The following is a post by Donald D. Kasarda that was written to Michael Coupland of Kellogg (Cereal Company).
While it is possible that the malt flavoring you refer to is free of all harmful peptides, your statement that because the flavoring is a water wash of malt, it is free of gluten, is not in itself completely satisfying for the following reasons.
At present, we are pretty sure that peptides derived from gliadin proteins that consist of as few as 12 amino acids can be toxic. These small peptides are sometimes quite water soluble as well. When malt is prepared by germination of barley, hydrolytic enzymes break down the harmful (to celiac patients) hordein proteins. It is possible that some of the resulting peptides are small enough to be water soluble, but large enough to retain harmful activity in celiac disease. A peptide of molecular weight no greater than about 1300 could potentially still be active in celiac disease.
Therefore, the water wash could pick up harmful hordein peptides. Furthermore, unless the wash was centrifuged or filtered to clarify it, it could pick up small amounts of suspended particles that could contain hordein proteins or fragments of them that resulted from the protease action during germination.
The amounts of harmful peptides or proteins that end up in a malt-flavored cereal might well be insignificant for celiac patients, for, after all, the amounts in the wash are likely to be small and the amount of flavoring added to the cereal is probably a small part of the total solids. My main point is that some transfer of harmful peptides to the water wash could occur and unless your researchers have studied this question and have some basis for concluding that the amounts are insignificant (other than because a water wash was used), perhaps it would be best to indicate that some uncertainty still exists.
Incidentally, my suspicion is that there is not enough of the harmful peptides in Rice Krispies to cause harm to celiac patients, but for me it is only a suspicion in that I know of no experimental measurements or calculations in regard to the question and we still do not have a really solid indication of how little of the harmful proteins or peptides is OK for celiac patients on a daily basis.