SALTY, SWEET, SOUR, BITTER AND DELICIOUS The BLT succeeds because of its harmonious combination of flavors and textures. But that's a lot of mayo on this one.
If it wasn't for the tomato, the BLT sandwich would be a four-season delight. But the tomatoes must be fresh, which limits when the sandwich is available.
The BLT doesn't just depend on the tomato. It serves as a stage on which to display it and as a way to enjoy one of the best parts of summer.
The ideal tomato is one that requires you to wear a bib when you eat the sandwich. But in addition to its refreshing juices, the tomato brings a cocktail of flavors that interact with the BLT's other ingredients, including the mayo and bread, which are so essential that they can go without mention in the sandwich's name. After all, if it is a sandwich, then there is bread and there is mayo. I believe onions fall into this category as well. But nobody wants to say BLOMBT.
According to current theory on taste perception, the human body is wired to detect at least five basic tastes: salty, sweet, sour, umami and bitter. Impressively, a BLT contains all of these.
Most of these tastes are easy to detect, but the amount of bitter, which happens to be the only basic taste to which people often object, is low. Slight bitter notes come from the lettuce, onion and the mustard powder that's in most mayo formulations, and at these low levels they add an earthy base to the BLT without making the sandwich itself taste bitter.
Tomatoes contribute sweet and sour, as well as a surprising amount of umami, to the equation. Umami is measured by the amount of free glutamate, the levels of which are high in a ripe tomato.
Tomatoes also interact spectacularly with the BLT's other ingredients, including salt and fat, which bacon contributes. Fat, while not officially recognized as a basic taste, might be on the verge of becoming one. Whether or not it's an official basic taste, there's no question that fat makes things taste better.
Mayonnaise is mostly fat, but like the BLT, it contains every basic taste: sweet (most recipes have some added sweetener), sour (from the lemon or vinegar), bitter (from the mustard powder) umami (from egg yolk) and salt. Mayo also provides an important layer of lubricant that helps all of these layers merge together in your mouth. And like the bacon, onion and lettuce, mayonnaise mixes harmoniously with the tomato.
Bread contributes sweet, salt and umami tastes to the overall flavor of the sandwich, but its most important attribute is to function as a skin that holds the other ingredients together long enough for you to eat them. Tomatoes, along with the mayo, undermine the bread's job by soaking through the bread and destroying its structural integrity. This is why the bread is usually toasted.
BLT lovers—and lovers of all sandwiches, really—would benefit from an elegant trick that I learned from a farmer friend. Toast one side of each slice of bread and position the two sides facing inward, where they can withstand the onslaught of tomato and mayo. The untoasted sides face the outside, where they're soft as white gloves on the inside of your mouth.
To toast just one side of each slice, you can either squeeze two slices into the same toaster slot, or arrange them side-by-side under the broiler.
It's hard to mess up a BLT. Just don't burn the bacon or toast.
Add avocado if you wish. Use whatever bread you want, and be very picky about the tomatoes. And most important, don't use Miracle Whip.