Whenever I'm writing a recipe, I try to make the ingredient list as flexible as possible. I know that there is nothing more annoying than having to track down an unfamiliar ingredient, paying extra to have it shipped, then having to wait for it to show up before you make the recipe, for which you only need one tablespoon, which leaves the rest of the bottle to languish in the back of the pantry until spring cleaning two years later, when it gets the Marie Kondo treatment, along with all those CDs, mismatched socks, and collections of old National Geographics. It's just the worst.
And while I'll usually list lots of possible substitutions, there are a few ingredients that just can't be replaced. That's why I've dedicated this whole post to sumac—I really believe it's worth it to have a jar in your pantry, especially if you want to regularly cook Middle Eastern food.
Sumac (also spelled sumaq or sumach) is made from the ground-up pods of the sumac shrub. It adds a wonderfully tangy, subtly bitter flavor to whatever it's dusted over. It tastes acidic, but without tasting like citrus or vinegar. An added bonus is the dramatic color, which ranges from tawny red to burgundy, and adds a pop of color to a humble plate of hummus or labneh. It's a staple of Middle Eastern cuisine (as well as many other cuisines around the world) and can be used wherever a little extra tartness is called for. I use it in the following recipes, so feel free to visit these pages if you're looking for a way to use up a stockpile of sumac:
But all of this is not to say that sumac is never replaceable. In certain recipes, lemon will add the necessary tartness, and the sumac won't entirely be missed. But sumac adds a distinctive flavor that just isn't exactly the same as lemon. Some dishes, where sumac is the star, simply can't be made without it. Take fattoush/fattoushie. If you don't have sumac, you might as well choose another salad (although you shouldn't worry, because there are plenty of Middle Eastern salads that don't require sumac).
But the good news is that sumac is relatively inexpensive and easy to find online, and once you buy it, you will start putting it on everything (popcorn, garden salads, grilled veggies, grilled meats, burgers, fish, cheese sandwiches, lentil soup...). When I want to treat myself, I like to shop at the Spice House (my top recommendation), which sells phenomenally high quality goods at a very reasonable price. If you can find it in a Middle Eastern grocery store, it will be even more affordable. The market near me sells sumac for a couple dollars for a decent-sized bag.