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The Food Lab: Vegetables, Salt, and the Science of Perfect Gazpacho
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As anybody who's seen the best episode of The Simpson's ever knows, gazpacho is tomato soup, served ice cold,* right? Well, sort of. True, these days pretty much every gazpacho you find in restaurants stateside is made by pureeing tomatoes, cucumbers, peppers, onions, and garlic into a soup ranging from smooth to chunky, but that's not really what gazpacho is all about.
*I know, I know... Go back to Russia.
Here's what most people think when they hear the word:
But here is where gazpacho started:
That's right. Stale bread and olive oil. It's not quite clear exactly where the origins of gazpacho lie—some folks say it's the Moors, others the Romans—but one thing is certainly true: people had been eating versions of bread and olive oil soup in the Spanish region for centuries before the tomato even existed in Spain. These days, you'll find gazpacho of all flavors and makes, ranging from white gazpachos made of almonds and grapes, to the Andalusian classic made with tomatoes.
What's the point? you may ask. Who cares if the soup started as bread and olive oil base that then eventually got vegetables added to it? And I'm with you—as long as it's delicious, who really cares where it came from.
Well, the reason I care is that all too often recipes for so-called "gazpachos," or those served in restaurants contain no bread or olive oil at all, turning them into nothing more than watered down salsas. And sure, sometimes this can be tasty but I've never had a watered-down-salsa-gazpacho that can hold a candle to the creamy, smooth, intensely olive-oil flavored, rich-yet-refreshing Andalusian version.
Now, you may think making great gazpacho is as simple as throwing a bunch of vegetables, bread, and olive oil into the blender. And given that you have awesome vegetables (and now is the perfect time to get awesome vegetables), that's pretty much true. But there's a difference between great gazpacho and perfect gazpacho. It's the latter we're after.
Good Tomato, Bad Tomato
First things first: vegetables. Andalusian gazpacho is typically made with a combination of tomatoes, peppers (I like green, you can use whatever color you'd like), onions (red onions offer the best balance of sweetness and flavor), garlic, and cucumber. Most of these are simple. It's the tomatoes that can prove a bit of a problem.
See, the thing is, a few decades ago, tomato farmers realized that more than anything else, the two things that compel a consumer to buy one tomato over another is ruby red color and perfectly spherical shape. Thus they've been hard at work getting tomatoes to look red and be round, completely ignoring something else in the breeding process, namely flavor.
Couple this with the fact that a perfectly ripe tomato is nearly impossible to ship because of its delicate flesh and skin, and you're in trouble. What we've got is a country full of relatively bland tomatoes that are picked while still completely green and hard, brought to market, then artificially ripened by being gassed with ethylene (that's a gas produced naturally by ripening fruits). It's no wonder supermarket tomatoes taste the way they do.
Your best bet for finding quality tomatoes is a) to grow them yourself (surprisingly easy, given enough sunlight), or b) check out your local farmers' market. I don't buy too far into the whole local/seasonal thing most of the time (cucumbers, for example, taste just about the same to me year round, or even when they're just out of my own garden), but tomatoes are one vegetable that are simply not worth eating most of the year.
Don't bother making gazpacho in the winter or spring.
With a Pinch of Salt
As an uncooked soup, once you've got the vegetables back in your kitchen, your goal is to extract as much flavor from them as possible. In order to do this, let's take a little closer look inside them, shall we?
Now, anyone who's taken third grade science and looked through a microscope knows that vegetables are composed of cells. These cells have thick, pectin-strengthened walls and are filled mostly with water, along with pigments and flavorful compounds. While trapped inside the cell walls, we can't really smell or taste these compounds. Unfortunately, cells are tough characters, and the flavorful compounds are stuck tightly inside them.
Our goal: to orchestrate a jail break and make sure that all that flavor comes out of the cells and into our noses and mouths where they belong.
