Biofilms - the reason you should care about protein stains.

Transient

This summary of the paper 'Adhesion and biofilm production by wine isolates of Brettanomyces bruxellensis' from Viticulture and Enology from UC Davis outlines some interesting points about the formation of biofilms and how they can lead to Brettanomyces infestations.  

The main points to take away from the summary is that in order to suitably control for an outbreak of Brett, it is important to have a reliable cleaning regime in place.  This is especially so in relation to protein stains and biofilms, as they are a key breeding ground for Brett isolates.  If your cleaning agent doesn't have the requisite power to bust through these heavy stains and biofilms, then you are setting your winery up for a potential disaster.

Another key point, is that simply sanitising without thoroughly cleaning is not sufficient to break down biofilm and thus avert a potential Brett infestation. 

You can find the summary here, it's well worth a read.