Sounds like it should be simple, but it can actually be quite tricky.
There are some relatively new, and very clever, ways that wheat gluten is being applied in making processed foods “better”. Just to illustrate my point: one interesting development has been to stripe a coating made from wheat gluten protein onto raw meat patties. When they are cooked on a flat griddle, they develop dark brown stripes that make it look like they were cooked on a charcoal grille.
It may taste great, look appealing, but it is NOT SAFE for people avoiding gluten to eat this food. We will refer to foods as being safe, or not safe, to indicate the risk of gluten presence. We refer to it this way since many who are avoiding gluten suffer significant discomfort (severe pain, even) when they accidentally consume wheat gluten. The same effect is caused by barley gluten and rye gluten, but we will generally call it all gluten.
Most (all?) other seeds contain storage proteins, and some are said to contain gluten protein, but, unless a specific seed source for a gluten ingredient is specified, it is most prudent to consider all “gluten” as being derived from wheat.
Some people say they can tolerate small amounts of gluten, so they are not as worried about avoiding extremely tiny quantities such as might happen with cross-contamination in a factory that makes products using wheat flour, and uses the same equipment to make a non-wheat-containing product. Some people will react to foods containing less than 10 parts per million of gluten protein, and that is the lower limit for the sensitivity of the most sensitive gluten protein laboratory test, the ELISA. So we will treat “No Gluten” to mean that literally – a zero tolerance – for any at all.
With that as a preface, we could suggest that an (almost) absolutely certain way to completely avoid gluten from wheat , barley and rye is to avoid all “processed” foods. This would even keep you out of the freezer section of your grocery store. (Some frozen uncooked meats have been coated with a frost-burn preventative coating that contains gluten protein.)
Safe animal source foods include all butchered meats that are store-packaged by your local butcher. Also safe would be large cuts of meat that are sealed in heavy plastic shrink packages at the slaughterhouse, intending to be used by restaurants or to be further butchered and repackaged at a store meat department. Generally all fresh wild-caught fish, shellfish, crabs, chicken, beef, pork, lamb, and like items will be safe.
Safe plant source foods include all the fresh produce that arrives at the store in bulk and is presented fresh in produce display counters at a grocery store. This can even include items such as tomatoes, and various berries that are supplied from a producer in clear plastic trays with a snap-on lid.
These safe foods may have been packaged, but they have not been “processed”. They are what they seem to be, and have no “ingredients” label. They may have been washed, and may even have been held in special storage conditions, but there is nothing that has been added to them.
Hamburger is another matter. How do you make hamburger? Obviously, you put meat into a grinder where it is extruded through a plate with holes in it and a rotating knife slices the extruded meat into short pieces. As simple as that? Well, not entirely, since you will see labels on the hamburger packages that tell of fat content, as a percentage of the total, and in some places, there will also be a water percentage. So this tells you that the operator feeds not only meat, but fat into the grinder, and also adds some water. And some hamburger was obviously packaged in a factory, so it was processed there, too. But do they tell you of the other items they process in that factory?
It is best to avoid any factory packaged meats until you have a heart-to-heart discussion with company representatives who are open, honest, knowledgeable, and thorough, and can give you excellent assurances that their product will have no possible chance for cross contamination with gluten.
Some people have suggested that the feeds used for farm-raised fish and shrimp can have enough gluten protein that the fish absorb protein fragments (peptide chains) that remain behind in the fish filets when they are prepared. I have seen no direct evidence that this is a problem, but if you have choices, wild-caught HAS to be safer than farmed.
Once you leave the realm of unprocessed foods you enter into a gray area of processed foods that may or may not contain gluten. Gluten can be included in a processed food by a variety of surprising paths – mostly in ingredients that don’t tell you what they are made from.
One incredible ingredient is called “natural flavor” or “natural flavoring”; this catch-all includes a whole spectrum of food derivatives, such as orange oil or other fruit flavors, but can also include meat-like flavorings. This latter category is the source of a lot of misery.
A very potent meat flavor enhancer is made from “browned protein”. There is a well known chemical reaction that occurs when meat is heated to a temperature that causes it to turn brown – the Maillard Reaction, named after the chemist who figured out what was happening to the proteins. The incredible result is the development of an incredibly pleasing grilled-steak-like flavor, even when the protein is not from a steak.
What some enterprising flavorists discovered was that if you extract the gluten protein from wheat flour, dry it out, grind it up, and cook it to the right temperature, you cause a Maillard Reaction to take place, and suddenly you have a material that you can add in small amounts to otherwise flavorless processed foods, and suddenly have incredibly good tasting stuff. The reaction does NOT change the material from being gluten protein, so it is definitely NOT SAFE to eat foods made with this “natural flavor”. (What could be more natural than something taken out of a plant seed and cooked?)
The most pure substance in the typical home is cane sugar. Surprisingly, it has less non-sugar chemical in it than any other substance used in the home, businesses, and even research chemical laboratories. This is so because of the method used for extraction, concentration, cleaning, purification and packaging of sugar. Basically, a concentrated solution of sugar is further concentrated through evaporation until crystals form. If you do this correctly, the crystals formed are perfect, excluding all other chemicals from the regular packing of the molecules in a regular three-dimensional pattern. When the crystals are big enough, the surrounding liquid, containing all the contaminants, is washed away with clean water. The crystals are then dissolved again, made into a concentrated solution again, and then further concentrated to make more crystals form. Repeat this process several times ,and you can achieve incredible purity.
Most of us have the notion that distilling a liquid makes it totally pure, as well. But this is just not true, since the process actually just concentrates the desired liquid, without eliminating all other substances. The problem stems from the practicalities and physics of distilling stuff. Pure liquids boil at a particular temperature. When they are mixed with other liquids, the boiling temperature of the mixture is somewhere between the boiling temperatures of the original liquids. When you boil a liquid, turning it into a gas, and then condense the vapors on a cold surface, the vapors (gas) turns to liquid again. This should remove other liquids and solids from the resulting liquid (distillate).
The reality is that ALL the liquids in the boiling mix evaporate to some extent, and condense on the cooled surface, turning again into liquid. So the liquid you want to concentrate may be induced to condense more selectively by controlling the condensing surface temperature. But what you cannot control is the boiling of the starting liquid .