A Novel Ap­proach to DMS Re­duc­tion, Part 1

If you want to brew a very, very, light col­ored 100 per­cent bar­ley beer but are con­cerned about DMS, take heart. In­trepid home­brew ex­per­i­menter has hit upon the idea of a pre-boil “DMS rest.”

Craft Beer & Brewing Magazine - - Contents -

If you want to brew a very, very, light col­ored 100 per­cent bar­ley beer but are con­cerned about DMS, take heart. In­trepid home­brew ex­per­i­menter Tay­lor Caron has hit upon the idea of a pre-boil “DMS rest.”

ASK FOR ANY­ONE’S SHORT list of beer flaws and in­vari­ably you will hear “Dms—dimethyl sul­fide,” bested only by the other D-word “di­acetyl.” Un­like di­acetyl, which is cre­ated dur­ing fer­men­ta­tion, the cause and cure for DMS hap­pen be­fore yeast ever touches the wort.

For those who have never had the plea­sure of en­coun­ter­ing this “fla­vor at­tribute,” DMS is of­ten de­scribed as a cooked-corn fla­vor, but you may also be re­minded of the in­side of a can of black olives or canned tomato paste. If you ever have the chance to taste a par­tic­u­larly po­tent ex­am­ple, you may be able to then find it in a sur­pris­ing num­ber of beers, both com­mer­cially brewed and home­brewed.

DMS is a sul­fur com­pound that is cre­ated by s-methyl­me­thio­n­ine (SMM) some­times called sim­ply “DMS pre­cur­sor.” SMM de­vel­ops dur­ing the ger­mi­na­tion of bar­ley and is there­fore present to some de­gree in all malt. Most of it, how­ever, is

bro­ken down to DMS dur­ing malt­ing and is volatilized dur­ing kiln­ing. The darker the kiln, gen­er­ally the lower the SMM level in the fin­ished malt. Very pale malt such as Pil­sner, how­ever, still con­tains ap­pre­cia­ble amounts of SMM, which breaks down into DMS when ex­posed to the heat of the boil. That makes it tricky to get a Dms-free very light col­ored wort us­ing 100 per­cent bar­ley (us­ing ad­juncts such as corn and rice can de­crease the SMM/DMS load). In this ar­ti­cle, I dis­cuss a novel ap­proach that at­tempts to do just that.

Look­ing for DMS

Re­search sug­gests that DMS is gen­er­ated some­where around 120°F (49°C) or higher but is not volatile un­til about 165°F (74°C) and above. The gen­eral prac­tice to elim­i­nate DMS in­volves en­sur­ing a long and open boil to al­low the DMS to es­cape over 75–90 min­utes and then to chill the wort quickly to be­low the 100°F (38°C). Gen­er­ally this will pro­duce Dms-free beer, but we home­brew­ers with di­rect-fire ket­tles will also see at least some dark­en­ing of the wort in that long boil. The ques­tion arises: can we break down a max­i­mum amount of SMM into DMS be­fore the boil and keep our color low with­out in­tro­duc­ing flaws in the fin­ished beer?

To find out, I first brewed six “DMS train-wreck beers” us­ing dif­fer­ent brands of Pil­sner malt to find the worst of­fender. The good peo­ple in New Bel­gium Brew­ing’s lab, Dana and Jeff, were kind enough to hu­mor me, run­ning them all through their gas chro­mato­graph.

The at­tempt, as shown in Ta­ble 1 (page 66), was an un­qual­i­fied suc­cess. If we con­sider that the ac­cepted thresh­old for tast­ing DMS is 35 ppb, th­ese are all ridicu­lously high. It’s in­ter­est­ing to note that the worst of­fender, Wey­er­mann Ex­tra Pale Premium Pil­sner, is also the one with the low­est Lovi­bond rat­ing. At only 1.2–1.4°L, there is sim­ply more un­con­verted SMM for me to reckon with. It is also mildly in­ter­est­ing that the floor-malted sam­ple is slightly higher than the Rahr, de­spite be­ing kilned a touch darker. Per­haps it has some­thing to do with the pe­cu­liar malt­ing process in­volved. Or per­haps it was just this sam­ple.

Gen­er­at­ing and Vo­la­tiz­ing DMS

Hav­ing iden­ti­fied the worst-case malt, I pro­ceeded to the sec­ond stage of the ex­per­i­ment, which was to try to gen­er­ate as much DMS as pos­si­ble pre-boil and at­tempt to gauge how long of a boil was nec­es­sary to vola­tize it suf­fi­ciently. I used a 100 per­cent Pil­sner malt mash, acid­i­fied for con­ver­sion. Af­ter the usual vor­lauf and lauter, I al­lowed the wort to stand at 160–180°F (71–82°C) for what we’ll call a “DMS rest.”

Af­ter 40 min­utes of DMS rest, I pulled off a quar­ter of the wort and boiled it for 20 min­utes, then cooled it with a cop­per im­mer­sion chiller to be­low 100°F (38°C) in just about 30 min­utes. Then I pulled off an­other quar­ter of the wort every 20 min­utes up to 100 min­utes, and I boiled each quar­ter for 20 min­utes and cooled it in 30 min­utes. Mind you, 30 min­utes is con­sid­er­ably slower than I would nor­mally chill, but my hope was that I would

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