Infections

[hatless]

I tried and abandoned brewing a few years ago because I had a couple of brews that got infected - at least, tasted so nasty you didn't want to do more than sip them experimentally. Recently I've started again, been very careful with sterilisation, have one brew in a pressure barrel and another fermenting away right now, and they smell lovely and sweet. So far so good, but I have a few lingering questions.

The thinking seems to be that the risk of infection is greatest at the very beginning. My Cooper's kit told me the ideal temperature for pitching the yeast but stressed that, as long as it's not so hot it's going to kill the yeast, any temperature will do; it's more important to get the yeast in quickly than waste another few hours letting it cool.

I remember the books I had years ago telling me that once it's vigorously fermenting, yeast can outcompete anything else, and that all the CO2 protects it.

Also, I've come across comments suggesting that it's the FV that can cause contamination.

So, what exactly is contamination? Are there particular 'bugs' that get in? People mention both bacteria and wild yeasts - can you tell them apart? Aren't they around in the air everywhere anyway? Is it just at risk for a few hours before the yeast gets going?

Is a brew safe when its foaming away? Some people use airlocks, but most seem not to. Why is this safe? Another thread talks about leaving the beer in the FV, or in a secondary FV for a week or more after fermentation has died down. More than three weeks risks off flavours from dead yeast, but not, apparently from infection.

Home brewed beer is 'live.' Does that mean that it will almost certainly have some wild yeasts present, and some bacteria too, but usually not in quantities sufficient to spoil the flavour?

Exposure to air tends to make wine and beer taste sour the next morning, if a bottle is left opened overnight. Is this oxidation? Why isn't it a problem in the FV?

[Garth]

in the fv there is usually a thin blanket of CO2 given off by the fermenting the wort which is protecting the brew from oxidation

as the yeast slowly comes to a stop there is more risk of spoiling as there is less CO2 produced and less protection

[hatless]

Interesting what you say about sugar, Chris. I never thought it would make any difference, but I'm currently fermenting a kit where I used DME instead of sugar, and it actually smells very little indeed.