We had problem with french fries cooked at Perkins because they also do
their cheese curds in the same oil.   I mention this because it took
several trips and a year to figure that out.

>   Recently our daughter, who has a dairy allergy, had violent diarrhea
> immediately after eating some french fries, I suspect, at a chain
> restaurant (Friendly's).  Two weeks prior to that the same thing happened
> at another local restaurant after eating french fries.  So I put two and
> two together.  My question
> is this:  how widespread is this problem with french fries?  Are they
> often coated with whey or is it cassein, or what?  Should frozen french
> fries be avoided, generally?   Thanks for any information.