First posted Feb 28, 2019
Republished with additional content August 20, 2019
In my previous post, I stressed how the alchemy of food is as much about how we view the ingredients as it is about our technical treatment of them. For instance: the morbid assemblage of bones in my freezer—apparent trash—becomes a bone broth that’s better than anything you can buy. Here, I want to dip a little further into the science of how that sea-change occurs, offering some morsels of history along the way.
Although I slow-cook my leftover bones and vegetable scraps to simply make stock which will then later be used for soups and what have you, the approach of using leftovers to create soups and stews for that day’s meal is a time-honored tradition, probably born out of necessity more than for taste. Throughout much of history, people who had very little in the way of ingredients were able to create a satisfying meal by combining whatever they had in a single pot. For instance, in medieval European cookery, the “perpetual stew” or “hunter’s stew” was one into which just about anything was thrown and cooked, well, almost perpetually, as the pot was rarely emptied all the way and the ingredients and liquid were continually topped off. Day after day, you could just spoon out the lush stock studded with chunks of vegetable and meat, and eat around the bones. Or take for instance potlikker (or “pot liquor”), a dish that remains popular in the south and which had emerged from slaves’ need to turn something into nothing. Chef and author Michael Twitty defines it as the “stock that you get from making greens,” but, he says, “it’s more than that–it’s bones, and skin, and marrow…it is a watery graveyard for flora, and fauna, and mineral, and all of it. It’s stinky. It’s foul. It’s earthy.” And yet it’s delicious, and when it was a major source of sustenance for slaves, it provided much-needed nutrients. Pho, ramen, and other soups from all over the globe emerge from such origins and continue to be well-loved today, even though they are no longer a vital means of survival.
Although in his 1869 Le Grand Dictionnaire de Cuisine famed writer and gourmand Alexandre Dumas claims that the “eternal kettle” “has ceased to function” in modern cookery and “is no more” (66-67), as recently as 2014 Chef Chris Santos instituted the practice of the “perpetual stew” at his West Village restaurant Luoro. The aim was, admirably, to develop amazing flavors out of the ingredients that the kitchen was unable to serve that day. He takes what otherwise would have been trash and transmutes it into a base stock for main-dish menus. In fact, he has even begun to serve the Perpetual Stew “broth” at his bar, so that guests can savor it on its own—because it’s that good.
The concept of the perpetual stew also resonates in modern dishes like Nihari, a stew that’s popular in northern India, Pakistan and Bangladesh; in some restaurants of Old Delhi, a few kilos of the Nihari leftover from the day (called taar) is always added to the next day’s pot. Some restaurants boast having an unbroken line of taar that stretches back for over a century.
Now, I don’t keep a pot simmering on my stove for days on end and the contents definitely aren’t a century old, but I do let my stock cook pretty much all day if I have the leisure to, just adding enough water to barely cover the contents of the pot as needed. And, since we can afford to be more picky in a modern kitchen (and modern economy), I strain the stock to use afresh in other recipes, so my guests need not beware bits of bone in the finished dishes.
Roasting: Our Modern English word “roast” comes out of the Middle English “rosten,” and can be traced at least as far back as from the Middle French “rostir,” meaning to cook on or around an open fire for a prolonged period of time. So, like many of our culinary terms, “roasting” has ties to French food culture. Furthermore, like so many of the French techniques that were recorded in cookery books from the Middle Ages (which were created for and reflective of the household practices of the elite), the technique is associated with prestige. The practice was relevant only in kitchens that could afford the time, attention, and large amounts of fuel necessary to feed the flame and continuously turn the large cuts of meat (already in themselves precious due to their cost). Make no mistake, though—the first humanoid who placed meat on a spit over a fire to cook was also engaging in the practice, and humanity would continue to do so for good reason, developing easier and smarter ways of roasting as technology evolved.
Why do we roast? Simply put, by roasting your meat, your vegetables, or—in the case of this blog post, your bones—you’re unlocking depth and complexity of flavor and aroma. This is due to the fact that the protein in the bones allow for them to undergo the Maillard reaction, which refers to the “many small, simultaneous chemical reactions that occur when proteins and sugars in and on your food are transformed by heat, producing new flavors, aromas, and colors.” Without the roasting step, your stock will fall somewhat flat, leaving you unsatisfied for reasons you can’t quite put your finger on.
Deglazing: Once the materials in the pan have roasted, they go into the stock pot. But what about the caramelized bits left behind, stuck to the bottom of the sheet pan? In French cuisine, these browned bits are called fond , and I like to think it’s because it deserves our fondness—it deserves the effort to extract its flavor. That’s where deglazing comes in. Almost any liquid will do, but I stick with water for a basic broth, but vary it using wine, juice, beer, vinegar—whatever you want!—as the flavor you desire dictates. You just turn the heat on the pan up to high, add the liquid, and gently but constantly scrape at the caramelized bits, until they loosen and become one with the liquid.
Skimming: Many stock recipes you’ll see will tell you to skim the “scum” or “impurities” from the top as the stock comes to a boil. The so-called scum is actually denatured protein, and its only crime is that it’s aesthetically unappealing. I eschew the process of skimming as it first starts to boil, even though that is common practice, because I am generally not concerned with the clearness or color of the bone broth—just the flavor, which I find to be identical with or without skimming. 
Slow-Cooking: Simmering the stock for hours gets every bit of flavor and nutritional benefits out of the bones, leaving you with a super rich, golden stock.
. Eric Schulze, “An Introduction to the Maillard Reaction: The Science of Browning, Aroma, and Flavor,” Serious Eats, 2017.
. To be truly accurate, the browned bits are called sucs in real French cuisine, and the “sauce” created by deglazing it is the fond, which, in spite of my cute mnemonic, actually means “base” or “foundation.” In the United States, however, food culture conflates the two things, and so if you hear an American chef talking about fond, they’re talking about the caramelized stuff at the bottom of a pot or pan. Also, make sure never to confuse fond for burnt; you can deglaze a pan to prevent dried and browned juices from burning and to extra their flavor, but if you deglaze a pan with burnt material stuck at the bottom, you’ll just have a pan full of acrid vileness.
. If you have the desire to commit to skimming, however, see Namiko Chen, “How to Skim off the Scum and Fat from Soups and Stocks,” Just One Cookbook, 2011.
. Similarly, some recipes might call for you to blanch bones in order to remove impurities. I have never found the need to do this, but for another take on it, see Rochelle Bilow’s “Bone Broth: You’ve Been Doing it Wrong (Well, If You Make These Common Mistakes),” Bon Appetit, 2016.