At its most basic definition gluten is a protein that consists of a combination of two component proteins, gliadin and glutenin. Gluten occurs naturally in the grains wheat, barley, and rye.
Foods made with wheat, barley, and rye will contain gluten. This includes most pasta, breads, cakes, and many desserts.
Processed foods that are made using the ground flours of wheat, barley, and rye will also contain gluten. Some alcoholic beverages such as beer that is made from barley and whiskey that is made from rye will contain small amounts of gluten.
Gluten is easily identified as the sticky substance in unbaked bread and pizza dough that gives the dough its elasticity and ability to stretch when you knead it. It is also the substance that gives baked bread its spongy ‘spring’. This springy structure can be approximated in gluten-free products by using an additive called xanthan gum.
Those who are gluten intolerant need to remove gluten from their diet or they will risk intestinal damage. Nearly all foods that normally contain gluten - including pasta - can be made without gluten-containing ingredients. There are gluten-free grains that can be substituted for wheat, barley, and rye so you will still be able to enjoy pasta, breads, cakes, desserts, and even a (gluten-free) beer.