I'm reading Home Production of Quality Meats and Sausages and I'm not seeing how going from freezer to thawing in fridge to partially frozen (32F) would increase bacterial load in any meaningful way.
From the book:
"It can be seen that at 32° F (0° C) bacteria needs as much as 38 hours to divide in two. That also means that if our piece of meat had a certain amount of bacteriaon its surface, after 38 hours of lying in a refrigerator the amount of bacteria inthe same piece of meat will double. If we move this meat from the refrigerator toa room having a temperature of 80° F (26.5° C) the bacteria will double up everyhour (12 times faster). At 90° F (32° C) they will be dividing every 30 minutes. "
Inside a whole muscle is sterile. Bacteria are only on outer surface. AND IN AIR AND ON KNIFE AND HANDS AND GLOVES YOU TOUCH ANYTHING WITH. Bacteria can only start, and grow, on the outer surface. The instant you cut the meat in half, you almost double the surface area. This doubles the bacterial growth ability, AND because you thawed meat to cut, it also increases bacteria ability to grow.
By cubing a muscle, you increase bacterial risk, surface area, by about 100. By grinding, by 1000 or 10,000. And you ABSOLUTELY are introducing bacteria!
Unless you are working in a freezer or cold processing room, the surface mm of meat WILL WARM UP to above bacterial growth temps, and you WILL get a bacterial load onto the meat when chopping and grinding.
There are hurdles you can impose to bacterial growth, see all @indaswamp And @chopsaw said. If you are making ACTUAL salami, the highest risk product, then you need to use ALL the hurdles to inhibit bacteria.
If you're actually making something like summer sausage or bologna, where it is thawed for an hour, cured overnight in fridge, then rapidly heated to > 130f for pathogen lethality, then less care is needed. In this case, you can cube or grind stuff and freeze for use within a few weeks to avoid oxidation.
I have 3kg of ground pork in freezer from last week, gonna make that cotto salami being discussed recently. No issues, not a real salami. If I was making a dry cured aged salami, I would start whole muscle, cut with sterile knife, gloves, sterile board; grind with sterile grinder; innoculate and ferment immediately; then drop to 55f for drying ASAP.
Hope that is helpful! ;)
Oh, p.s. to your original question: the main reason some say not to grinf frozen meat is purely due to weak grinders. In fact, I absolutely recommend that your meat is still partially frozen, maybe 29-30f, before grinding! Soft enough to press and deforem with fingers, but not floppy thawed, still firm enough that grinder knives will bite and cut clean, not pull/tear/rip/deform like happens with meat >40f. Also, fat will grind without smearing into discrete particles that won't melt and will resist fat-out better. This is the MAIN REASON to get a bigger grinder, the ability to grind partially frozen meat.
