I suppose they’re not really “hidden” sources of gluten, since these ingredients are right there on the label. You just need to realize that there is more to finding gluten in your food than avoiding the word “wheat”. It’s not as bad as trying to look out for secret non-vegan ingredients, but there are some things that can catch you if you’re not careful.
Kinds of Wheat
The first thing is that not all ingredients will list wheat as wheat. Depending on the labeling, products will sometimes chose to list the specific variety which can lead to confusion when on the look-out for gluten. You have to avoid durum, semolina, spelt, kamut, and bulgar as well. Ironically, you’re fine with buckwheat which isn’t actually a kind of wheat at all.
Don’t get caught up in the wheat though. There are a few other grains you need to avoid that also have gluten in them. Rye and barley are the two big ones that are common in foods. Triticale is a hybrid of rye and wheat, and also has gluten though you don’t see it too much.
Oats are often listed as a potential source of gluten but that’s not quite accurate, though worth noting. Oats themselves have no gluten. The problem is that most commercial sources of grains that supply oats also work with wheat, and oats are often contaminated with gluten from casual contact with wheat. Personally, I eat whole oats purchased from the Bulk Barn all the time with no problem but some people will react depending on their sensitivity levels and just how much wheat residue is in their oats. If you have issues, go for oats that are labeled as gluten-free to make sure they haven’t been handled in a wheat environment.
What about malt? This is one ingredient that often trips people up because it’s not immediately well-know that this is a grain product. It comes from sprouted-then-dried grains, most often barley but it can be made from wheat or other grains. Either way, it is considered a source of gluten and should be avoided.
So that’s the basics of looking for gluten ingredients. The trick is to remember to constantly read labels before you buy. Any kind of food product could have these, not just the obvious ones like baked goods, cereals or pasta. Many vegan meat substitutes are made with wheat gluten. Even Smarties candy has flour in it. Always read the labels.