Barley and bulgur are both ancient Mediterranean grains. Bulgur is wheat that has been cracked to cook more quickly, and to achieve a finer texture. Barley is a healthy, nutty, inexpensive grain that isn't used as commonly as wheat, despite its virtues. Substituting barley for bulgur in recipes may change the way a dish is prepared, and will also change its flavor. Despite these changes, barley does work well in many recipes that typically use bulgur, such as tabouli and kibbe.
Differences in Cooking
Barley is prepared by boiling water, adding the grain, lowering the heat, covering the pan and cooking for 20 to 30 minutes, until all the liquid is absorbed. Bulgur is prepared by pouring boiling water over cracked wheat and letting it sit for about 20 minutes. Alternately, you can use cold water and let it sit for a few hours. If you substitute barley for bulgur in a recipe that provides steps for preparing the bulgur, adjust these steps to correspond to the process for cooking barley.
Differences in Flavor
Bulgur and barley have similar flavors but they do not taste quite the same. Despite minor differences in flavor, both grains are used in traditional Mediterranean and Near Eastern recipes, and they are typically used with many of the same ingredients and flavors. Both bulgur and barley go well with olive oil, mint, lemon and garlic. From the perspective of flavor, it makes perfect sense to replace bulgur with barley.
The Gluten Issue
If you want to replace bulgur with barley because you are allergic to wheat, this substitution may not help you if you are looking for a gluten-free alternative: barley, like the wheat that is cracked to make bulgur, contains gluten. If you are allergic to wheat but not necessarily allergic to gluten, barley may be a better grain for you to use.
A 3.5-ounce serving of barley has more than four times as many calories as the same size serving of bulgur, and more than three times as many grams of carbohydrates. However, barley offers other nutritional benefits compared to bulgur: barley has four times as much protein as bulgur, and four times as much dietary fiber. From a nutritional standpoint, deciding whether to replace bulgur with barley should depend on which of these types of nutrients is most important to you.