In most cases, cheese you buy at the grocery store will be gluten-free. However, as with most types of food you'll consume while following a gluten-free diet, there are a few exceptions to this rule.
Cheese is made by combining milk, rennet (enzymes which curdle the milk), and bacteria, which ferments the milk to produce cheese. Plain cheese made with as few ingredients as possible will have undetectable levels of gluten in virtually every case.
Store-bought cheeses also may contain salt and sometimes preservatives; many also include extra ingredients to add flavor, such as herbs or spices.
Whenever you add extra ingredients, you increase the risk of gluten cross-contamination. However, in the vast majority of cases, these types of cheeses also will fall far below the currently-accepted "gluten-free" standard of 20 parts per million of gluten. You should check the label for gluten ingredients, and call the manufacturer if you're still in doubt.
There's one recent trend in gourmet cheese-making that's fairly worrisome: "beer-washed" cheeses are becoming popular, and companies are producing more of them. Beer is not gluten-free, of course, and any cheese produced or packaged on the same equipment as beer-washed cheese will be subject to cross-contamination.
Fortunately, there's usually an ample selection of different kinds of gourmet cheeses, even in smaller grocery stores, and so far I've avoided problems simply by steering clear of anything made by a company that also makes a beer-washed cheese.
Is Blue Cheese Gluten-Free?
There's some controversy over whether Roquefort or blue cheese is safe on a gluten-free diet, since the specific bacterial cultures used to create the cheese (known as Penicillium roqueforti) traditionally are grown on rye grains (rye is one of the three main gluten grains).
These days, few cheese makers use bacterial strains grown on rye to create their Roquefort or blue cheeses, but you'll need to ask in each case many use malt or wheat-based dextrose (both gluten-grain products) in place of rye.
Still, even if the manufacturer does use rye or another gluten grain product to grow the bacteria, the resulting cheese likely won't bother you unless you're particularly sensitive. In a 2009 study, the Canadian Celiac Association looked at gluten levels in several different varieties of blue cheese (all of which used gluten grain materials to grow the bacteria), and found them to be "undetectable," meaning any gluten present was at a concentration of less than 1 part per million.
If you can't find a source of safe blue cheese (or if you don't like blue cheese), you potentially can substitute another crumbly cheese, such as feta or goat cheese.
Gluten Cross-Contamination Possible in Cheese Packaging
It's unfortunately also possible for any cheese to have gluten cross-contamination introduced when it's handled or packaged.
Many stores especially more upscale supermarkets buy large wheels or blocks of cheeses, and then cut them up to sell in smaller quantities. If this cutting and repackaging takes place in the deli section where workers also make sandwiches, or in the bakery section where workers are using flour, the cheese can become cross-contaminated (I've been badly glutened by cheese repackaged in this way).
Therefore, it's best to stick with cheese that was packaged at the manufacturing facility. To tell the difference, the cheese that's repackaged at local stores usually is wrapped in basic plastic wrap that's held closed by a stick-on label, while cheese that's packaged at the manufacturing facility usually has a more substantial shrink-wrap-style plastic cover, sometimes with the label printed directly on it. If in doubt, of course, you should ask.
In addition, if you purchase cheese sliced at the deli counter, you risk that cheese being cross-contaminated in the slicing machine, since some sliced deli products contain gluten. Again, you're much better off purchasing cheese that was pre-sliced and then packaged at the manufacturer, although some people have reported success by asking store personnel to slice their cheese and other deli products in the early morning, after the equipment has been cleaned and before it's been used for gluten-containing deli products.
Is Shredded Cheese Gluten-Free?
There's another fairly persistent myth that shredded cheese may include a gluten ingredient as an anti-clumping agent.
Anti-clumping agents used by cheese manufacturers include powdered cellulose, calcium carbonate and potato starch. Of these, only powdered cellulose can be made from a gluten grain (wheat, usually), but in that case, the manufacturer should call out the wheat on the product's label.
In the U.S., both Kraft and Sargento two popular manufacturers of shredded cheese consider their shredded cheeses to be gluten-free to the generally accepted 20 parts per million standard. Sargento adds that the powdered cellulose it uses in its shredded cheese is not derived from any gluten grain.
Still, any additional production steps add to the risk of cross-contamination in the factory. Therefore, if you tend to react to very low levels of gluten, you may want to consider buying large pieces of cheese and shredding them yourself in a food processor or by hand.
Canadian Celiac Association. Blue Cheese in the Gluten-Free Diet - A Research Update. Celiac News, March 2009