Can you post a picture of the plant ?
It seems to me as if you are sun drying them.
Once the tomato is ripe there no point keeping it on the vine under hot sun.

Lack of water, I would think. In the soil or by some lack of uptake.

So it's only the beefsteak plants that are affected and the others, the cherries, are fine? if so it doesn't sound like lack of water to me.

What was the source of the affected plants,purchased or grown from seed by you, and what gardening zone are you in and what has the weather been like?

I have something in mind, but need you to confirm that its only the the beefsteak ones affected and what the source of those plants was.

Carolyn

Yes, only the ~80 Beefsteaks are affected. The ~30 Large Red Cherries and ~30 Sweet 100's are all fine.

The three varieties were sourced from different companies but all were grown by us from seed. First indoors and then on our front porch, before being put in the ground 6-8 weeks ago.

Thanks

What zone are you? It maybe too hot and not getting enough water that is what it looks like, Beefsteak will burn and dry out faster then cherry varieties.

Zone 6 / 7 mid TN. Is beefsteak more water-sensitive than other non-cherry tomatoes?