Obviously it is better to immediately boil the wort when it is freshest, giving any wild yeist or bacteria as little time as possible to grow and contaminate the product. It is also a well established practice to mash all of a recipe's different grains together simultaneously. These practices work wonderfully when brewing a single recipe at a time.

I am knocking around the idea of brewing multiple, smaller (2-3 gallon) batches simultaneously to allow more experimentation in my recipes. Beyond just revising the hopps/add-in timings, I want to play with the grain-bill, changing the quantities of each grain slightly for each batch. With extracts, that would be easy, but mashing each small batch seperately would be far too time consuming.

So here is what I have in mind...

Mashing each of my malts and adjuncts seperately in 5-10 gallon batches, then after sparging, cold-crash the resulting "single-malt" wort in a chest freezer. By recording the OG and volume of each seperate batch, I should be able to calculate a grain-weight to wort-volume ratio which I can use later, when translating my grain-bills from weight-based to volume-based. The mashing could all be done ahead of time, over time and in volume, so that on brew-day, I can start with a freezer full of different, nearly frozen, "single-malt" worts. From there, boiling up a bunch of small custom batches should be quick and easy; just mix in the appropriate ratios of each wort, and proceed to the boil.

So my questions "boil down to"...

Assuming that the freezer keeps the un-sterilized wort free of wild growth, what other negative-effects should I expect from the wort's time in cold-storage?

What time scale is safe for storing un-sterilized wort at cold-crash (but not frozen) levels? (a day, a few days, a week, or hopefully... weeks)

If any of you have tried something like this before, or if you've come up with another method of efficiently experimenting with small all-grain batches, please share your wisdom!

  • Sounds like you might need to experiment for yourself on this one. I've never heard/read anyone doing this and there might be good reasons not to. I'm guessing that as long as you're storing the wort under 37F you should be able to expect it to stay good for a couple weeks. I'd worry about oxygen degrading your malt as oxygen pretty much ruins all food stuffs. I'd still worry about contamination as that hour mash is the perfect environment for bacterial/yeast growth, and could start to grow even in 37F temps. This could give off flavors to your wort even despite boiling afterwards. Try it! Dec 10, 2014 at 1:26
  • 1
    Thanks! I intend to, as soon as I get past the gift-giving season. I need to give myself a bigger chest freezer. I've added to my plan slightly... I'm going to use bottled CO2 to evacuate any head space in my cold storage containers before I chill them. Just spraying into one hole in the cap while a second hole in the cap vents the original atmosphere. Then sealing both holes with soft wax or clay. I'll be starting the experiment by February and if our hosts at SE leave this question up till then, I will post my results back here as I find them. Dec 10, 2014 at 1:38
  • 1
    ...and if my soft wax seals break while in deep freeze or while I am slowly warming them back up, it will suggest that something might be growing in the wort. Just one more test for its sterility. Dec 10, 2014 at 1:41

2 Answers 2


The technique may work, and in theory, provided good process handling, shouldn't pose any issues. Something to consider though is that grain contains on it many organisms, including lactobacillus and enterobacter.

Without boiling neither of the organisms will be killed, and will also have been given time to grow in the wort during the mash. How well they survive / reproduce the near freezing temperatures is up for experimentation based on each wort I would imagine.

The biggest concern with these two microbes is that lactobacillus has the potential to sour your wort by producing lactic acid. This is actually one, albeit not ideal, method of creating a sour beer.

Enterobacter produces a different acid, butyric acid. This is commonly perceived as baby vomit, or fecal in the final product. If this organism is given the opportunity to entrench itself in your wort, your beer won't be very palatable.


My biggest concern would be botulism. If I'm not mistaken, unboiled wort is a very fertile breeding ground for that stuff. Even if "crash cooled in a freezer" I'd worry that too much of that bad stuff would stick around.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.