There is a lot that goes into a cup a coffee. From beans, to roast, to grind, to water and even temperature, it is incredibly difficult to make one cup of coffee the exact same as the next. But researchers at the University of Oregon may have found a way to make a cup of coffee more consistent. Chris Hendon is a chemist and associate professor at UO. His previous research illuminated how spraying water on coffee beans before grinding saves on waste and makes the espresso shots more consistent. Hendon joins us to share more about his work and the world of coffee.
Note: The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.
Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. Coffee has been giving people a buzz for hundreds of years. Maybe it’s time that we returned the favor. Researchers at the University of Oregon say that an electrical charge can help producers create a more consistent cup of coffee. It’s just the latest finding from a coffee-focused lab at the [University of Oregon] that has already published research on freezing coffee and spraying water on beans before they are ground.
Chris Hendon runs the Oregon Coffee Lab. He is a chemist and associate professor at UO and he joins us now. It’s great to have you on Think Out Loud.
Chris Hendon: It’s my pleasure.
Miller: I’ve read that you did not set out to become a scientist who focuses, among other things, on coffee. How did it happen?
Hendon: Yeah, well I was definitely not hired at the University of Oregon to study coffee, that’s for sure [laughs]. Back when I was a grad student in England, I took an interest in it because I was drinking a lot of it to get through grad school. Inevitably, I took a fascination, or maybe even a scientific interest, in the variability that happens when you go to a cafe one day and it tastes great and the next day it tastes different.
So over the years, I started studying it. Eventually, we started writing grant proposals. And when you get the money, you’ve got to do the work. So that’s what happened over COVID, and here we are.
Miller: Coffee is one of the most popular drinks on the planet with, in my mind, some very super nerdy preparers and drinkers. I would have thought that it was the kind of thing that people had already approached in a rigorous way – at least some people, in a rigorous or even scientific way. Is that wrong?
Hendon: You’re absolutely right. It’s a deep rabbit hole. But everybody draws a line with everything they do to the extent in which they want to study it. So for example, you and I might like eating steak, but we don’t necessarily know everything that goes into producing that steak, right? So with coffee, the problem is that you can get fascinated about the agricultural practices and maybe know a little bit about flavors that come from certain origins. Or perhaps you might even have invested in an expensive grinder or understood water chemistry. You get the idea. I can start layering up the levels of complexity, and at some point, it’s easier just to grind the beans, and pour water on it, and make the drink and drink it, and accept the variability.
The problem, however, is that the industry – as you mentioned – is extremely large, and variability is the curse of a large industry. You do not want to have one drink that tastes excellent one day, and you go back to the same brand and it tastes different the next day. This is a bad thing. So there’s a huge financial motivation to study this. There’s also the societal implication of just having a nice coffee. We sort of fall in between those two different zones.
Miller: I mentioned the electrical charge, which is one of your recent studies. Can you describe, first of all, what you set out to try to figure out?
Hendon: Back in COVID, we were funded to basically develop a method of measuring what is dissolved in a cup of coffee. The intention was never to make a better cup, but rather understand: If you like this cup, why? It’s actually quite a challenging chemical problem to parse flavor at that level of fidelity. But it’s even more challenging in coffee, because if I brew the coffee and you brew it, we’re probably gonna end up with different tasting cups. So there’s these compounding variables.
We were funded initially to basically understand which variables dictate the chemical composition of a drink. Along the way, we were realizing that we were struggling with reproducibility. I’d make one shot of espresso today, and later on, I’d make the same thing and it would taste wildly different. And indeed, the chemical analyses were revealing the same differences.
Miller: With the same beans and the same espresso maker? I mean that most of the variables were controlled for and yet it would actually taste appreciably different?
Hendon: Right, exactly. This is one of the challenges. Because it’s easy for us to attribute this to the barista. And I certainly have flaws when it comes to making coffee. I’m not a trained barista that you might find in a local cafe. However, I am a scientist. I’m pretty good at following recipes, and I understand how to use my hands and so forth. But the reality is, it’s just water, which is going to take the path of least resistance. And you’re grinding something up really small, and there’s changes in humidity, and changes in the moisture in the bean and the temperature of the beans throughout the day.
All these things result in water traversing through that puck of coffee in a different way each time. And on average, maybe they’re the same. But between each shot, they’re quite different. So there wasn’t a fast way to measure the composition.
