Please explain why people don't get infections in their beer until they move to secondary and expose too much of the surface to air. Infections in primary where there is a good cover in CO2 are incredibly rare and need some poor sanitation to get a start. The sources I found said that these bacteria cannot reproduce in beer without oxygen. They may be anaerobic and able to reproduce in other liquids but not in beer.
People do get contaminations in primary.
The organisms I pointed out are all known to contaminate beer and all grow in beer anaerobically. Oxygen is not required for their growth.
From personal experience I can say it's super easy to sour a beer by adding Lactobacillus to an unhopped beer during active fermentation in primary, when it's 100% anerobic. Souring occurs in a matter of days.
After you transfer your microbial growth medium (wort) into your first fermenter you aerate or oxygenate, right? That's way more oxygen than will ever be in beer transferred to a secondary vessel.
The reason for the
perception that contamination occurs in secondary is that a pellicle forms in the presence of oxygen. The pellicle is just a visual indicator that there is a contamination. The wild microbes certainly could have been there before transferring, and probably were. They just weren't noticed.
Furthermore, contaminations develop over time from low starting cell counts, so a longer fermentation just gives the wild microbes more time to develop.
Lastly, new brewers often use secondaries and their cleaning and sanitation practices may not be 100%. This is a confounding variable. Many long-time brewers will emphatically tell you that they always use secondary and don't have issues with contamination.
Using a secondary vessel obviously increases risk of picking up a contaminant vs not doing so, but is clearly not the most common contamination vector because there's no greater risk involved than there was when putting the wort into the first vessel (and aerating!).
Hope this makes sense.
