS is lost during cooking, an open secret in making is that this compound can continue to appear even after cooling the must. Why? Because yeasts, especially those that ferment at lower temperatures and in lager styles, can produce DMS during fermentation, from the residual DMSO. By rapidly cooling the must, it prevents more DMS from forming at that sensitive stage.

The scent of DMS: friend or enemy?

A smell of cooked corn, rotten egg or even a smell of burnt onion can tell that your beer contains too much DMS. However, in some dark styles or with strong flavors, such as maltose and robust beers, that aroma can be masked by toasted notes, chocolate or caramel, making it not such a visible problem.

Tips for a beer without unwanted DMS

[‘Use two-row malts instead of six-row malts, as they contain less MMS.’, ‘Pay attention to the type of base malt; pale malts tend to have higher levels of MMS.’, ‘Avoid using ingredients that can increase DMS levels, such as corn, if you are looking for a clean product.’, ‘Boil the must for at least 90 minutes, without covering the pot to allow the DMS to escape in excess.’, ‘Reduce the temperature after boiling as soon as possible and cool quickly.’, ‘Be aware that yeasts can produce DMS during fermentation, especially in lagers, so control at that stage is also key.’]

What about DMS in different beer styles?

Not all beer is the same compared to DMS. Light lagers and pilsen are the most sensitive, showing aromas that can ruin their delicate profile if they are not controlled well. Instead, in beers such as Stout or Strong Ale, their presence passes almost unnoticed, covered by toasted and sweet notes. The choice of ingredients and techniques greatly influences how DMS presents itself, and ultimately, how our smell perceives it.

The DMS: Hidden Friend in Beer Production?

Not everything is a problem, sometimes in small quantities, the DMS can bring some aromatic complexity, especially in styles with deep maltose profile. The key is to keep that proportion under control and not to be fooled by momentary aromas that can dissipate over time in bottle or barrel. Experience and technique are your best allies in this delicate aromatic game.