The Food Lab: A Better Way to Caramelize Onions (Plus, French Onion Dip!)
Disclaimer: Although we do talk about French onion dip here, this article is really more about the general application of caramelizing onions.
Like the He-Man Christmas Special, French onion dip is one of those things that's difficult to admit that you secretly really love. I mean, it's essentially mayonnaise that's designed specifically to make your breath smell really bad. On top of that, most commercial versions have a goopy texture and underlying backbone of dehydrated onion flavor that makes them quite hard to take seriously. Then again, who amongst you hasn't dipped your way through a jar of it while watching reruns of Mr. Wizard's World by yourself because your wife a) won't watch them with you and b) has moderately sensitive olfactory sensory apparatus* that oddly prefers fresh air to onion breath? Who, I ask?
Wouldn't it be great if there were a French onion dip that we didn't have to be mildly ashamed to consume in public? Preferably one made with real onions?
There are certainly no shortage of recipes out there, and the general method, unsurprisingly, begins with the same basic technique: cook down finely chopped onions over low, low heat to get their natural sugars to slowly and evenly caramelize. Once the onions are completely broken down to a deep brown, jam-like consistency, they're blended together with mayonnaise and sour cream, seasoned with a bit of salt and pepper, and you're done.
It's a simple process, and the results are infinitely better than any jarred versions, but my quibble with it is the same one that I have with French onion soup: it's a major pain in the cul. All that slow caramelizing takes a good 30 to 45 minutes of constant pot babysitting. Let it go just a bit too long or step away for five minutes, and you've burnt your onions, making the final product too bitter to use.
As with exercise and marriage I often think about how great it'd be if there were a method that could deliver the exact same (or better!) results without the massive time commitment.
It took me a week of cooking and over 20 pounds of onions to figure it out how.
First things first: What type of onion works best?
There are five basic onion varieties available in my local supermarkets: red, yellow, white, and sweet (either Vidalia or Walla Walla). You'd think that sweet onions are the way to go, offering you more sugars to caramelize, but upon cooking all four onion varieties side by side, the differences were less pronounced than I expected. All of them developed rich, caramelized flavor in about the same amount of time, but the red turned an off-putting muddy greenish-brown color. Ick. The sweet ones were marginally sweeter, but not enough that they were worth the premium price. They also lacked complexity. Of all of them, the yellow boasted the most flavor.
Turns out that although sweet onions have about 25% more sugar in them, their flavor difference when raw has more to do with the amount of tear-inducing lachrymators they contain. Yellow onions have more pungent irritants than sweet, giving sweet onions the impression of actually being even sweeter than they really are. When you cook the onions down, these pungent compounds mellow out into more complex flavors, giving yellow onions a distinct edge over the sweet.
Before we can figure out how to improve our end results, it's important to understand exactly what's going on when an onion browns.
- First, the onions begin by sweating. As they slowly heat up, moisture from their interior (they are roughly 75% water by weight) begins to evaporate, forcing its way out of the onion's cells, and causing them to rupture in the process. This breakdown of the cells is what causes onions to soften during the initial stages of cooking.
- As onion cells continue to break down, they release their contents, a complex mix of sugars, proteins, and aromatic compounds ( mercaptans, disulfides, trisulfides, thiopenes, and other such long, no-reason-to-memorize chemicals). This is when things start to smell really good, and incidentally, when you should get the dog to leave the room, unless you enjoy a permanent onion aroma on your pet's fur.
- Once most of the liquid has evaporated and the temperature of the onion starts creeping up into the 230°F-and-above zone, caramelization begins to take place. This reaction involves the oxidation of sugar, which breaks down and forms dozens of new compounds, adding depth of flavor to your onions. Large sugar molecules like sucrose break down into small monosaccharides like glucose and fructose. Glucose and fructose separately are sweeter than a single sucrose molecule, making the overall flavor of caramelized sugars sweeter than the starting sugar.
- At the same time, the Maillard reaction takes place. Similarly to caramelization, the Maillard reaction will cause browning. However, the Maillard reaction is far more complex, involving the interaction of sugars, proteins, and enzymes. The products of the Maillard reaction number in the hundreds, and are still not fully identified. This is the reaction that causes browning on your toast or your steak when you cook it.
- Ideally, as the onion continues to cook, three things will complete themselves at the same time: 1: the complete softening of the onion's cell structure, 2: maximum caramelization (I.E. as brown as you can get before bitter products begin to develop), and 3: maximum Maillard browning (with the same caveat)
By enhancing and speeding up each of these stages, I should be able to improve my overall process.
