In theory and practice

If it wasn’t for the tomatoes, the BLT sandwich could be a four-season delight. But the tomatoes that it contains must be fresh, which limits when the bacon, lettuce and tomato sandwich is available.

The BLT doesn’t just depend on the tomato. It serves as a stage to display it, a vehicle to enjoy one of the best parts of summer.

The ideal tomato is one that necessitates a bib when you’re eating the sandwich that delivers it. 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, there is bread and mayo. I believe onions fall into this category as well. But nobody wants to say BLOMBT.

It wouldn’t be hyperbole to say that the many parts of the BLT add up to something even greater then their sum. It might even be an understatement to call it a freak of nature. I’ve seen a BLT break two laws of the universe simultaneously, as it is powerful enough to entice my wife to eat both mayo and bacon, two foods from which she would otherwise flee.

Somewhere, I suspect, there is a gluten-intolerant vegan who has made an exception for a BLT. At the very least, surely many have fantasized about it, especially in summertime when the tomatoes are ripe.

According to current theory on taste, the human body is wired to detect at least five basic tastes: salty, sweet, sour, umami and bitter. Impressively, a BLT contains all.

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 higher in a ripe tomato than in many shellfish, including scallops, mussels and oysters.

Tomatoes also interact spectacularly with the BLT’s other ingredients, including salt and fat. Fat, while not officially recognized as a basic taste, might be on the verge of becoming one. A case for fat as taste, long simmering, was recently strengthened by research that found people can smell pure fat. Whether or not it’s an official taste, there’s no question 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) and 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 as well.

Bread is the only element of the BLT with which the tomato clashes. It contributes sweet, salt and umami, 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 mayo, undermine the bread’s job by soaking through it and destroying its structural integrity. This is why the bread is usually toasted.

But toasting can create problems too. It can scratch the roof of your mouth, especially if you’re eating with the abandon of a shark at a feeding frenzy

BLT lovers, and lovers of all sandwiches, really, would benefit from an elegant trick that I learned from a farmer friend who purports to be an expert on BLTs. At the very least he cites them as an excuse when I give him a hard time about how much iceberg lettuce he grows.

I call him El Jefe. His wife calls him El Hefty. His trick is to toast one side of each slice of bread, and position those two sides facing inward, where they can withstand the gooey onslaught of the 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.

Part of the power of the BLT resides in the redundancy of its many flavor components. With umami coming from bacon, tomato, mayo and bread, for example, multiple layers of umami blend together, creating an umami continuum. Acid, likewise, comes from both tomatoes and mayo, while sweetness comes from tomato, mayo and bread.

You can further the layering of similar flavors by using slices from multiple varieties of tomatoes, if you’ve got them. Avoid low-acid tomatoes like Brandywines, in favor of high-acid varieties, like beefsteak.

While the redundant complexity of the flavors in a BLT makes for both contrast and harmony, the various textures involved offer nothing but contrast. In terms of texture, each component contributes something completely different and unique that isn’t analogous to anything else. The crisp of lettuce, the supple crunch of the bread, the slimy lubrication of the mayo, the greasy chewiness of the bacon, and the exploding juice of the tomato are all going in different directions at once, perfectly.

It’s hard to mess up a BLT. Just don’t burn the bacon or toast. Do not use Miracle Whip. Add avocado if you wish. And be very picky about the tomatoes.