Valid concern. Most places do not use it though. Once ya know what it smells like, you'll know to avoid it if your dewatering/filtering/conversion (bio-d) process does not remove it.

Mist washing is effective at removing it because the acid is soluble in water - but not oil. We have made 100's of gallons of B100 using boil out 'contaminated' VO. The BioPro 190 utilizes a triple mist wash, effectively removing any that may remain at that stage...

It can be tested for by placing WVO or B100 in a container, adding water and agitating. After the water separates, test it for Ph using litmus paper.

I actually ended up burning some of this in my F350 (2 tank VO conversion) shortly before changing injectors. (we normally set it aside for bio-d) The Swamps crew later showed me where this affected my injectors - although no 'pitting' was present, some parts were 'polished' indicating early stages of damage!! They also indicated that of the MANY VO injectors they've evaluated - boil out had caused the only real damage they saw.