I'm going to give you my serious answer to your question, about when you should stop WORRYING about infection. The answer is you should never WORRY about infection, or really anything else about this hobby. Because that is what it is, it is a hobby after all, and a really hard one to screw up.
Now it doesn't mean you ignore proper sanitation practices, and cut corners, or that you don't be careful about things, it is just that you stop thinking of your beer as a weak newborn baby.
It may appear that there's a ton of infection threads, BUT if you actually read the content of the threads, and not just the title, you will realize that
there's not a lot of actual infections, just a bunch of scared new brewers who don't realize how ugly fermentation can actually be.
Just like you, I bet, they think that their beer is a lot weaker than it truly is. Just the opposite, it is really really hard to get an infection.
And infections RARELY happen to the new brewers who are so paranoid that they think the mere looking at their fermenters will induce an infection.
Most of the time on here the beer in question is not infected. It's just a nervous new brewer, who THINKS something is wrong when in reality they are just unused to the ugliness that beer making often is.
It creates sort of like the hypochodria that med students often get when they start learning about illness, they start to "feel" it in themselves.
There is a lot of info here on "infections"
https://www.homebrewtalk.com/f39/has-anyone-ever-messed-up-batch-96644/
This is one of the best posts on the subject....
If you pitch enough viable, healthy yeast to do their job, it's hard to contaminate your brew to the point it isn't drinkable. Trust me, I've had an infection in my brewery, and I had to work really hard to get it!
In my case, it was on the fourth generation of re-using yeast which I had not washed properly (I was still a n00b back then). Every time you reuse yeast you are growing the level of contamination by 100-1000x, so I learned the hard way you have to be very careful going beyond 1 or 2 re-uses of yeast.
BUT A new brewer following sanitary procedures using new equipment is very unlikely to have ruined beer. The worst thing that may happen is your beer will go sour after 4-6 months of room temperature storage. I doubt your beer will last that long.
You'll find that since beer has been made for millenia even before anyone understood germ theory, that even just the basic fact that we have indoor water, clean our living spaces and ourselves regularly and have closed waste systems, and a roof over our heads, that we are lightyears ahead of our ancestor brewers.
And despite the doomsayers who say that ancient beer was consumed young because it would go bad, they forget the fact that most of those beers were usually HOPLESS, and that the biggest reason hops were placed in beers was for it's antisceptic/preservative function.
So even if the beer had to be consumed young, it still must have tasted good enough to those folks most of the time to
survive culturally for 4,000 years, and not go the way of pepsi clear or new coke. I'm sure even a few hundred or thousands of years ago, people were discerning enough to know if something tasted good or nasty...
Go take a look at my photo walkthrough of Labatt's first "pioneer" brewery from the 1840's
https://www.homebrewtalk.com/f85/labatt-pioneer-brewery-128740/
Wood fermenters, open cooling pans, open doors, cracks in the logs and beams letting air in, and not one bottle of starsan in sight.
The way I figure even just having some soap and water, basic 21st century hygiene, and a basic understanding of germ theory trumps how it was done from Gilgamesh's time through Louis Pasteure's....
In most places we don't have to even worry about boiling our water before drinking it.
Best advice I have for new brewers,
If you brew from fear, you won't make great beer!
You might make drinkable beer, or you might make crap...but until your realize that your beer is much hardier than you think it is, you will find that this is much more enjoyable of a hobby.
But infection worry, It is NOT something we have to freak out about, like new brewers do...It's just something to be AWARE of and keep an eye out.
But it's kinda like when you have a brand new car, you park at the far end of the lot away from everyone else, you are paranoid about getting every little scratch on it...Then you are backing out of the garage and take off a mirror, or get a ding on the bumper, then you no-longer stress out about it, because you've popped the cars cherry...If you do pick up a bug, you just treat it and move on.
And the reason I have collected THESE stories is to counter the fear and fear mongering that often happens.
So rather than looking for infections under every bed or in every brew closet, focussing from fear on the negative, I think it's better to look at examples of just how hard it is to screw up our beer, how no matter what we can do to screw up, it still manages to turn out fine.
https://www.homebrewtalk.com/f39/wh...where-your-beer-still-turned-out-great-96780/
And there is a cushion of co2 protecting your beer, so unless you or a bird take a crap in your fermenter, opening it up to take hydrometer readings will not lead you to automatically have infections...
Just relax about infections, and enjoy brewing.
