They’d mutate the s out of these Bacteria, in smart calculated ways. A basepair here, a gene there. When they hit a jack pot. They’d document the mutations, throw the engineered strain out and start blasting them with UV. Afterwards you just scan for the same mutations and voila, now it’s classical strain enhancement!

Same was done for yeast for all kinds of food applications.

There is something to be said for it because you never need antibiotic resistance for selection that way. But you also don’t really know what you are doing and you could edit the resistance genes out. Anyway, this was >20 years ago. Maybe they do it differently now.

It might also be interesting to use a dye to highlight dead cells.

It's also easy and cheap to run experiments too like mixing salt directly with the yeast and seeing it doesn't make a noticeable difference to breadmaking, yet the myths persist.