Chemistry in Your Kitchen

Matthew Hartings

• Publisher: Royal Society of Chemistry
• Year: 2020
• ISBN:
  9781839162930
• Edition: 1
• Topic: Naturwissenschaften
• Subtopic: Chemie

Whether you know it or not, you become a chemist any time you step into a kitchen. As you cook, you oversee intricate chemical transformations that would test even the most hardened of professional chemists. Focussing on how and why we cook different dishes the way we do, this book introduces basic chemistry through everyday foods and meal preparations. Through its unique meal-by-meal organisation, the book playfully explores the chemistry that turns our food into meals. Topics covered range from roasting coffee beans to scrambling eggs and gluten development in breads. The book features many experiments that you can try in your own kitchen, such as exploring the melting properties of cheese, retaining flavour when cooking and pairing wines with foods. Through molecular chemistry, biology, neuroscience, physics and agriculture, the author discusses various aspects of cooking and food preparation. This is a fascinating read for anyone interested in the science behind cooking.

Breakfast

CHAPTER 1

Coffee

We start with a humble cup of coffee.

A simple act that is repeated around the world over 2 billion times a day,¹ brewing and drinking a cup of coffee can seem to many as reflexive as blinking, yawning, or taking a look at their phones in the middle of a meeting.

And yet, to get from the farm to your face, a coffee bean must become a player in a well-conducted symphony of chemistry.

This description does not aim to highlight the single-sourced, fair trade, small-batch roasted, hand ground, 30 g of beans, and 300 mL of 88 °C water Pour-Over coffee produced by the barista who knows more about coffee than any human really should. No, every little bit of coffee – from the most lackluster, office break-room swill to that over-crafted Pour-Over – is chemistry in a cup.

As a chemist, I am continuously amazed and inspired by the intricate chemical processes that are required to complete even the most unpretentious recipe. I am in awe of every cook who, when in the kitchen, masters an interconnected network of competing chemical reactions. These same reactions, when written and diagramed, would send even the most grizzled laboratory veteran running for the hills.

Because of this, I see cooking as a vehicle for having a conversation about chemistry with people who would normally rather not think about it. The sheer number of people who are willing to seek out that singular barista or who meticulously experiment with their own recipes are testament to this. In fact, of all of the things I have written, the piece that has received the most attention is a blog post I wrote on the science of gin and tonic.² I think that it struck such a nerve because there are a lot of people out there who are passionate about gin, tonic, and gin and tonic. And, because of this passion, I was able to pose a really intriguing question: Why do gins and tonics taste so different on their own, but are inherently ‘gin and tonic-y’ when mixed together in a drink? What is the chemistry that controls this experience? I’m not entirely sure that I adequately answered that question in my blog post, (you can be sure that I will revisit gin and tonic later in this book); but, using a simple cocktail, I was able to discuss van der Waals interactions, protein-ligand binding thermodynamics, and neurochemistry with people who would normally be completely turned off by such topics. As the Pulitzer Prize-winning journalist, Deborah Blum, noted in a previous interview with me, “[Chemistry is not just] the story of some weird experiment done in a distant lab. It’s the story of dinner, or something equally ordinary and therefore important.”³ I must admit that I agree with her sentiments. I find that there is an incredible amount of beauty and elegance in the chemistry of the common.

Another reason why food science topics resonate is the common ground between chemists and non-chemists. Specifically, no one really has a full understanding of what is going on. We (scientists) may have a pretty good clue about things. But, often, there are aspects of cooking chemistry, and cooking science, that elude us. Contrary to what some may believe, the absence of knowledge is very exciting to a scientist. And, as far as kitchen chemistry goes, in the absence of knowledge, science must turn to the people who practice and observe this type of chemistry on a daily basis: professional and home cooks.

In these situations, that elude scientific understanding, the practitioners (roasters, bakers, chefs, mixologists, brewers, and home cooks) are the experts. Scientists do well by listening to them, as I have hopefully done in this book. These people (consciously or not) know the important variables in their recipes. They understand that a specific change in color or texture or aroma can often mean that a recipe is ready to progress to its next step. Their observations are attuned to the food that they are cooking. In this respect, everyone is a chemist when they step into a kitchen. Everyone does chemistry when they cook. And, anyone is capable of making novel discoveries or observations when they are standing in front of an oven. I, for one, have learned a great deal about chemistry by talking with students, friends, relatives, and professional chefs alike. As Chef Gusteau says in Ratatouille, “Anyone can cook.”⁴ The same is true of chemistry. Anyone can be a chemist in the kitchen. For professional food scientists and professional chemists listening to these practitioners can be a very valuable experience.

