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Possible Mash Infection, Need Help


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Denver Distiller - Thanks.  Get your points related to the fact that this NOT beer making with a boil.  But going back to read his mash protocol, my thought was that he was depleted of 02 and getting a stuck lag phase.  Or he could pitch at a higher rate?   Your point I think here is that he needs to get to fermentation ASAP... and so a shorter lag phase would be preferable.  Makes sense.

I know that I have had some bourbon mash fermentation problems with butryc acid hits that seemed to be remedied with a shot of O2 in the mash before the pitch.   But I also upped my pitching rate at the same time.... breaking my rule to control change variables given the interest to prevent having to discard another bad mash run. 

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  • 6 months later...
  • 5 months later...

Reading this (now dated) tale of woe leads me to a few thoughts.

The off-flavor was never identified with enough specificity.   "Skunky" suggests sulfur compounds, Tim-O-Tees description sounded more like a classical phenolic flavor, acrolein in quantity would certainly be off-putting but unlikely to be described as either "skunky" or "band-aid", 4-VG & 4-VP are phenolics, and in quantity may suggest "band-aid", but there are other phenolic compounds that would sooner cause such flavors. 

Then there is the long & circular discussion of infection, which are not well evidenced.

A half hour with a microscope & a gas-chromatograph would be definitive wrt to these theories.

I am inclined to accept Tim's description of phenolic/band-aid flavor.  The chances that bacterial infections are so prevalent as to create this flavor reliably despite acceptable sanitation and  pitching rates is difficult to accept.  Needs labwork, not guesswork.

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  • 4 weeks later...

Thank you for the insights everyone.  I have not yet eliminated this "problem" but have seemed to be able to minimize it somewhat.   Stevea- Assuming that these are phenolic compounds, what are some common scenarios that would produce these?  I do use malted barley in most mashes but have experienced these flavors in all corn mashes as well.  Is it strictly unwanted bacteria that would cause this or is there something happening to my yeast that would cause them to produce phenolics? Can something happen in the still that would do this?

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Second brett as being a negative phenolic contributor.  I think it's the 4-VP that's the major standout in distilled spirits, not so much 4-VG, but that's just my personal opinion.  4-VP is burnt plastic bandaids and bad hospital smell.  4-VG is more of a rye spice.

However, do not discount POF+ yeasts, especially with high malt barley and wheat mash bills (high ferulic acid).


A good primer is to look at the processes to emphasize phenolics/clove in Wheat Beers, and don't do anything they tell you to do.


I think ultimately, the easy answer for distillers, is to mash in malt at a higher temperature than you might be comfortable with, and utilize exogenous enzyme to ensure complete conversion, combined with a lower fermentation temperature.  Don't add malt or wheat as an adjunct before cereal mashing/gelatinization of corn (some do this for the enzyme).  Also experiment with unmalted wheat, if you are using wheat, or really any unmalted adjunct. And try to stay away from POF+ yeast (finding out if your strain is POF+ or - may not be easy) - but if you are playing with beer yeast, specifically ale or hefe, it's there.

Back to the Brett - it creates the volatile phenolic flavors the same way that POF+ yeast does, so anything you do to minimize ferulic acid production is going to limit the phenols from a Brett infection as well.

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I guess a more appropriate question would be how do I manage Brett?  What implications will increasing yeast pitch rate have? And on the malted barley subject, is there a temp that would be too high to add malt that would have negative effects on flavor?

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Malt contains plenty of both alpha and beta amylase. Typically brewers and distillers use the temperature they rest the grain at to determine which is more active. I believe Silk is recommending mashing in hotter to reduce phenols from the malt. However, if you mash them in hotter you lose some Diastatic Power, because the beta amylase is being denatured faster at that higher temperature, so he is also recommending using added enzymes to complete the conversion. I'm sure Silk is much smarter than me though so I could be misunderstanding, but maybe a simpler interpretation from a dummy will help.

As far as Brett goes. The idea is to keep it from growing in the first place. With a healthy ferment and a high pitch rate, the yeast very quickly lower the Ph and sugar available, and raise the alcohol %, making it a much less hospitable environment for bacteria.

I believe Silk and Steve are talking about 3 different possible sources of phenols, one from your grains, one from your yeast, and one from a Brett infection. They can correct me if I'm wrong.

I really feel for you if you're still tackling this a year later though.

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  • 2 months later...

Bringing this one back from the dead. I'm getting a sulphur smell towards the end of my stripping runs off of this rye/wheat ferment. I am not surprised, as this mash/ferment went less than ideally. We got good conversion, however. My question is this: in polishing these low wines, should I be concerned about this sulphur smell bleeding into my hearts cut, or will it just mean a bigger, smellier tails cut? Thanks in advance folks 🤙 


Any idea about this @Silk City Distillers ?


No foul odors came over to the polishing run. We have ample copper contact in our still that must've taken care of it.

Edited by kleclerc77
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