My celiac friends provided me with the proof I needed. But for the scientifically-minded brewer, here is a scientific explanation of what exactly happens with Brewer's Clarex/Clarity-Ferm (from "http://noglutennoproblem.blogspot.com/2010/10/product-review-estrella-damm-daura.html"). I am not a scientist, but I was able to understand this:
peterbronski [the author of the post] said...
Hi Otis... Thanks for your comment and caution. As you probably know, Brewers Clarex isn't the only way brewers reduce the amount of gluten in their beers - selecting low-protein varieties of barley, several steps of the brewing process, and prolonged cold storage (or other clarifying methods) all incrementally serve to reduce the total gluten present in a beer.
As far as peptides go, I think your concern is understandable, but - in my opinion - unfounded. I've interviewed several prominent Celiac researchers and brewing scientists on this topic, and have also read the peer-reviewed journal articles on the topic. Here are some things to keep in mind:
For starters, if you're interested in the citation for the original research mentioned in the LiveScience article link you provided, here it is:
"www.ncbi.nlm.nih.gov/pubmed/20650871"
Brewers Clarex is classified as a prolyl endoprotease, which basically means a "protein eating" enzyme that specifically targets the amino acid proline. The research you cite found that three peptides - each about 12 amino acids long - seem to cause many of the Celiac related problems. Scientists have previously sequenced barley hordein (for example, in this study in Biomedical and Life Sciences: "www.springerlink.com/content/a112273645778415/") and found that proline occurs more frequently than every 12 amino acids. It then stands to reason that barley hordein "digested" by proline-seeking Brewers Clarex would yield peptides too small to cause a Celiac reaction.
This seems to hold up in more recent studies. One study published in a 2006 issue of the American Journal of Physiology ("www.ncbi.nlm.nih.gov/pubmed/16690904") and a 2008 study published in the journal Gut ("www.ncbi.nlm.nih.gov/pubmed/17494108") both found that the prolyl endoprotease used in Brewers Clarex sufficiently degraded gluten to levels safe for Celiacs. They determined this not only by testing for full gluten, but also by looking for T cell immune reactivity to partial gluten peptides. In other words, the barley hordein peptides remaining after using Brewers Clarex are either too small or not the right type to cause a Celiac gluten response.