Simple mechanical action (I.E. tossing everything into a blender) works pretty well. Many of the cells are ruptured, spilling out their contents, but not all of them. We can do better. Rather than simply trying to smash the cells apart to release their water (and thus their water-soluble flavor compounds), why don't we find a way to bring the water out to us? Salt is the key.
I chopped up identical batches of vegetables and placed them in bowls. One of them was left plain, while the other was tossed with a bit of kosher salt. Half an hour later, the picture above is what I saw. It's one of the most effective uses of salt, and it all has to do with a thing called osmosis.
Water is a fickle lover. Given the opportunity, it likes to spread itself around evenly. Normally, it sits around safely inside the vegetables' cells, keeping all those flavor compounds company. With no competition from the outside, it's content. But once we add a few salt molecules to the outside of the cell membrane, the water feels compelled to share itself with the salt as well. Water migrates out from inside the cell walls, bringing along some of those flavorful compounds for a salt-water-flavor threesome.
It's a pretty significant amount of liquid that comes out, all of it tasty. Indeed, in a blind side-by-side taste test between vegetables that had been salted for a half hour then blended with bread and olive oil vs. vegetables that were blended then salted afterward (I used the same amount of vegetables and salt in both), the salted-and-rested-then-blended vegetables were picked unanimously over the blended-then-salted version.
Better, but could we take this even further?
Breaking The Ice
One sure way to extract as much flavor as possible from a vegetable is to cook it. The process breaks down cell structure and releases most of the cells' contents. Unfortunately, cooking also triggers chemical reactions that drastically alter the flavor of vegetables. No matter what Lisa says, gazpacho is not simply tomato sou served cold—it's a raw tomato soup served cold.
But what if there were another way to rupture cells? The next thought that struck me came from my friend Aki and Alex over on the awesome blog Ideas In Food: Cryo-blanching, essentially a fancy-sounding word for freezing.
When they perform cryo-blanching, they vacuum seal vegetables in airtight bags before placing them in the freezer. The idea is that as ice forms inside the vegetables' cells, the sharp, jagged crystals end up rupturing and weakening the walls of the cells. What you end up with is a vegetable that's soft as if it's been cooked, but still retains its fresh, raw flavor. Why not use the same method to disrupt the cell structure of the vegetables for my gazpacho?
I gave it a shot. First, I salted my vegetables as usual, allowing liquid to be extracted. After, I placed the vegetables on a sheet tray and stuck them in the freezer until they were frozen. After thawing, sure enough, even more liquid came out of them; I ended up with nearly twice as much as the plain salted vegetables.
Now I know that you must have heard hundreds of times that you should never put a tomato in the refrigerator, much less the freezer, and that's usually true. Tomatoes have some pretty soft-skinned enzymes that can be destroyed at low temperatures. These enzymes are responsible for catalyzing some of the ripening reactions that help the tomato develop its characteristic flavor. Additionally, chilling tomatoes can cause some of their cell walls to weaken, making them grainy or mushy instead of fleshy and smooth.
But for gazpacho, neither of these effects matters much. First off, we're starting with already-ripe tomatoes, so their flavor should already be fully developed. Subsequent freezing won't harm this. Secondly, we're pureeing them until completely blended anyway. We want their cells to weaken!
Blending the cryo-blanched vegetables up along with their extracted juice proved to be the most flavorful batch of gazpacho yet.
As far as flavoring goes, you can feel free to add whatever you'd like. I like to keep mine simple, using a significant amount of olive oil (drizzling it in slowly while the soup spins in the blender helps keep it smooth and emulsified), a splash of sherry vinegar, and a sprinkling of black pepper and chives on the finished soup.
If you're into chunky versions, get some extra vegetables and cut them into a fine dice then add them back to the finished soup. You'll get a much better texture than the standard blend-until-still-half-chunky method. The soup that results from that method always reminds me of a tomato Slurpee. Not too appetizing.
So is this soup going to be able to replace the slow roasted suckling pig at your next BBBQ*? Certainly not. But with vegan month coming up soon (yeah, I'm gonna go there), I'll be glad to have this one under my belt.
*The extra B is for BYOBB.