Having experienced some late blow in my wash curd cheese of recent..I was reading some of this information here and also reading the scientific literature..some of what is written here is not what the scientific literature says and i fear its mis-leading. I pulled some passages written by Alvenas 2015 for the Swedish University of Agricultural Sciences.
Page 8 Late gas defect is a typical condition of cheeses contaminated with propionic acid bacteria (PAB) or spore-forming Clostridia
Page 10 Clostridia spp. and Bacillus spp. are endospore-forming bacteria. (Willey et al. 2012)
Page 10 Endospore-forming bacteria and other spoilage organisms can be transferred from the cow to the milk if the udder is contaminated from dirt; either from soil, faeces or the bedding material (Heyndrickx et al. 2010)
Page 16 Pasteurization destroys the most heat-tolerant vegetative milk pathogens; Coxiella burnettii and Mycobacterium tuberculosis. Mold
spores are also destroyed, but not endospores (De Jong 2008; Ledenbach & Marschall 2010).
Page 17 Brine-salting is applied to most cheese varieties e.g. Gouda and Edam (Guinee 2007). It often takes a few weeks before salt has diffused from the rind to the interior which can pose a problem since proper and rapid salting inhibit blowing defects (Di Cagno & Gobbetti 2007
Page 20 Late blowing by Clostridia and PAB most often occur when salting is insufficient and pH is high (Featherstone 2008)
So it seems the endospores survive pasterization and most likely source is the milk handling pre-purchase but of course it may be introduced in the kitchen but less likely.
This all stands to reason in my case.
I have been making all types of cheeses over the last two years only of raw milk with no blow about 2 pounds each.
Recently in efforts to make larger wheels of cheese 7-8 pounds I have been adding in some pasteurized milk to my vat..raw is pricey.
Of my curd wash cheeses I've lost a few to blow.
OK I've done two things different.
New milk source and larger cheese. Milk source may not be an issue but the penetration of salt from the brine into the larger wheels happens to slow to prevent the endospores to start growing and producing gas. I'm going to look into longer brining time or maybe an additive like lysozyme. Additionally I think I know which milk source is the problem now that I've used 4 different 'brands'.