I looked on Wishbone's website b/c I had the same question and it states:
"Common ingredients that may contain gluten are rye, wheat, oats and barley, and noodles and pasta prepared with any of the previously mentioned grains. HVP, TVP, flavorings, are likely to contribute gluten as well, however, if they contain any gluten, the source would always be listed in the ingredient statements.
Since product formulations change from time to time, we do not have a printed list of products that identifies those products that contain specific allergens or gluten. The best advice we can give you is to check the ingredient list on the label. Ingredient allergens as defined by FDA: peanuts, tree nuts, soy, fish, seafood, wheat, eggs, and milk or dairy, as well as any ingredient that may contain gluten are always listed on the label. If gluten is present, it is clearly listed in plain language on the ingredient label (i.e., wheat flour, rye, barley, oats, and malt). Malt is a barley based ingredient.
We do not publish a list of gluten-free flavors. Therefore, we suggest reading all ingredient labels carefully. As always, if you cannot determine whether the product contains the ingredient in question, we recommend that you don't use it."
I discovered a Gluten Free Sake that is amazing. The name of the company is TY.KU - They make 4 different types of sake, all gluten free, contain no sulfites or tannens. They also make a citrus liquor and a soju (these are not gluten free). All their liquors contain no sugar; they all are made with real fruit juices and have half the calories of other liquors. All their sakes are top notch and should be served chilled. 76% of sake, specifically sake served hotis considered Futsu (very low grade).