The dietitian Tricia Thompson, who did the research that measured significant wheat contamination in oat brands including McCann's, recently collaborated with other gluten-aware dietitians in addressing concerns about the possibility of gluten in vinegar.
Their findings—summarized in Tricia's blog post, "Vinegar: When Is It Gluten-Free?"—were generally consistent with research published in Gluten-Free Living suggesting that the vast majority of common vinegars are gluten-free.
The main points:
The contributors to this recent statement are all dietitians notable for their expertise concerning celiac disease: In addition to Thompson, they include Cynthia Kupper of GIG, Melinda Dennis of Boston's Celiac Center at Beth Israel Deaconess Medical Center (CCBIDMC), author Mary K. Sharrett of Nationwide Children's Hospital of Ohio (NCHO), Anne Lee (formerly of the Celiac Disease Center at Columbia University--CDCCU), and Pam Cureton of the University of Maryland Center for Celiac Research (UMCCR).
Distilled vinegar is gluten-free, no matter what the source material may be, because (the ancient and medically reliable process of) distillation separates all proteins from the final product. "Vinegar" simply listed as an ingredient can be considered safe—made from apples. Check non-distilled and flavored vinegars. The most common non-distilled vinegar that would be of concern is malt vinegar; some Asian black rice vinegars might also merit concern.