From another point of view, I believe that cooking can be a great inspiration to chemists. Research chemistry is constantly moving from clean experiments to systems that are convoluted and complex and messier than their predecessors. Cooking is complex chemistry. Cooking can help to illuminate problems that I am having in my own lab. I see food as a lens through which I can learn how to be more creative in research. The cooking that humans have been doing for millennia can give clues towards the advancement of chemical science. While it is true that science and cooking have always been connected (the bain-marie, or double boiler, is thought to have been developed by an alchemist named Mary the Jewess⁵), I believe that kitchen chemistry can be a strong inspiration for modern day research.

This book is an exploration of these topics: discussing and sharing the really interesting chemistry that happens in our food because it’s fun and so that we can be better cooks, looking for explanations of what goes on when we cook our food, and exploring the ways that food can teach us about chemical research.

And that brings us back to our cup of coffee. It turns out that this unassuming drink can tell us a lot about the most important processes in making food, it can illustrate how chemistry works, and by understanding these things, it can also show us how we can be better cooks and chemists.

If there were any food in this world where humans might expect to produce consistent “perfection”, coffee might be it. The 2 billion cups that we consume every day is no joke. The practice and repetition that go into all of those vats of java is an undertaking of epic proportion. And yet, it is still exceedingly common to find coffee that doesn’t match up with even our most mediocre expectations.

The quest for perfection also often falls short in coffee shops that are dedicated to finding, and serving, excellence. In Nathan Myhrvold’s tome, Modernist Cuisine, he and his co-authors describe the elusive “god shot” of espresso.⁶ This espresso is produced with exquisitely roasted beans, in a room at the ideal humidity, with the water at a perfect temperature and pressure and containing the right concentration of magnesium and calcium and carbonate ions,⁷ in the second phase of the moon, while standing on one foot, with your eyes crossed. In the book, Myhrvold laments the infrequency of pulling off the perfect pull. (“Pull” is a term for making espresso that originates from a time when espresso machines required a lever to generate the pressure needed to force water through the coffee grounds.) There are some baristas and coffee pros who refute the notion of a “god shot.”⁸ They claim that most espressos are made well when the baristas are paying a little bit of attention. These professionals think that a “god shot” is more a reflection of the drinker’s mood than anything else. There may be something to this claim, as we will discuss later in this book. But the fact remains that most coffee producers still strive for consistent perfection.

In truth, coffee (the best and the worst) is the result of both chance and controlled chemistry. And, while perfection is at the whim of personal preference, good and really good can be made by paying attention to flavor creation, flavor extraction, and presentation. Put another way: How do coffee berries turn into coffee beans? How do we get the flavor out of the beans and into water? And, how are we most happy when drinking coffee? The first two questions are inherently chemical and, by exploring them in the context of coffee, we can understand the basis for the chemistry of a lot of other food preparation. The final question involves more cultural and neurochemical cues than anything else. However, if we understand what we like (our personal preferences) from the outset, we will better be able to produce that during any type of food preparation.

FLAVOR CREATION

Compass Coffee is a relatively new shop in one DC neighborhood that is being gentrified. The storefront is sitting right on the edge of what is new, and what has suffered years of public neglect. All social commentary aside, Compass is not (yet) in a spot that is ideal for their business. When I went to Compass to talk about roasting coffee beans, it was 10 am on a workday. The line for ordering coffee extended out of the door. As I was early for our meeting, I got in line like everyone else. I struck up a conversation with a gentleman in front of me who was wearing cycling gear. He said that he had never ridden through this neighborhood before and had never heard of this coffee shop. But, when he saw the line, he couldn’t not go in. It’s pretty obvious that the owners were doing something that has struck a nerve.

It was no mistake that I went to Compass for this conversation about coffee and science. Michael Haft and Harrison Suarez, Compass’s owners, had been profiled by the Washington Post and other news outlets for their use of research based methods and analytical data keeping for optimizing their product.⁹ I had also previously interviewed them for Chemical and Engineering News with my journalist friend, Jessica Morrison, for a story on nitrogen infused cold brew.¹⁰ So, I knew that they were up to date on all of their science homework.

Suarez and Haft met in the Marines where they started to share their love of coffee. Neither of them had a strong background of science training. But both of them wanted to do “right” by their coffee. So, they started reading and playing around and learning and experimenting, and learning more. They tell me that, while they may be more analytically minded than some other roasters, that doesn’t mean their process lacks art or any room for taste or personal preference. Michael told me that many see roasting as some mystical process. But science, as they see it, just shows how you can best find your way into these predilections.

