The Question: Is all vinegar gluten-free?
The Answer: MOST vinegar is, but SOME DO CONTAIN GLUTEN.
Gluten-free vinegar is a touchy topic for many experts in the gluten-free community who consider distilled vinegar to be safe because the vinegar distillation process breaks down and eliminates the gluten protein fragments.  While other experts question the safety of anything that begins as a gluten grain referring to testing technology for gluten, that does not always pick up smaller fragments of the protein that may cause people to react.
Then you have people diagnosed with celiac disease and non-celiac gluten sensitivity who suffer through a gluten grain reaction when they ingest vinegar derived from gluten grains, regardless of what either group of experts says.
The clear-cut answer you’re looking for might be trial and error.
While some experts differ in their opinions of whether distilled vinegar made from gluten grains (wheat being the common source of white vinegar) is safe for everyone eating a gluten-free diet, the ultimate answer lies in what works for each individual.
Few people who are very sensitive to trace gluten will react to all types of vinegar, including the kinds listed as safe. If that is the case, the cause could be gluten-cross contamination in manufacturing the product or possibly trace gluten contamination in the ingredients used to make the vinegar. The root cause may also be that the person is reacting to something else in the vinegar, and that gluten is not the problem at all.
The vast majority of people eating a gluten-free diet will not need to worry about vinegar in the “Usually Safe” category at all. But if you cannot seem to find a vinegar that doesn’t cause you to react, you may want to consider making vinegar at home.
USUALLY SAFE gluten-free vinegar:
• Apple Cider Vinegar
• Most Distilled Vinegar, (grain vinegar, spirit vinegar, white vinegar)
• Balsamic Vinegar
• Cane Vinegar
• Wine Vinegar
• Grape Vinegar
Plain distilled kinds of vinegar are gluten-free even when made with gluten-containing grains when gluten is removed during the distillation process rendering the final product gluten-free.
ALWAYS AVOID malt and rye vinegar:
MALT VINEGAR is most times made from barley, and it may also be produced from rye, called Rye Vinegar, which is NOT GLUTEN-FREE. Malt or rye vinegar is fermented and is not safe for people with celiac disease. These vinigars are not distilled vinegar, and they do contain gluten.
Other kinds of vinegar that may contain gluten.
Read the ingredient labels carefully.
Flavored Vinegar – While many flavored vinegars are safe, some may contain malt or wheat (As an example, Heinz Tarragon Vinegar contains barley). Please read the ingredient labels carefully.
Asian Rice Vinegar – May contain wheat; you will find it listed on the ingredient label.
Read more, including a breakdown of the gluten-free status of vinegar.