Eating in the 15th century

If I were magically transported back to, say, the 15th century; a time when merchants adulterated food like crazy and hygiene wasn’t all it could be; would I be safer eating kosher food?

Possibly a bit safer, but not much. Kosher food would be less likely to be adulterated, at least to the extent that something represented as “cow” definitely would not have been extended with pork. You’d also be at a somewhat lower risk of cross-contamination between meat products and dairy products. You might also benefit indirectly from the food preparers’ ritual handwashing.

However, as you point out, hygiene wasn’t great at the time, in part because a lot of what we know now simply wasn’t understood then. Meat products, kosher or not, would have been at high risk of contamination from skin and intestinal bacteria during the butchering process. Dairy products would have been at risk of contamination from insufficiently cleaned buckets, cheesemaking equipment, etc. Modern tools such as refrigeration (not to mention window screens and chemical sanitizers) would have been nonexistent.

I wouldn’t eat in the 15th century if I were you.

What would make you think most food was adulterated? Chances are most of the food you would be buying would be fresh vegetables and cuts of meat- not much room to mess around there. Grain might be a problem, but even then your risk is likely simply that it’d be cut with lower-quality grains. There were not tons of chemicals and manufactured products to be cutting stuff with.

Likewise, most cultures develop techniques for maintaining basic hygiene even without a knowledge of germ theory. Chances are you would never eat stuff like raw vegetables or rare meat. Just make sure all of the food you eat is freshly cooked, peel your fruit and boil your water and you will not have too many problems.

Millions of people today live without basic sanitation. It does cause problems, especially for children. But most of those problems are because the indigenous food safety systems do not work with increased population density (i.e. shitting behind a bush works in your 100 person village fine, but causes all kinds of illness when it happens in cities), not because they don’t work at all.

Adulteration came much later, when people learned how to adulterate. It’s not like there were a lot of chemical substitutes around. I suppose you could put chalk in bread, but breadmakers do it now.*

Most people raised their own food. Foods were most often some form of grain (meat was expensive and most vegetables seasonal). Root vegetables were common, since they kept well, and cabbage was also popular (since it was easy to grow and could be turned into sauerkraut or the equivalent). Most cooking consisted of boiling things until they were done (since that was the easiest way to cook on a hearth), which helped reduce food poisoning.

Bread was easily available, but there were usually regulations about the size of a loaf and other quality controls.

*To increase calcium.

I think it would be a terrible choice for your personal health to out yourself as a likely Jew during the Spanish Inquisition.