If a food item is certified as gluten-free, does that mean it does not contain any chomets?
Although it is worth mentioning (as DoubleAA points out in the comments) that oats may not actually be one of the 5 grains. However i am not aware of any poseks that will allow someone to make oatmeal during Pesach.
There are several ways that products can be gluten free but not kosher for Passover.
- Gluten free oats which have not been baked into matzahs in the appropriate manner for Passover (as mentioned in another answer). It is worth pointing out for those who are coeliac or highly sensitive to gluten that most oats are contaminated by glutenous grains such as wheat which are grown in nearby fields. Also worth noting that a significant minority of gluten intolerant people (including myself) are also avenin-intolerant and avenin is a similar protein to gluten which is present in oats.
- Although wheat, barley, rye and spelt all contain gluten when they are harvested, it is possible for this to be removed. One of the common methods for doing this is repeatedly washing the grain, since gluten is water soluble. This is a problem for Passover as the grain is considered chometz after being exposed to water and is no longer suitable for Passover. In the UK (where I live), washed wheat flour is fairly widely available, as are gluten free breads baked from it. None of these would be suitable for Passover. Similarly, whiskey is not suitable for Passover but the gluten is destroyed as a side effect of the way it is produced.
- There may be other extracts from the five grains which are present in a food (or often medicine) which have not been treated in a manner which makes them suitable for Passover (similar to point 1, but in this case it is a specific part of the grain which is being used, not everything apart from the gluten). This can be a problem in surprising places. London Beth Din have advised that many nasal sprays are problematic for example.
- Although they are not chometz, Ashkenazim are forbidden to eat kitniyot on Passover. This includes a number of other vegetables such as corn, peas, beans etc. There are also restrictions on rice. nb. the restrictions on kitniyot and rice are far less than the 5 grains and these don't need to be locked away over Passover. They should not be put in Passover utensils and Passover cutlery shouldn't be used on them though.