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DMS and Diacetyl

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  • DMS and Diacetyl

    Hey y'all,

    I've got an interesting problem. I work in a place that makes a unique product. We do kombucha based beer, I was hired in to help get some QC issues under control, primarily we're dealing with DMS and Diacetyl. To give an idea of our process we mix strong kombucha culture with RO water, add a bunch of sugar, hops, other ingredients, and yeast. We don't and have no ability to boil, and everything is in open top fermenters or old barrels, so I have my work cut out for me. I've introduced as many quality controls for sanitation as I can, but the fact is that we are still in open top fermenters (with cloth over the top), so I can only control so much exposure. Apparently these off flavors are a more recent development, so it hasn't been an issue for the several years they've been in business. We stir in cane sugar up to about 13 Plato, we start at about 3.8 pH with the water/culture mixture, we soak all fresh ingredients in 185F water, otherwise ingredients are frozen. We aren't oxygenating but will soon. We've been using a mix of wine and british ale yeast, I'm looking to cut out the ale yeast to see if the diacetyl leaves, but I still have DMS presenting. Are there specific bacteria I can be looking for that would be producing the DMS? We've been sending out our cultures from bad batches for testing and so far are coming back negative for most spoilage organisms. The kombucha itself is fine and doesn't present any off flavors, so I'm worried its something in the air, or some of the ingredients.

    Kombucha is made with a pretty complex symbiosis of organisms, so I'd like to try and narrow down the ones that might be giving us a problem, and our reports have come back negative for a lot of pedio and lacto strains that may cause problems. The DMS is what is the most confusing.

    Side note: I'll pull a sample from the tank and run a diacetyl test with no issues, but after transferring diacetyl and DMS will be super obvious. I've never known those off flavors to stratify in the tank. Temperature runs pretty consistently throughout the tank between 68-73F depending on where it is in the brewery.

    If anyone has any ideas, I'd be much obliged. Thanks!

  • #2
    I had a rep send me samples of a product that's added at the beginning of fermentation which blocks the pathway that yeast use to create the VDKs (alpha-acetolactate and diacetyl). I've never used it, but was considering it for our lagers. The company's name is J. Tech Sales out of Boca Raton, FL. Phone number is 888-801-8809. No idea how to reduce your DMS though. Good luck!
    Peter Landman | Brewmaster | Seabright Brewery | Santa Cruz, CA


    • #3
      I think it is likely not your yeast doing this. Both yeasts you mention would not readily produce these flavors on their own if proper temperature is used. Even with lager yeasts, good temperature controls with the appropriate ramps can get lager yeast to metabolize the diacetyl that they make very quickly at the end of fermentation. If I had to guess, I would say that you likely have an infection from pediococcus and probably a sulfur producing bacteria as well. Brewers yeast will not make DMS, in brewing that is a product from malt. Pedio will make a ton of diacetyl, and I have read about but have no experience with DMS producing bacteria. So I would first do some plating and find out what it is you have growing in your product. As far as the diacetyl coming in later on in the process, yeast and bacteria don't directly produce it, rather with temperature and oxygen acetolactate is converted into diacetyl. When you take a sample, try doing a forced diacetyl test, the procedures are all over the place for this. Otherwise, you need to run it through a GC or do a VDK test with an IR spec to find out if you have any acetolactate or diacetyl in the product before you cool it. Your fermentation temperatures that you listed should not leave diacetyl in the beer if it is allowed to fully attenuate. Especially with open top tanks.

      Just thought of this as well, you don't use any malt to get your sugars, so aside from not really being "beer", you do not get any of the FAN from the malt that brewers normally would. Valine is a very important amino acid for yeast more importantly, yeast will make valine if there isn't enough in the wort. The process for doing this has a byproduct, acetolactate. So without the proper nutrients for the yeast, you will drive the production of diacetyl. So you should send out a sample of your base that hasn't been inoculated with the scoby yet.
      Last edited by jebzter; 11-10-2017, 10:52 AM.


      • #4
        You are correct in that yeast can reduce DMSO to DMS, however, no yeast directly produces DMS, so in a beverage with no malted barley in it, it would be impossible to get DMSO to convert unless it was being added another ingredient that was not mentioned or there is an infection producing it. No malt means no SMM, further the product isn't even boiled, so SMM wouldnt convert to DMS or DMSO for that matter.


        • #5
          Originally posted by WaterEng
          Good points, excepting that the original post didn't mention what other non-tea ingredients are in the kombucha. Malt is not the only source of SMM. SMM is widely found in a variety of fruits and vegetables. So maybe there is still some SMM contributed to the beverage? While I don't believe that kombucha is boiled or heated to any great degree, its important to note that SMM conversion to DMS is a heat-driven reaction. But that does not mean that the wort has to be boiling. As long as the wort is at a temperature above the activation temperature for the SMM-DMS reaction, it will occur. The difference is that the lower temperature reaction rate will be less than if the wort was at a higher or boiling temperature.
          Currently, our process involves no boiling at all. Water being added was about 70F from our RO unit until recently switching to 85F carbon filtered water. The non-tea products we use that get heated are fresh ginger which gets a 185F soak before processing. We also use sliced peaches, elderberries and raspberries, all of which come frozen. We will deforst them before adding them to solution. Tea is steeped for 2 hours at 185F. We also add oak chips in muslin bags, those are not treated, but the bags are soaked in sani prior to use. One part of the process that I am trying to get changed (owners are not super open to change) is that we add all these extra ingredients at the beginning of fermentation. So we scrub a lot of the flavor out, but also leave ourselves open to contamination early on.

          The fact that these problems are not consistent, but are consistently the off flavors that present, and only surfaced in the past year, makes it a bit of a mystery. I'm wondering if it's a new bug in the air, if something is surviving on the fruit through freezing, if something is on the oak chips......I guess I don't know why it would start becoming a problem now when it didn't seem to be a problem for them in the past, especially with a relative lack of sanitary practice. I know some people have gotten away with bad practice for a long time before it's come back to bite them, but I've had this problem recently with batches I've instituted new sanitary practice on.

          And again, the fact that I can pull samples from the top and the bottom and run a forced test without any evidence of off flavors and then have them present after a transfer is super weird, I've never experienced anything like that in the beer world. As far as I know those compounds don't just hang out in the middle of the tank.


          • #6
            Where is your brewery? I'd be interested in checking out your website.


            • #7
              If it presents after transfer, I'd look at hoses, pumps, and anything product touches during transfer.


              • #8
                Originally posted by ipaguy View Post
                If it presents after transfer, I'd look at hoses, pumps, and anything product touches during transfer.
                It presents immediately after transfer. I've been pulling a sample to test it right after we move finished product to packaging tanks. We noticed that samples prior to transfer wouldn't present off flavors, and after we crashed they would. This isn't unheard of obviously. We only have the ability to do diacetyl tests by heating up samples, and we'll pass them around to 4-5 people to get feedback from different pallet sensitivities. Even if it passes the taste test, it will be super noticeable literally right after transfer at room temp in the packaging tank, so it's not an equipment issue, I don't think anything would have enough time to produce that amount of compounds during a transfer. It's a strange phenomenon.