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Contamination from one batch to the next

This subject keeps coming up, and it seems to me that people are freaking out unnecessarily. So I thought I’d start a thread on the subject. As far as I can see, there are three potential situations that people might worry about:

  1. A strong flavor from a previous batch carrying over to the next batch.

  2. A non-yeast organism present that carries over (could be from intentionally soured beer or from infection)

  3. One strain of yeast carrying over and creating non-desired flavors in the new beer.

Is there anything I missed?

Taking the third point first (a brewer recently posted a question about this with regards to saison yeast), I think that is a total non-issue. With proper cleaning and sanitation, the chance of some small remnant population of yeast surviving to the next brew is very slim. And if any does, it will be so out-competed by the healthy, abundant population of pitched yeast that it won’t be an issue. This is one reason you never hear about pitching more than one yeast strain to increase the complexity of the fermentation esters: it doesn’t work. One strain will dominate and not let the other strain contribute at a detectable level.

The second situation (non-yeast organism) is more of a concern, but still not very much of one. Proper cleaning and sanitation will be quite effective in metal, plastic or ceramic (including glass) equipment, unless there are crevices that the sanitizer can’t get to, such as occurs on hose and valve fittings. I’ve personally had zero contamination issues when using scratched plastic fermentation buckets after infections (which were directly traceable to fresh fruit additions). The sanitizer is pretty good at killing those organisms. However, if some do survive, and they eat something different than the pitched yeast, they will have the potential to thrive and not be checked by the healthy yeast.

The first situation is a very real concern, and you just have to make a batch of root beer in your beer equipment to know how bad it could be. It depends on the specific flavor compounds and equipment characteristics, but especially with plastic and rubber parts you should keep this in mind.

Never had a problem with any of these. I use PBW on equipment in between batches and it seems to oxidize away most carryover aromas/flavors.

I do occasionally worry about carryover from starters. If the starter sort is dark or particularly hoppy/aromatic (I use extra wort from batches) I make sure to cold crash.

I never had a problem with #1 or #3. I have had many many problems with #2. Lots of unintentially soured beers and contaminated batches. These were due to plastic buckets – didn’t matter if they were scratched or unscratched – infected either way. Now I use only glass fermenters and I expect I’ll never have an issue again.

The root beer example is a good one of how #1 could apply in certain situations. But as long as you are making “normal” beers, it really shouldn’t be a problem. Again… with glass, you completely eliminate the potential.

I’ve only had a problem with #2. It was from the bottling bucket. I bottled half a batch and kegged the rest. The kegged portion was fine. I haven’t bottled since, so I can’t say yet whether I’ve eradicated the problem.

I have been thinking about kegging a batch that contains Brett and maybe a Berliner Weisse. If I do keg them, I might dedicate a faucet to buggy beers just to be on the safe side. With six faucets I can afford to take the extra precaution.

I’ve had a couple problems with # 2. I had two batches made from the same jar of harvest yeast that was about 2 month old, both had a funky type flavor and wouldn’t clear. I got rid of all my harvest yeast and did a real thorough job cleaning and sanitizing all of my equipment. I Made 4 beers with no problems but now I have 2 10 gallon batches that are showing the same signs(pitched yeast from one to the next). So I not sure what has happen this time but I’m pretty pissed both batches were higher gravity and hoppy so it was an expensive loss.

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