Fish – How to prepare and grill blackened salmon

This is total nonsense: grass fed ribeye should absolutely not be tough. Toughness is, however, affected by the cow's breed, it's age, by how stressed it was when it was slaughtered, by ageing of the meat, and I'm sure a bunch of other variables too. Something made the meat tough, but it wasn't grass feeding - the combination of strong beefy flavour and toughness might suggest an old cow, for instance. Next time choose grass-fed beef raised by a different farmer.

Honestly, while your typical "combination" skewer looks more impressive, I find it's much better to grill them in separate skewers. One for beef, one for chicken, one for peppers, one for onions, etc. That way, you can cook each to their preferred temperature and not have to worry about the exact problem you're running into.

As far as cross contamination, you'll definitely minimize any risk grilling them as separate skewers, but since you didn't have chicken in the mix you should be relatively safe anyway. Once you sear the outside of the beef, you should be safe.

I picked this method up from an Alton Brown recommendation on a Good Eats episode (Scene 10), and found that I get considerably better results when I do it this way.