Question: Is all vinegar gluten-free?
Answer: MOST vinegar is, but SOME DO CONTAIN GLUTEN.
Right up there at the top list of touchy subjects by experts in the gluten-free community is a discussion about if vinegar is truly gluten-free.
On one side of the aisle, many experts consider distilled vinegar safe because the vinegar distillation process breaks down and eliminates the gluten protein fragments. 
Still, on the opposing side, other experts question the safety of anything that begins as a gluten grain. These experts are referring to testing technology for gluten that does not always pick up smaller protein fragments that may cause people to react.
Lastly, 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.
When deciding for yourself, the clear-cut answer may 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 sensitive to trace gluten will react to all types of vinegar, including those listed as safe. If that is the case, the cause could be gluten-cross contamination in manufacturing the product. Surely it could also possibly be trace gluten contamination in the ingredients used to make the vinegar. Or, to that end, the root cause may also be that the person is reacting to something else in the vinegar and that gluten is not the problem.
Granted, most people eating a gluten-free diet will not need to worry about vinegar in the “Usually Safe” category. But if you cannot find a vinegar that doesn’t cause you to react, you may want to consider making vinegar at home.
The USUALLY SAFE gluten-free vinegar list:
- 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 often made from barley and may also be produced from rye, called Rye Vinegar, which is NOT GLUTEN-FREE.
Both malt and rye vinegar is fermented and is not safe for people with celiac disease. These kinds of vinegar are not distilled vinegar, and they do contain gluten.
Other kinds of vinegar that may contain gluten.
Always read the ingredient labels carefully.
Flavored Vinegar – While many flavored kinds of vinegar are safe, some flavors may contain malt or wheat (for example, Heinz Tarragon Vinegar contains barley). So, please always read the ingredient labels carefully.
Asian Rice Vinegar – This vinegar may also contain wheat. If so, you will find it listed on the ingredient label.
Read more, including a breakdown of the gluten-free status of vinegar. 
 Celiac Disease Foundation. Sources of Gluten.
 GlutenFreeDietitian.com, a site maintained by celiac disease and gluten-free diet expert Tricia Thompson, MS, RD.