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.