The first thing to establish is what kind of oil the restaurant uses. Always ask, and request to see the oil container if the wait staff give you a vague answer (i.e. “vegetable oil”) because some vegetable oil blends contain corn oil. Most places in Ontario these days use soy or canola oil, but I have recently run across restaurants that use corn oil, corn oil blends, sunflower oil, peanut oil, or olive oil exclusively. Often restaurants use different kinds of oil in their deep fryers than in their other dishes. Also, keep in mind that corn-based breading on someone else’s food may “contaminate” the deep-fryer oil even if it is itself a safe kind of oil.
If the restaurant staff are unsure of what kind of oil they use, but you still want to eat there, you can usually order a dish made with steamed food only, or have them cook your food in a separate pan using butter or olive oil.
Almost all fast food contains corn. The vast majority of burgers are held together with corn products as binders. Most breaded foods and pancakes and buns, breads, English muffins, pizza dough etc. contain corn flour and/or corn starch. McDonalds uses a corn oil blend in their deep-fryers. Salad dressings almost all contain corn derivatives as sweeteners or thickeners. Best to stick to restaurants that aren’t parts of chains. (Wendy’s does serve baked potatoes – but watch that they don’t give you corn-based margarine or dextrose-thickened sour cream on top!)
I’ve found that Asian restaurants use corn in the fewest dishes in general – but be aware that some brands of sushi rice are dusted with corn starch, and that mirin, even imported brands, is often sweetened with corn syrup. (Kokuho Rose is one brand of sushi rice that does not use corn starch). I have not yet found a corn-free tempura mix. Homemade teriyaki sauce is generally safe (it is made from soy sauce and sugar), though it always pays to ask about ingredients when ordering. Oyster sauce also tends to be thickened with corn. Although many Chinese restaurants use corn starch in their sauces, most of the ones in Toronto’s Chinatown seem to prefer potato starch or tapioca starch.
Authentic German and Eastern European restaurants and bakeries also tend not to use corn.
Any restaurant featuring food characteristic of the USA, Mexico, or Central or South America is likely to have corn in most dishes.
Take-out and delivery
Caution! Be alert to the possibility that take-out containers and plastic cutlery may be made from corn! I generally avoid food delivery. If there’s a problem with your order, you can’t send it back.