WHAT DOES COFFEE do to you? Dinah Lenney’s Coffee is a free-form exploration of such surprisingly complicated questions: Why do we drink coffee? What gives it its power? Humans have been considering these and other coffee-related queries (like “Is it good for my health?” and “Is it good for my society?”) for centuries, ever since they first encountered the substance. Lenney is most interested in coffee’s direct effects on our lived experience, and what they mean.

The active property of coffee is called caffeine, as we all know. The word for the compound was coined in 1830, as a result of research by two different groups of scientists — one in Jena, Germany, led by a young chemist Ferdinand Runge, and the other in France, led by Pierre Jean Robiquet and Pierre Joseph Pelletier. Both groups successfully isolated the active substance of coffee in an organic “base” or vegetable salt. They showed that this salt caused the effects associated with coffee in humans. Caffeine, in other words, is the drug, and coffee is its vehicle. In 1861, Adolph Strecker defined the molecular structure of caffeine in the formula C8H10N4O2. Caffeine isn’t everything, though: coffee still tastes reasonably like coffee without caffeine, and coffee’s distinctive flavors, we now think, reside in a different set of chemical substances, including aromatic oils and volatile flavonoids, most of which are produced during the pyrolytic roasting process.

Yet isolating caffeine freed humans to think about what coffee does as a drug. Caffeine is similar to other psychoactive vegetable salts in tea, chocolate, and a few other products, like guarana. Caffeine, we now know, interferes with the process in the brain that makes us feel tired. It alters the brain chemistry of sleepiness. As we grow fatigued, our brain creates a substance called adenosine, which binds to adenosine receptors, causing drowsiness by slowing down the brain’s cell activity. Caffeine confuses this system, as it can also bind to adenosine receptors. As a result, the brain is fooled into thinking it isn’t as tired as it is. This also causes the body to release adrenaline, which makes you feel more excited. Caffeine doesn’t wake you up, but it does stop you from feeling so sluggish. In 1674, when the English natural philosopher Thomas Willis was analyzing the effects of coffee, he said it was an anti-hypnotic, “highly efficacious for the driving away the Narcosis or stupyfyingness.” Although caffeine can make you feel less drowsy, recent research also suggests that it doesn’t make you think more clearly, or be more creative. But maybe, as Lenney shows, that doesn’t mean coffee doesn’t do that. Coffee, she suggests, is more than just caffeine, more than just a chemical. Rather than simply the operation of a drug on brain chemistry, Lenney shows how coffee is better regarded as a complex human or cultural product, which comes packed with all sorts of memories, associations, and behaviors. The greatest contribution of Lenney’s fine “object lesson” on coffee is to remind us of just how varied and idiosyncratic most of those associations and memories are. Coffee remakes each of us in distinctive ways. And it also helps us make up a mental picture of others, as in this passage about Lenney’s father:

I don’t remember how my father took his coffee, not really, but I want to think he drank it black — of course he did. Who to ask? Nobody to ask. Nobody to ask about my father and his coffee —

Well, let me try to remember — am I making this up? — so strong is my sense of his presence, his voice, I can hear it still, coming from the kitchen, where he talked on the phone; and read the paper; and drank his coffee — his black coffee —

Or from the patio, where he lounged, sunning himself — talking on the phone; reading the paper; drinking coffee, more coffee, definitely black —

And I remember him taking me out to lunch, watching me eat, a grilled cheese sandwich every time — with potato chips or French fries or onion rings (all forbidden foods at home) — and a milkshake or a frappe. If he ate, too, but usually he didn’t, but if he did, say, order a tuna on rye, it went down in two bites, I swear, just two. Then: Coffee, he’d say to the waitress. Cream? she’d ask, glancing up from her pad. Because his voice was so deep? Because he was handsome and monosyllabic?

Black, he’d say again, without looking at her. Black, for sure, no question about it, I knew it, I did. And — this I also know — he never said please. Or thank you. Only, Coffee, black.

As every coffee drinker knows, coffee is also highly addictive. In fact, people have described it as the most addictive psychoactive substance, partly because the majority of humans are very tolerant of the effects it has on us. The drug is powerful, and has diverse effects on different people — we probably all know someone who doesn’t get along with it, as well as many others who can’t function without it. According to the American Psychiatric Association’s handbook, the Diagnostic and Statistical Manual of Mental Disorders (1994), after five or more cups of coffee, drinkers can expect to see restlessness, nervousness, excitement, insomnia, flushed face, and a rambling flow of thought and speech. But thinking about coffee as a drug, Lenny reminds us, is only one way to ponder its substance. One of the more recent alternative approaches is to think of coffee as an active agent in its own fortunes in the great competition for existence. Coffee is a plant that used to live in a relatively small corner of the globe, Ethiopia, but is now cultivated and consumed the world over. It has colonized humans, and induced them to produce it in huge quantities. As one financial meme has it, coffee is the second most valuable globally traded commodity in the world, after oil. This too Lenney touches upon.

Lenney’s book, part of the publisher’s Object Lessons series about the “hidden lives of ordinary things,” is a fluid, involving memoir of her experience of coffee, a pleasurable tour of her memories, reflections, and research on the topic. She has clearly put in the work of learning about coffee in the course of writing this book, but she wears her knowledge in a gently non-scientific way. The result is a winning combination of enthusiasm and naïveté, which allows the reader to explore recent research about coffee and its physiological effects, the more esoteric corners of coffee connoisseurship and fandom, and the cultural attitudes to coffee shown by her friends and family without ever feeling lectured. There is as much talk of “Chock full o’Nuts” as of the terroir of “single-origin pour-over,” along with explanations of what those phrases, and ones like them, mean — which comes in handy for readers unfamiliar with American mass-market coffee brands and hip coffeehouse jargon. And refreshingly, Lenney is a skeptic about the wilder shores of coffee fetishism: she’s interested in new experiences, but also knows that she loves the drink in all sorts of ways, not just the latest and most esoteric.

It is probably true that the book could be more aware of its cultural parameters. It is set in Los Angeles, and also incorporates Lenney’s New York Jewish cultural background, yet she could have reflected more on the cultural specificity of her story: coffee-nuts, after all, come in all shapes and sizes, towing all sorts of experiences. Nonetheless, this deft memoir-cum-meditation is as savory and stimulating as its subject.

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Markman Ellis is professor of 18th-century studies in the Department of English at Queen Mary University of London. He is the author of The Coffee-House: A Cultural History (2004) and editor of Eighteenth Century Coffee-House Culture (2006).