Cross-contamination happens whenever gluten (or another unwanted ingredient) is transported from one food item to another (usually unintentionally).
While a restaurant dish or packaged food may be labeled “gluten-free”, this may not always be the case in reality. Studies with Nima show that one out of three gluten-free restaurant foods in the US actually contain traces of gluten – read more here. Labelled gluten-free pizza and pasta most often tested positive for gluten at restaurants. This can be due to staff miscommunication, mislabeling, and cross contamination.
The tiniest crumb of gluten can compromise an otherwise gluten-free food, so great care must be taken to avoid cross-contamination between gluten-containing and gluten-free foods. Nima can accurately detect a fraction of a crumb of peanut and gluten in a sample of food, and can help aid your diligence by taking the first bite. Read about our validation and accuracy here.
These are scenarios where we have seen the most examples of cross:
Gluten-free pasta may have been boiled in water that was already used to boil regular, gluten-containing pasta. Or, the drainer may have been used to drain regular pasta. Ask the kitchen to use a new pot, drainer, and water to avoid cross contact with previously made pastas.
A server notices a gluten-free burger was made with a regular, non-gluten-free bun. Instead of replacing the entire dish, the server places the same burger and toppings onto a new gluten-free bun. Removing the bun doesn’t make it gluten free, as crumbs and other tiny amounts of gluten from the original bun stick to the patty/cheese/everything else on the plate.
The same fryers are used for onion rings (battered in gluten-containing flour) and gluten-free french-fries. The oil carries gluten from the onion ring batter to the french-fries, making them very much not gluten-free.
The same knife is used to slice a loaf of wheat-bread and a loaf of gluten-free bread, crumbs from the wheat-bread are transported onto the gluten-free bread and compromise its gluten-free-ness.
A GF pizza cooked in an oven with gluten containing pizza will likely have cross contamination. Food preparers should also change gloves when handling toppings for the GF pizza. Ask what special instructions are to cook the GF pizzas and request gloves to be changed for toppings.