I’m going back to your original question about this electricity thing. The basic premise here is that molecules will react with an applied electrical charge, and different molecules will do so at different voltages. So I can measure how much caffeine is in [a] solution separately from how much acid is in [a] solution, by simply looking at different voltage regimes. And if I want to then understand flavor, perhaps I don’t know what the acids and caffeine taste like independently. But I can start to build this map, if you like, of if the caffeine exists in this concentration and the acids in that concentration, then we’re going to start to see some flavors emerge that are common between coffees. We can make some broad statements about, this tasting darker than that or this tastes more bitter than that.
Miller: And the electrical charge machine helps you sort of map out the components of the various liquids?
Hendon: Right. Basically, the different voltages select for different molecules, and then the amount of current that passes tells you how many of them there are. So if you and I were to prepare the same cup of coffee and do our very best to do exactly the same thing, this system, which is basically just a multimeter running in reverse – instead of measuring voltage, it’s applying it – it’s going to tell us, as we scan across different voltages, where there are differences in composition. So if we made the same cup, they would have the same signal. If we have a different composition, then you’re gonna see that reflected as a different signal.
Miller: This is interesting because it seems like what you’re saying is the point of this is not some scientific analysis of quality: This is a good cup, this is a bad cup. It’s more looking for similarity: This is a kind of a picture of this cup, and if you like that one, we actually make it easier for you to say this next cup is actually more or less the same. As opposed to saying, this is the best cup, so let’s all make versions of the best cup?
Hendon: You’ve captured a few talking points there. So the first thing is my lab’s never ever tried to tell people what is good and bad. Most of the work we do is thinking about ways in which we can measure what has occurred, and then you can still taste it and tell me whether you like that or not. Then we have all these techniques to basically arrive at that same flavor again.
So that’s item one. But item two, you’re highlighting an application of this, which is thinking about cup-to-cup variation. But I’ll give you a more macroscopic example of this. Every year, large companies – Starbucks, illy, whomever – are trying to create blends that taste the same as they did last year, but the crop that they’re harvesting each year is different.
So they’re sourcing coffees from all around the world to try and arrive at this consistent flavor profile. They roasted it however they do. How do you know whether it tastes the same as last year? You could use the human tongue. But of course, then there would be coffee that was a year old on the table, and that probably wouldn’t be a good reflection of what it tasted like last year. This device allows you to make a very high fidelity measurement of whether the blend is now having roughly the same flavor profile as the year before.
Miller: Am I right? In the past, they would have used some kind of master taster, people who are trusted to be stewards of a particular company’s flavor? We just give it to Jane. Jane knows our coffee and if Jane likes it, then it’s good to go?
Hendon: You’re exactly right. So every company that has ever produced coffee has Jane hiding behind the bag. This person or people are solely responsible for conveying the flavor profile that matches the brand. This is something that we probably don’t talk about enough in the industry, but it is a select few mouths that are imparting the roast profile and then, terminally, what you think of that brand of coffee’s flavor profile. It really isn’t actually as much about your preferences as it is about their preference.
So that’s why there is differences between the same coffee roasted by two different people. [It] will taste wildly different because the people who arrived at those recipes have different preferences.
Miller: I mentioned some of your earlier findings just briefly, but it’s worth going back to them. What did you learn about freezing coffee beans?
Hendon: That was a paper we published back in 2016, but ended up having a profound impact in the real world. So for example, if you’re in Portland, Oregon, you can go to Proud Mary Cafe and see freezers mounted behind the bar on the wall, and that’s coffee that is frozen before it is ground. The reason that they are doing this is because when you freeze coffee, the little tiny dust that is formed – which the industry calls fines – become more of the same size. So as you have more particles that are more of the same size, the water that contacts this bed of coffee will traverse through it more evenly, resulting in both higher extractions – so more efficient extraction – but also more consistent flavor profile.
You’d think it’s a really small difference, but it’s kind of like the analogy of when you crack your windshield on your car, versus the bus stop [that] gets cracked and shatters into those tiny little pieces. Basically, you want coffee to break into the consistently small pieces. So that’s what freezing does. You cool the coffee down and it all of a sudden starts fracturing more regularly.
Miller: You’re saying that people in Portland can see the results of this scientific academic finding in real life. It was adopted by at least one roaster. How common is it these days?
Hendon: Actually, as with most of my work, it’s probably more common than the cafes are revealing because I think many listeners right now probably keep their coffee in the freezer, and pull it out and grind it, and then put it back in the freezer. That’s more or less what we’re advocating for, to get the material advantage. We kind of just put the scientific firepower behind it to explain why it works so well.
Miller: The thinking is maybe different, too. I mean, if people have done that for years, my assumption is that they think it’ll keep longer. You’re saying that the grind is actually better physically. Different reasons to do the same thing?
Hendon: Yeah, you do get a prolonged shelf life because when you cool something down, the rate of off-gassing and staling goes much, much slower. But the material difference is sort of the secret here.
