This message was posted by a user wishing to remain anonymous
Considering my experience, it's important to know the technical data sheets from your suppliers, limits of detection of instrumentation, protocol quirks, and areas that are cause for concern or not (such as LAB with or without the hor genes). It's important to reach out to your suppliers if you have questions and to speak to their technical teams. They are usually a serious wealth of knowledge because they spend their whole careers specializing and troubleshooting.
When it comes to dry yeast there are major differences in quality and specifications from one manufacturer to another, this is especially true in the amount of live cells per gram of yeast and contamination. I recently read a blog from BSG on dry yeast quality (Dry Yeast Quality BSG Blog). Although I started on liquid yeast because of the wide selection, I have been pleasantly surprised with my dry yeast recently. After talking with people at meetings, I know many large breweries that have no issues with repitchability of dry yeast nor contamination issues. For use in propagation I hit at least 10 IBU to stop any LAB present in my dry yeast, there are a lot of tips and tricks the suppliers know.
The math/economics about repitching liquid yeast vs dry yeast as single use is not as simple as often presented. This is an area I'd like to explore more.... Back of the envelope calculations look to be if I pitch a brick of yeast into a 10bbl fermentor, then I'm in the ballpark around $10/bbl for fresh yeast pitch without the increased labor/risk/equipment. Liquid yeast is much more expensive and I would argue that no microbial source comes without any risk of contamination or accidental strain swapping or anything else. To me its a no brainer but...
All in all reach out to your supplier.
Original Message:
Sent: 07-11-2025 13:08
From: Kory Davis
Subject: LAB in Dry Yeast
Thanks for posting-this is a valuable observation, especially when you're tracking yeast over multiple generations. Low-level LAB in dry yeast isn't unusual: the biomass is grown in large aerobic fermentors, concentrated, and then fluid-bed dried in rooms that aren't fully aseptic, so a few acid-tolerant cells can survive and gradually accumulate with each repitch. Liquid cultures, in contrast, are propagated and packaged under sterile conditions from start to finish, giving a cleaner starting point and reducing cumulative contamination risk.
From a cost perspective, one 1 bbl pitchable unit of liquid yeast (7 M cells mL⁻¹) is ~$80-100; repitching it ten times brings the effective cost to roughly $8-10 per batch. A fresh dry-yeast brick for the same volume is ~$50 each time-an expense that can add up if repitching is avoided due to contamination concerns. The per-unit price of liquid yeast also decreases noticeably at larger order sizes, further improving its economics.
It's worth sharing your MRS results with the dry-yeast supplier and requesting their batch microbial specifications to confirm whether the counts are within spec. If the data remain unsatisfactory, exploring liquid yeast as an alternative-given its aseptic production and potential cost savings with repitching-may be a practical next step.
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Kory Davis
QC and Propagation Specialist
The Brewing Science Institute
Woodland Park, Co
719-482-4895 ext. 3
Original Message:
Sent: 07-09-2025 12:46
From: Anonymous Member
Subject: LAB in Dry Yeast
This message was posted by a user wishing to remain anonymous
Hello,
Does anyone who uses ale or lager dry yeast and has a micro program notice issues with their dry yeast containing noticeable amounts of lactic acid bacteria? We've tested our yeast fresh out of the box by inoculating a MRS broth tube, and the subsequent results have all been positive for growth, specifically Lactobacillus. Samples from the fermenters usually plate negative until we get to the 3rd or 4th generation of the yeast, then we will see positives there as well. No issues with fermentation kinetics or sensory effects, but the presence is still concerning for us. Is this to be expected within the normal allowance of contaminants in the original dry yeast? Or should we follow up with our yeast supplier as a cause for concern?
Any and all experience & advice regarding this topic is appreciated. Thank you.