When they opened their shop and started putting their team together, they hired Brandon Warner as their head roaster. Suarez said of Warner, “With coffee roasting being as much an art as it is a science, we wanted someone on our team who would come to the process with an open mind. They had to be willing to experiment and to follow what their results showed them.”

And, from what I know about Warner, that describes him pretty well. Warner was an undergraduate psychology major who came to DC to work as a writer. He keeps a trimmed auburn beard and his accent immediately gives him away as a Midwesterner, much like me. Warner said that he had originally gotten into both home beer brewing and home coffee roasting. His small apartment pretty much prevented him from being able to do anything interesting with respect to beer making, and he was shoehorned into roasting coffee, which he did with a cast iron pan. As he played around and got a little better, his techniques and equipment got a little more sophisticated. And now, as head roaster at Compass, he roasts 30 kg of beans at a time.

As we started chatting, I quickly professed an interest in the green coffee beans that they use. Warner hauled over a tub of beans from Guatemala. The tub is about the shape of a trash can, only about half the height – think of a fat R2-D2. Warner pulled the lid off and told me to stick my head in and take a whiff. The smell reminds me, overwhelmingly, of hay, and I immediately think of the freshly cut hay that I would use as a child to feed cows on my family’s small farm This is a very stark childhood memory for me. And, I can’t quite tell if there are any other strong aromas, or if my subconscious is preventing me from smelling anything else. But, honestly, this is kind of what I expected the beans to smell like. I don’t know why. Perhaps it is because of their grassy color and that they look like overgrown hayseeds Next, he pulled out a tub of beans from Ethiopia. I lean over expecting something similar but am completely floored by the difference in smell. These beans have a funkier aroma. They may be funky because I don’t recognize the smell right away. But they smell fruitier and sweeter than the Guatemalan beans. Brandon says that this difference is fairly generalizable between Central and South American beans as compared to beans from Africa.

Coffee is prepared from the fruit of the Coffea plant, which naturally grew in some parts of Africa and southern Asia. It seems as though the caffeine, and our addiction to it, are written into the DNA of Coffea.^11,12 Caffeine is an alkaloid molecule and can be toxic at high enough concentrations. Through natural selection, Coffea plants produce high amounts of caffeine in their leaves. At these increased levels, caffeine will discourage insects from eating coffee leaves. Furthermore, when the leaves fall to the ground and eventually become part of the soil, the high caffeine content in the dirt can prevent other plants from growing near the Coffea tree. And it turns out that Coffea evolution is even sneakier than just making sure that its trees aren’t killed off. Caffeine gets used to ensure successful reproduction as well. Trees that produced caffeine in their flowers and, subsequently, their berries, were more likely to be pollinated. Bees and other pollinators like the hit of caffeine just as much as we do.

For all animals, from insects to mammals, alkaloids are poisonous at high doses. We recognize these molecules as a bitter taste in our mouths. However, at lower doses, alkaloids stimulate positive responses from animals and become addictive. Caffeine is only one example of this. Nicotine, morphine, and cocaine also fall into this class of chemicals. Through evolutionary trial and error, coffee trees found a way to dose their flowers with caffeine so that the pollinating insects that visited these trees would get a little hit of caffeine with their nectar and would want to come back for more. It seems as though our addiction to caffeine is inextricably linked to Coffea killing off its plant competition and warding off harmful insects.

While caffeine may be the reason we continue to go back to coffee (and tea, for that matter), there are other chemistries inherent to the plant and its harvest that are tied to its initial pull on us: the aroma. It’s true that the aroma, as we recognize it in coffee comes from the roasting process. The green coffee beans whose smells surrounded me in those tubs at Compass were grassy and fruity. They were vegetal. Roasted coffee is warm and inviting and savory. And, while it’s true that roasting is key, those enticing aromas don’t come from nowhere. They are the fragments and re-juxtapositions of molecules that are present in the green coffee.

Naturally, then, what those molecules are, and their origins, are critical to what the bean will become. There are some differences between Arabica (Coffea arabica) and Robusta (Coffea canephora), some important ones being that Arabica has more fats and sugars and Robusta has more caffeine. And, certainly some differences come from terrior. That saying, “you are what you eat,” is just as valid for plants as it is for us humans. The mineral and nutrient content of the soil where the coffee tree grows results in differences that we can absolutely detect. But what interests me more is another aspect of terrior that s...