More on DMS

Discussion in 'General Brewing Discussions' started by Nosybear, Jul 12, 2018.

  1. Nosybear

    Nosybear Well-Known Member

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    Was reading a brewing science textbook by Charles Bamforth yesterday and came across this on the subject of DMS:

    "SMM is heat -sensitive and is broken down rapidly whenever the temperature gets above 80 degrees C during the process.... If the boil is vigorous, most of the SMM is converted to DMS and driven off (The half life of SMM at 100 degrees C is 38 minutes, and this value doubles for every 6 degree C decrease in temperature)."

    In Denver, where I brew at 6,000 feet, the boiling point is 200 degrees F, or about 93.3 degrees C, meaning the half-life of SMM in my boils is 72 minutes - I reduce the SMM in malts by half in just over an hour. The flavor threshold of DMS is 30 parts per billion. So my friends, this is about the best argument I can find for keeping my 90-minute boils when using Pilsner malt. I'll also keep 60 for those using pale ale and standard two-row malts. The same book mentions other means of controlling DMS but they seem to be beyond the homebrewer in terms of technology and measurement required.
     
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  2. J A

    J A Well-Known Member

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    I'm sticking to the program as well. Besides, that extra 30 minutes of boil time is when I weigh out hops, start cleaning the mash tun, re-route plumbing to set up for wort chilling and have a cold beer. That's quality time in my brew day! :D :D :D
     
  3. KC

    KC Active Member

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    Good point about altitude. I've never brewed higher than 300ft, and boiling point is 215 with a condenser.

    I wish SMM content was part of a malt analysis sheet. Then we'd know where it sits in terms of the perception threshold.
     
  4. Nosybear

    Nosybear Well-Known Member

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    As I said in another thread, a 60 minute boil is a risk management tool. You may not get DMS with a shorter boil, you may. At 60 minutes the likelihood becomes very small that enough SMM would survive to yield perceptible amounts of DMS (30 micrograms per liter, or parts per billion).
     
  5. BoomerBrian

    BoomerBrian Active Member

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    I have done 60 minutes pilsner boils but generally chicken out and just go 90. I couldn't really detect any dms but I can't say it wasn't there. I know a guy that is very sensitive to dms. Should have had him try it.
     
  6. The Brew Mentor

    The Brew Mentor Well-Known Member

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    How much is based on boil off rate? I've never had any issues but I boil off 4 gallons/ hour.
     
  7. Nosybear

    Nosybear Well-Known Member

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    Dr. B. just talked about temperature. Boil-off rate wasn't mentioned.
     
  8. J A

    J A Well-Known Member

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    #8 J A, Jul 13, 2018
    Last edited: Jul 13, 2018
    I imagine that boil-off rate would be relevant in that boil vigor will insure that DMS is driven off energetically. A simmer would produce a lower boil off rate and could leave some DMS in the wort.
    How big a vessel? Rate would be relative to size of the pot. Four gallons per hour sounds huge to most home brewers but on a sizeable system, it may not be much.
    I boil energetically for 90 minutes and lose 2.5 to 3 in a 15 gallon pot.
     
  9. The Brew Mentor

    The Brew Mentor Well-Known Member

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    When I was doing 15.75 gallon batches, I was @ 3 gal/hour.
    I'm now starting my boil with about 38 gallons and lose 4 gal/hour.
     
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  10. Hawkbox

    Hawkbox Well-Known Member

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    I do around 13 gallon boils and lose around 2.5 gallons depending on how close I manage the boil.
     
  11. Ozarks Mountain Brew

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    the wider pot has more surface area which creates a higher boil off rate
     
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