I know that sanitization is one of the most fundamental parts of making a beer and I myself wasted two batches already for not being diligent as I should. So, what are the steps / moments when you are making a beer that are the most critical for contamination to happen? Tks!
Just before you add yeast.
- Your wort will not be heated again
- Wort is full of nutrients, fullest it was or will be
- Temperature is optimal for microbiological growth
- No competition with other microbes
- No alcohol yet
Everything that has contact with wort before yeast kick in are most crucial.
For full bodied, weak beers and ales, bottling is in my opinion second "best". Bacteria, mold, wild yeast can metabolize sugars ale yeast can not. And may be resistant enough to survive alcohol content you have. For things like Old Ale, that are expected to get some sour, it's all right. For milk stout, you can make bottle grenades.
Racking to secondary basically have the same issues.
Interesting stage is mash. Of course, nothing should survive later boil, but if you forget about your mash tun, or wet crush and then delay mash for some reason, you can get sourness. Lactic acid bacteria are pretty common. You can pretty much assume you have small scale contamination from the beginning. Usually you just don't give it a time to actually do anything.