Is cornstarch gluten free?
Cornstarch, or corn starch or cornflour, is a starch that comes from corn. It is often used for thickening soups and sauces and can be used as a substitute for arrowroot at a 1:1 ratio. Like the corn it comes from, it is naturally gluten free. Likewise, if you are sensitive to corn, you may want to be wary of cornstarch. Also, if blood glucose levels concern you, cornstarch makes them rise faster than sugar.
Fun fact: Cornstarch was used mostly for starching laundry, rather than for cooking, up through the mid 19th century. Also, it makes a non-Newtonian fluid when mixed with water.
If you are among the people who are affected by cross-contamination, you will want to make sure that the cornstarch you buy has been processed in a facility that protects against cross-contamination. Unfortunately, not all brands are.
Gluten free cornstarch products
Clabber Girl (and Hearth Club) tests for gluten at 20ppm for their cornstarch.
Argo (and Kingsford’s) claims that their cornstarch is gluten free. They only produce cornstarch and baking powder, so cross-contamination is unlikely.
Some brands which are not considered gluten free are Cream, Hodgson Mill, Rapunzel, and Rumford.