DIMETHYL SULFIDE (DMS) Table I lists some basic properties of DMS.
Table II lists types of beers in order of their perceived threshold of DMS. Those with the lowest thresholds are most likely to have off tastes at excessive DMS levels.
The perceived flavor intensity can be expressed as follows where P is the perceived flavor intensity, C is a concentration of DMS in beer, and T is the taste threshold in beer:2
P = (beer style constant) = ( C/T ) n
Table III shows typical amounts of DMS and SMM in a finished malted barley kernel.1
The level of DMS in unmalted barley, wheat, rye and corn syrup is negligible.
The amount of DMS in corn grits has been reported to be approximately 0.4 ppb.1
Essential oils of hops contain small levels of DMS but are steam stripped from the boiling wort.5
Some typical levels of DMS and SMM in different varieties of malt are shown in Table IV.4
The level of SMM in malt is responsible for the DMS level in wort. During mashing the SMM, DMS and very soluble DMSO are brought into solution. No SMM is hydrolized to DMS at this time.
Kettle boiling hydrolizes SMM to DMS which is removed during evaporation. The half life or time needed to remove half of the DMS is 40 minutes so that three-fourths is removed in 90 minutes. Narssis recommends a 100 minute boil to reduce the level of SMM and DMS to acceptable levels in most beers.2
The DMS produced during the hot wort stand will stay in solution even if the hot wort tank is vented. For every extra hour of hot wort stand, a DMS increase of approximately 30% will result. The level of DMS in the wort determines the level of DMS in finished beer. In order to predict the level of DMS in finished beer Table V shows the relationship between SMM in malt and DMS in beer.
The yeast's metabolism does not convert SMM to DMS but certain yeast can produce higher DMS levels by reducing DMSO to DMS, especially in lager beer production at cooler temperatures. Certain wild yeasts and Enterobacter agglomerans can produce DMS.5 Table VI shows the reactions that take place in malting and wort boiling.
After fermentation, no change in DMS level occurs unless some form of purging or contamination occurs. Water dilution of high gravity beers may reduce the perceived threshold of DMS due to dilution of other mashing flavors.
TABLE I PROPERTIES of DIMETHYL SULPHIDE Dimethyl Sulfide (DMS)
(CH3)2S
H3C-S-CH3
Boiling Point: 99oF Density: 0.848
Flavor Threshold (Beer): Perceived Threshold: 10-150 ppb Depends on amount of flavor in beer
Flavor: Cooked corn, creamed corn
Aroma: Same - highly volatile
Source: Precursor in malt (SMM), hops (minor)
TABLE II PERCEIVED THRESHOLD of DMS on VARIOUS BEERS Lagers (lowest):
- Low adjunct beers with low gravities or diluted flavor.
- High adjunct beers with corn grits
- High adjunct beers with other adjuncts
- Low to medium gravity (1.040-1.048) beers - all malt
- All malt German or higher gravity, light colored - flavored beers
- Amber - dark flavorful beers
Ales (highest):
- British light ales
- American or British amber or dark ales
- Stouts or strong flavored beers
TABLE III DMS and SMM LEVELS in TYPICAL MALTED BARLEY KERNEL MALT KERNEL DMS (ppb) SMM (ppb) 1) Husk 0.81 0.67 2) Starchy Endosperm 1.5 1.2 3) Embryo and Scutellum 5.9 2.2 4) Crospire 15.0 14.0
- (Biosynthesis activity 2-4)
TABLE IV REPORTED DMS and SMM LEVELS in DIFFERENT MALT VARIETIES MALT KERNEL DMS (ppb) SMM (ppb) SMM (ppb)
- Larken 12.9 12.0 24.9
- Proctor, Pale Ale 7.1 3.7 10.8
- Klages (2 row) 9.2 2.0 11.2
- U.S. Malt: (high modification, low kilning temperature)
- British Malt: (moderate modification, higher kilning temperature)
An American maltster reported that typical combined DMS/SMM levels in North American brewers malt averaged 10-15 ppb. But during years of high protein levels, for example the '88 drought, levels may approach 20 ppb.
TABLE V SMM LEVELS in MALT vs. DMS in FINISHED LAGER BEER MALT BEER % INCREASE
SMM (ppb) DMS (ppb) (SMM to DMS) 3.2 38.0 1090 4.6 61.0 1200 6.0 78.0 1200 8.4 98.0 1070
TABLE VI REACTIONS CONTRIBUTING TO DMS FORMATION
(CH3)2S-CH2-CH2-CH(NH2)-COOH(CH3)2 + OH >(CH3)2S<(oxidation/reduction)>(CH3)2S=O S-Methyl methionine Dimethyl sulfide Dimethyl Sulfoxide SMM DMS DMSO
Infromation from http://www.abtonline.com
