Yes sauces and juices, if cooked at too high a temperature will foam. Usually it just stirs back into the liquid. Otherwise you can skim it.

What particular tomato product were you cooking?

Dave

I'm just making a standard tomato sauce. I lowered the temp, and most of it is gone now. I'll skim the rest.

After I posted this question, someone installed a new operating system on my computer (DS), so I just got access back, or I would have responded sooner.