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I believe this is perhaps only one question, but there are a few different situations, namely

  • to make a water/DME mixture for a starter, how long?
  • to prime with a sugar water mixture, how long?
  • to prime with gyle (4-6 week old wort from the boil), how long?

I ask because I had been boiling for only a short period, a couple of minutes. I came across an EPA recommendation for 1 minute, or 3 minutes for high altitude (I am at ~6500ft where water boils at 200F), but also found some brewing sites recommending between 15 and 30 minutes. What I haven't found is why the times are different. What I suspect is that common bacteria are killed at 1-2 minutes, and perhaps more of the bacteria brewers are concerned with might take more, but I haven't found anything to support this. A friend pointed out there are some spores that survive 5432F rocket exhaust, so I understand you are never going to be completely sterile, but would like to understand why the guidelines cover a range and be able to make an informed decision about how long to boil.

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wow. rocket exhaust! :) –  mdma Feb 26 at 21:55
Responding as a comment, because this is not an authoritative answer: (1) for starters, I boil 5 minutes and let cool ambiently because I want the starter wort to be sterile enough for yeast to overtake unwanted microorganisms - 10 minutes above 180°F is enough to pasteurize the starter, I believe; and (2) for priming solution (sugar or gyle), this is going into a low pH, high-alcohol environment, so I wouldn't worry too much - again pasteurizing it should be more than enough. –  Chino Brews Feb 26 at 22:54

3 Answers 3

I think the factor isn't that you want sterile wort, but sanitized wort. You may not get sterile wort from boiling, but that isn't a problem. The wort is surrounded by barely sanitary air, so it's going to be contaminated to some degree from the get go.

The key point is that the massive yeast population (>100bn cells for a 5 gallon batch) scavenge dissolved oxygen from the wort, drive off headspace oxygen with carbon dioxide, and reduce the wort to below 4.5pH, all of which make for an unthriving enviroment for all common bacterial contaminants.

So, a short boil period, really even just patuerization over 170°F/76°C is sufficient for short term storage.

For long term storage of wort, there are no yeast, so it must be sterile. Then you have to heat under pressure to 240°F for 15 minutes to ensure all bacteria and spores are destroyed, as per regular food canning guidelines.

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I don't think I can reach 240F. Once my wort begins boiling, even at a raging boil, it never really gets any hotter than about 200F. I have gotten candy sugar hotter, like syrup, which I've gotten >>270. –  Wyrmwood Feb 26 at 23:03
What is the "breaking point" for an anaerobic bacteria such as Lactobacillus delbrueckii? Carbon Dioxide will not stop it from fermenting, and it's known for it's ability to ferment lactic acid. What is its pH, IBU & ABV tolerance? –  Scott Feb 27 at 6:34
I should have clarified - you can only get wort to 240F in a pressure canner. –  mdma Feb 27 at 6:50
Does it benefit to boil for 20 minutes (over say 3 minutes) when not under pressure? –  Wyrmwood Feb 28 at 2:40
I doubt it - the idea is that the wort does not need to be sterile, just sanitary when pitching yeast. The carboy, surrounding air etc.. are only sanitary, not sterile, so making the wort sterile seems to be of little point. –  mdma Feb 28 at 12:06

10 min boil extra 1/2 cups water, what you may lose during that time. DME/Prime Sugar. Why risk losing your beer over saving few minutes.

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I hate answer my own question, but I believe I have cobbled together at least some of the information I am looking for.

As mdma pointed out, you need a pressure cooker or an autoclave (performed correctly) to sterilize.

For safe drinking water, "common" bacteria are killed in 1 minute (or 3 minutes at altitude).

The only other reference I could find was that "most" bacteria are killed by a 15 minute boil. This isn't referenced in the wiki article and the comment is terse, so I don't think this is definitive... but I do think it's notable that it mentions "most".

I think this last statement kind of lends credence to user6042's comment about the risk. Being at high altitude, I would probably adjust that to 20 minutes.

Thanks for all the help!

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