Science: Diner coffee is terrible

CHICAGO — Tim Taylor, a founding partner of Ipsento Coffee, lifts a mug of coffee to his nose. “Smells like a wet brown paper bag,” he says.

We are not, I should add, at Ipsento, which is one of Chicago’s best coffee shops. Instead, we are sitting across from each other in one of those snug, well-cushioned booths at a diner (that will remain unnamed). You know, the kind of establishment that serves limitless coffee in thick, heavy mugs. On the side is an abundance of creamer cups, way more than any one person would ever need, along with a tall shaker of sugar.

Even though I’m practiced in pour-over and own a digital scale solely for weighing beans (by the gram) for my morning pot of French press, when someone mentions coffee, diner coffee immediately pops up in my head. I know I’m not the only one. There’s something so quintessentially American about sitting in a diner, coffee mug in hand. Can’t you just picture the waitress gliding through the room with a fresh pot, ready to top you off?

Then I decided to actually visit some diners in Chicago. It did not go to plan.

Back at the undisclosed diner, Taylor scribbles down some equations on a piece of paper, trying to calculate the strength of the coffee. He estimates the size of each pot, and then asks the waitress how much ground coffee they use for each batch. After working the problem out, he stares at the paper. “There’s no way this is right,” he says, scratching his head. “It’s way too low.”

He then breaks out a refractometer, a device that measures the total dissolved solids in water, a helpful tool for figuring out the strength of a cup of coffee. He picks up what looks like a medicine dropper, sucks up a small portion of coffee and then squeezes a drop onto the refractometer’s lens. Seconds later he has a reading. “Well,” he pauses. “I was right.”

There’s no doubt: This diner serves extremely weak coffee. The total dissolved solids for the cup is 0.78 percent, which is dramatically lower than any official coffee agency recommends, including the National Coffee Association (which recommends 1.30 to 1.55 percent) and the Specialty Coffee Association of America (1.15 to 1.35 percent). According to Taylor, Ipsento aims for about 1.37 percent, which is nearly twice as much. In fact, the diner coffee’s reading is so low, it’s off the brew chart that Taylor brought for reference.

Turns out, lots of diners serve weak coffee. How else do you think they can afford to endlessly refill those mugs? But after a few weeks of diner hopping, I also came to the conclusion that most diner coffee isn’t just weak, it’s bad. With a few notable exceptions, I could barely finish a cup. I encountered coffee that was achingly bitter, aggressively smoky and somehow still watery. Some sips stung with an astringency that left my tongue oddly dry.

This doesn’t come as much of a surprise to Aaron Campos, the director of coffee and roasting operations at Dark Matter Coffee. “I think it’s interesting that you are worried about the strength,” says Campos. “When you’re looking at diner coffee, you’re looking at very bad coffee (beans). It doesn’t matter if you dose it correctly.”

Campos notes that most diners buy the cheapest coffee possible from roasters who buy the lowest-quality coffee beans. To create a more consistent product, these roasters often over-roast the beans, which can introduce off flavors.

Bitter dregs

But even if a diner purchases high-quality coffee, so much can still go wrong, says Taylor: “Equipment also factors in. Are they changing the water filter in the appropriate amount of time? Do they clean the equipment? Some places never use soap and water to clean the (coffee) machine. Then rancid oil will build up from the coffee beans, and it will not improve the cup.”

I know what you’re going to say. I’m a snob. I’m picking on coffee for the working man and woman who can’t afford to go to those expensive and pretentious hipster coffee shops.

But most diner coffee isn’t even cheap. That cup at the undisclosed diner was $2.99, and you only get free refills if you purchase a meal, most of which are more than $10. If you want a cup to go, you pay $3.19 for 12 ounces. A standard drip at Ipsento 606 only costs $3.03. While only 8 ounces, it’s also not watered down.

Worried that I was being overly critical, I even swung by a Dunkin’ Donuts to see how the chain’s coffee stacked up. I took one sip, and after a morning drinking diner brew, it felt like an angel had descended from on high to personally kiss the foam cup.

It hurts to trash diner coffee, because I’m a sucker for basically everything else about the concept. As I traveled around town, I feasted on piles of crispy golden hash browns and flaky biscuits covered with creamy sausage gravy. I dug into puffy pancakes the size of dinner plates and toast slathered with jam. I soaked in the kind of unpretentious and welcoming atmosphere that new restaurants would pay serious money to replicate. I was called honey and darling, and not in an ironic way. I just didn’t like the coffee.