As an experienced homebrewer, one of the biggest mistakes I see that both new and experienced home brewers make in the process of making beer is failure to sanitize everything properly.
A good example of this is a couple of weeks ago I was making an easy beer recipe (an all grain Guinness clone from Austin Homebrew Supply). It was my 6th batch of beer made in as many weeks and I got sloppy. I still can’t pinpoint exactly where the infection came from but when I opened the fermenter to transfer it, the smell was horrendous.
I do know that it ended up being a late night, we were tired and mistakes were made.
The moral of the story is make sure you always have a sanitizing solution on hand and make sure that everything and I mean everything you use is sanitized after you boil your wort and the process of making beer will be much more rewarding.
The sanitizer I use for every brew day is One Step