Miller: What about adding water before grinding?
Hendon: This was actually a stepping stone paper to help us do the electrochemistry thing we talked about earlier. But basically, we realized that every time we’d pull a shot of espresso, we’d have to grind really, really fine. In doing so, you create a tremendous amount of static electricity because the coffee is rubbing on the burrs of the grinder. And those are different materials, the same way that your hair is different from a balloon. So when you rub them together, static forms. That static results in coffee particles sticking together to form clumps. If you’re trying to make a small particle, but instead you make a clump, you’ve failed at making a small particle and now the water is going to go around the clump, rather than touching all of it.
We realized that part of the reason we were having shot-to-shot variation, which I mentioned before, is because there was just static accumulation, which is somewhat of a random process. And as a result, we’re getting these clumps. It turns out that you can turn off static accumulation by squirting one drop of water, just a single drop, on 20g of coffee – the amount of coffee you’d use in a standard single cup preparation, for example.
As you do that before you grind the coffee, the water seems to entirely passivate the charging process. So the benefit of this is you don’t get the clumps, sure. But a more realistic benefit of this is because there’s no static, when you grind coffee in your kitchen, it won’t go everywhere. It just falls like grains of sand on the beach, and goes straight down. So as a result, this research was adopted by many because it keeps your kitchen cleaner and it also helps cafes use coffee more efficiently.
Miller: How much opportunity do consumers – people who are buying already roasted beans – have to make the resulting coffee really good or bad? I guess I’m wondering how much is already baked in, with the way the beans were grown and roasted?
Hendon: You can imagine a pie chart where any of the things in this pie chart can destroy a cup of coffee, but in the hierarchy of what can lift the ceiling of the quality of a cup of coffee, about 50% of that pie chart is coming from how high quality the green coffee is. So if you start with high-quality agricultural product, you’re likely going to have a higher ceiling there. Then the artisan has to turn it from green to brown by roasting, and they’re simultaneously tasting that coffee with their water. So I like to attribute about 20% to the roaster and 20% to the water chemistry. And then finally, that leaves behind 10%, which is the brewing equipment and so forth.
So, I would say that if you buy high quality, freshly roasted beans – these are beans typically that are somewhat expensive, but they’re coming from local roasters near your place – those are already going to satisfy 90% of the ceiling of that quality cup. What you do to it afterwards is sort of out of control, and that’s always been a thorn in the side of the coffee industry. It’s one of the only drinks where the consumer really has to play a role in dictating the outcome. If you have a reasonable grinder and you have hot water, I think you can’t really go that wrong if you just have a consistent routine that you seem to like.
Miller: What do you see as the most common mistakes that people make with their own coffee?
Hendon: Oh, they spend way too much money on equipment and not enough money on thoughtfully sourced coffee, high-quality coffee, locally roasted coffees, and so forth. The reason I say this is because there’s always the next machine that will do something. But at the end of the day, the purpose of brewing coffee is to make big pieces small and then somehow expose them to water.
So if you have a high-quality grinder, like you just buy a grinder that does a good job, and then you can find brew methods, even the most basic one where you don’t even separate the coffee at all ... You just pour hot water in a cup with coffee grounds and you just carefully drink from it so you don’t suck down a whole bunch of coffee grounds. These cups can still be really good, but what makes them good is the high-quality coffee that goes into it. So the biggest mistake is that people will go to warehouse stores and buy kilograms of low-quality coffee, and put it through a high-end machine, expecting good outcomes. When a much better outcome is to go and buy 1 kg of high-quality coffee and put it through, basically, a sock. [Laughter]
Miller: How was your cup of coffee this morning?
Hendon: I’ll tell ya. So, I’m in the lab all the time. So this morning’s cup of coffee was unusually high quality. We were fortunate to receive a gift of a Panamanian Geisha from a close friend. These coffees are typically viewed as some of the best in the world. To give you an idea, it tastes like a bouquet of flowers, like Chanel N°5 but without the alcohol burn. And we had that this morning and enjoyed that. It was wonderful.
Miller: Chris, it was a pleasure talking to you. Thanks very much.
Hendon: My pleasure. Thanks.
Miller: Chris Hendon is a professor of chemistry at the University of Oregon, the director of the Oregon Coffee Lab.
“Think Out Loud®” broadcasts live at noon every day and rebroadcasts at 8 p.m.
If you’d like to comment on any of the topics in this show or suggest a topic of your own, please get in touch with us on Facebook, send an email to thinkoutloud@opb.org, or you can leave a voicemail for us at 503-293-1983.
