Yoghurt should be safe for a gluten free diet, but some brands to have the potential for gluten contamination.
Yoghurt is a food that can be considered safe for celiacs and those with a gluten allergy – most of the time. You do have to be careful though.
Some brands add thickeners to prevent the formation of whey. Gelatine is one method. Another is starch or even wheat flour.
In general, the fewer the ingredients, the better. I don’t think there is an excuse for adding wheat-based thickeners to yoghurt. I don’t think whey is a problem. Eat it, stir it into the yoghurt, or pour it off if it bothers you. Still, some people insist on natural consistency, and some manufacturers are only too happy to provide with substandard methods.
As with anywhere else in the food industry, this can lead to the addition of unexpected ingredients, such as adding starch or wheat to yoghurt.
Most brands that I’ve seen are gluten free, however I highly recommend that you always check the ingredients of yoghourt for starch of unspecified origin, wheat or gluten.
You can also make your own yoghurt, see the gluten free yogurt recipe elsewhere on this website. That way you get guaranteed gluten free yoghurt.
What brands of yoghurt have you noticed with gluten in it (and in what country)?