landhoney said:
mrk, I'd be happy to trust. So what you're saying is that once alcohol is produced it will kill the e.coli(or whatever)? That makes sense and seems reasonable. So, if your beer has over 1% ABV it has to be safe? Or something along those lines?
Not quite. Facultative anaerobes (like yeast, lacto, Staphylococcus, Salmonella, Listeria, etc) will survive in the presence of alcohol, as they produce it under anaerobic conditions (fermentation). But, their survival is a struggle, as the alcohol produced is toxic to their cells as it is to ours at certain concentrations. Unfortunately, those concentrations are greater than what you'll have in your beer. Similarly, the toxins that are produced by these microbes are more often the cause of the "toxicity" than the actual microbes themselves. So if you had, say,
Clostridium botulinum growing in your wort prior to pitching, and then you pitched your yeast/lacto/etc, the botulinum toxin would still be there even if the bacteria that produce it were dead/filtered/killed by increase in alcohol. They wouldn't be producing more toxin, but it wouldn't magically be going away.
What I'm saying is that under sanitary brewing conditions, there is no reason that any of those nasty microorganism should exist in the wort to begin with, and even if they did, they would be so outnumbered by the exponential growth of the "good" bacteria/yeast that the effect they might have on your beer would be negligible.
Lets put some numbers to it. Say you have 100 cells of Salmonella in your wort, prior to pitching 100 billion cells of Lactobacillus. And lets also say that they both have the same doubling rate of 1hr, and that you only have enough nutrient present to support 8 hours of fermentation, and that there are no hops present to inhibit the growth of bacteria. The growth would be such that:
Time, # Salmonella, # Lacto
1hr, 200 Cells, 2E9 cells
2hr, 400 Cells, 4E9 cells
3hr, 800 Cells, 8E9 cells
4hr, 1600 Cells, 1.6E10 cells
5hr, 3200 Cells, 3.2E10 cells
6hr, 6400 Cells, 6.4E10 cells
8hr, 25600 Cells, 2.56E11 cells
At 8hr, the nutrients would be used up, and the concentration of alcohol increases (inhibiting the bacteria that aren't capable of fermentation), both causing growth to level off. The number of lacto will have used the nutrients up at a much, much greater rate than that of Salmonella. Granted, as I said before, the toxins produced by the Salmonella may still be present in the wort (if they don't react with other compounds present and render themselves inert), however the amount is negligible as a result of their limited cell growth. This is one reason why it's so important to pitch a good, healthy growth.
If you were not sanitary in the brewhouse, and you did have a human pathogen present in a greater quantity...enough that it would actively compete with the pitching rate of your fermentation microbe, then yeah, you better believe that beer would be toxic. But we're sanitation nazis, so that's not an issue for us.
So to answer your father's question, because we use sanitary brewing equipment, and inoculate the media at a rate that outweighs any potential human pathogens by so many orders of magnitude, and (in hopped homebrews) because the presence of trans-humulone, (-)-humulone and colupulone are ionophores and thus inhibitory to bacteria, the environment is simply not favorable for the survival of human pathogens.
I hope that all made sense...sometimes I geek out a little bit much.
), I don't know...