Mission 1: Increase the Effects of Caramelization
The most obvious way to do this is to increase the amount of sugar we start with. The sugars in onions are glucose, fructose, and sucrose (a combination of one glucose and one fructose molecule)— exactly the same as the caramelization products of table sugar. Indeed, I found that adding just a touch of table sugar to the onions increased sweetness without affecting the overall flavor profile of the finished product.
On the other hand, it didn't speed things up at all the way I wanted it to. But what if I gave the caramelization a kick-start by cooking the sugar on its own before adding the onions?
I tried it, cooking the sugar down in a dry skillet until it reached a deep golden brown before adding the onions and tossing them to coat them in the hot caramel. It worked like a charm, shaving a good 4 to 5 minutes off of my total cooking time, and giving me sweeter, more deeply caramelized end results.
Mission 2: Increase the Maillard Reaction
There are a number of things that affect the maillard reaction, but the overriding factors are temperature and pH. For now, I had no safe way to increase the temperature—cook the onions too hot, and the small pieces burn on their exterior before the interiors have a chance to release their chemicals. Low and slow is the only way to go.
pH, on the other hand, I've got a bit of control over. In general, the higher the pH (I.E. the more basic or alkaline), the faster the reaction takes place. I remember reading a story a couple years ago on Khymos.org in which the author managed to speed up the cooking time of onions by adding a pinch of baking soda, a powdered base.
Indeed, in my testing on chicken wings, I found that adding baking soda to the skin can greatly increase browning. It also gave me chicken wings an odd chemical aftertaste. Would it work better with the onions?
The key is moderation. While large amounts of baking soda dramatically increased the browning rate (by over 50%!), any more than a 1/4 teaspoon per pound of chopped onions proved to be too much.
You may also notice that the baking-powdered onions are much softer. This is because pectin, the chemical glue that holds vegetable cells together weakens in higher pHs. That's why many British recipes for mushy peas calls for a soak in water dosed with baking powder (for similar reasons, you can par-boil potatoes in vinegar-spiked water to tenderize them without letting them break down).
Faster breakdown means faster release of chemicals, which means faster overall cooking.
Mission 2: Accomplished. We're almost there!
Playing With Fire
Mission 3: Increase the Heat
Back to heat. As I mentioned, the problem with increasing the heat to much higher than medium-low is that the onions begin to cook unevenly. Some bits and edges will start to blacken long before other bits even reach the golden brown stage. Additionally, the sticky sugars and proteins that get stuck to the bottom of the pan as the onions cook rapidly turn dark brown due to their direct contact.
So the question is: if you're cooking with high heat, what can you do to simultaneously even out the cooking across all the onions, to remove the sticky browned gunk from the bottom of the pan, and to regulate the overall temperature so that nothing burns?
If you've ever made a pan sauce, the answer is so blindingly simple that I'm surprised it's not completely common practice: just add water.
At first, adding water may seem counterproductive: it cools down the onions and the pan, forcing you to expend valuable energy heating it up and evaporating it.
But here's the deal. Both the browned patina on the bottom of the pan and the browned bits on the edges of the onions are made of water-soluble sugar-based compounds that happen to be concentrated in a single area. By adding just a small amount of liquid to the pan at regular intervals, these compounds get dissolved and redistributed evenly throughout the onions and pan. Even distribution leads to even cooking, which leads to no single part burning before the rest is cooked.
So what does this all mean for your onions? It means that you can cook them over a much higher flame (medium high works well—even maximum flame is feasible, though it requires a little attention) and every time they threaten to start burning, just add a couple tablespoons of water to even out the cooking, and you're smooth-sailing once again.
Mission 4: Accomplished
Building the Dip
So with a couple of little tweaks, I'd managed to whittle down a 45-minute long procedure to not much more than 15 or 20 minutes, and to be honest, the flavor developed in that short amount of time is actually deeper and more complex than the standard, slow-cooked French onion soup method (incidentally, this process is perfectly adaptable to onion soup—just add a splash of sherry and some good chicken or beef stock to the onion base and simmer it down for a few minutes. Delicious!)
All that remained was to create a creamy dip for the intensely onion-y flavor base.
I messed around a bit with softening cream cheese, strained yogurt, and crème fraîche, but in the end, none of them were better than the traditional blend of sour cream and mayonnaise. A splash of lemon juice added some brightness while a bit of Worcestershire sauce gave it a meaty, umami-ful backbone. Looking to up the umami factor even more, I decided to also add a touch of grated Parmesan cheese.
The good thing about going through 20 pounds of onions in a week is that now the walls, carpet and dog permanently smell like caramelized onions, my lovely wife no longer notices my breath.
*A.K.A. her nose.