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Thread: Boil off DMS after present in solution?

  1. #1
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    Boil off DMS after present in solution?

    I have a fairly unique situation that I'm curious if I can resolve.

    I was making a kettle sour the other day and our heating elements were accidently left on after we cooled to 110* and pitched our lacto culture.

    When I came back to the shop around 10:30 that night I had a giant mess on my hands and about 1.5bbls less wort in my boil kettle.

    I let the wort cool over the next day and then we pumped back into the mash tun, cleaned our boil kettle and heating elements and then moved the wort back, brought it up to 185* for about 25 minutes and the dropped temp back down to 110* and pitched a new lacto culture.

    Now during that slow cool there was created the inarguable presence of DMS. What I'm curious about here is when I bring this back up to boil tomorrow to finish my beer will I be able to boil off that nasty creamed veggie taste that's in there from the DMS or is it that that once the DMS is present I'm stuck with it?

    Thanks in advance for any help.

  2. #2
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    generally when wort is heated near boiling temperatures, the dms precursor is converted to dms. As you boil you drive off the dms. Normally you would want to boil long and vigorously enough to convert all of the dms and drive it off.

    if you have heated your wort and created dms you should be able to boil it to get rid of it.

  3. #3
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    Quote Originally Posted by beerme View Post
    generally when wort is heated near boiling temperatures, the dms precursor is converted to dms. As you boil you drive off the dms. Normally you would want to boil long and vigorously enough to convert all of the dms and drive it off.

    if you have heated your wort and created dms you should be able to boil it to get rid of it.
    Great to hear, thanks for the response!!

  4. #4
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    Thirty minutes of open boiling is sufficient to significantly decrease DMS from wort (Wilson and Booer, 1978). The reason we boil longer than that is because the conversion of SMM to DMS takes quite a bit more time. Since that wort has probably been heated more than long enough to convert all SMM to DMS, an additional 30 minute boil will be sufficient to expel all your existing DMS.
    WaterEng
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  5. #5
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    Quote Originally Posted by WaterEng View Post
    Thirty minutes of open boiling is sufficient to significantly decrease DMS from wort (Wilson and Booer, 1978). The reason we boil longer than that is because the conversion of SMM to DMS takes quite a bit more time. Since that wort has probably been heated more than long enough to convert all SMM to DMS, an additional 30 minute boil will be sufficient to expel all your existing DMS.
    The half-life of the SMM to free DMS conversion is 32-38 minutes depending on wort pH, at boiling (C.J. Dickenson, 1979). This is why 60 and 90 min boils are common. At 60 mins you have halved twice (roughly), and at 90 you will have halved three times, eliminating almost any DMS that could have been converted from SMM. If there is unconverted SMM left at the end of boil, re-formation of free DMS can occur as temperature drops.

    S. Cerevisiae can convert DMSO (another precursor, one which survives boiling) into free DMS in later stages during fermentation. SMM is not converted by yeast. Although typically less than 25% of DMSO will be reduced by yeast, and maybe as little as 4-5% converted to free DMS, this can still lead to significant levels of free DMS in the finished product. Anness and Bamforth wrote a great review of DMS in Journal of the Institute of Brewing July-Aug 1982.

  6. #6
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    Quote Originally Posted by UnFermentable View Post
    The half-life of the SMM to free DMS conversion is 32-38 minutes depending on wort pH, at boiling (C.J. Dickenson, 1979).
    At what temperature does the conversion from SMM to DMS begin? My understanding is that beyond the threshold, the reaction proceeds faster at higher temperatures.

  7. #7
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    Quote Originally Posted by beerme View Post
    At what temperature does the conversion from SMM to DMS begin? My understanding is that beyond the threshold, the reaction proceeds faster at higher temperatures.
    I'd have to dig a bit deeper on the subject to give you the exact answer, however I believe that Lewis and Bamforth in Essays in Brewing Science had stated 176*F (80*C) for conversion of SMM to DMS. Some others have been quoted as saying 60*C is where conversion begins, 70*C is the point of rapid conversion. I don't remember the references for those off hand, but I feel like I saw it a few places.

    C.J. Dickenson states that with a 6*C drop in temperature (from the boiling point of the wort), there will be a doubling in the half-life of conversion of SMM to DMS. The 32-38 min half-life is at the most rapid conversion rate (boiling). DMS itself boils at 99*F (37*C) and thus is evaporated as fast as it can be converted. The 60, 90, 120 min boils are for the conversion of SMM and not actually to "boil off" DMS. As stated earlier, 30 mins is sufficient to significantly reduce DMS in wort (provided the SMM has already been converted to DMS).

    My anecdotal experience tells me Lewis and Bamforth are probably correct, as I have brewed a no boil, kettle soured Berlinner Weisse with a majority of lightly kilned Pils malt. The temperature reached as high as 75*C for pasteurization, but never above 80*C as to avoid the need to boil off DMS. I am fairly sensitive to DMS (very sensitive by most standards) and was very happy with how clean the beer came out. I could not detect any DMS at all, and no mention of it from about 30 other brewers who were at the release.

  8. #8
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    Quote Originally Posted by beerme View Post
    At what temperature does the conversion from SMM to DMS begin? My understanding is that beyond the threshold, the reaction proceeds faster at higher temperatures.
    That is correct, 80C is shown as the temperature at which meaningful conversion of SMM to DMS begins. The conversion reaction rate is temperature-dependent, therefore your actual boiling temperature will influence the rate. Brewers working at higher elevation, are likely to have to conduct longer boils to convert most SMM to DMS. The intensity of the boil does not have any effect on the rate of SMM to DMS conversion since boil intensity does not alter the temperature of the boil.

    Unfermentable correctly points out that the half-life conversion rate for SMM to DMS is about 30 minutes. However, that is not applicable in the OP's case. All SMM should have been fully converted to DMS by the extended boil. The OP just needs to volatilize the latent DMS out of the wort. A 30-minute boil is sufficient to expel all DMS from wort when all the SMM has already been converted. This is especially salient when you consider that pale malts (2.5L to 4L color rating) have very little SMM but do have significant DMS content in the kernels. Then a shorter boil can be employed with that slightly darker class of malt. Its the pils class of malt (1.2L to 2.2L color rating) that brewers need to pay keen attention to SMM and its resulting DMS content.
    WaterEng
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