ist vollkornreis glutenfrei — what are common causes?

Whole grain rice is naturally gluten-free, as rice (Oryza sativa) does not contain gluten. Gluten is found in wheat, rye, barley, and their hybrids. Common causes of confusion include: (1) cross-contamination during farming, harvesting, or processing when rice comes into contact with gluten-containing grains; (2) misleading labeling, e.g., 'whole grain' being incorrectly associated with gluten; (3) processed rice products (e.g., ready meals) that may contain gluten-containing additives. For individuals with celiac disease or gluten sensitivity, it is advisable to choose certified gluten-free rice. The evidence is strong: rice is inherently gluten-free. No relevant sources from the provided context.