Instant Genius - How to perfect your coffee routine

Episode Date: February 5, 2024

Coffee is a drink favoured by billions of people around the world, but doing it right isn't easy.  We spoke to Christopher Hendon, a computational materials chemist and coffee expert from the University of Oregon.  He talks us through how to make great coffee at home, where to spend your money, and debunks the myths of the coffee world. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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For many, coffee is a daily part of their lives, whether it's a necessity to get going in the morning or simply an enjoyed ritual. There are billions of coffee drinkers around the world. How much do we really know about coffee? How can you make a fantastic cup at home? And what are the answers to the many myths that surround it? We spoke to Christopher Hendon, a computational materials chemist, an international coffee expert, to find out.

So this is something that you and I have spoken about before around this idea of, you know, how do you make the perfect coffee? And as you quite rightfully explained to me, there is no such thing as perfect coffee. But could you, I guess, talk us through the steps to how someone makes a good cup of coffee or one that's going to taste better than the average? So the most important thing with brewing excellent coffee is starting out with high-quality coffee beans themselves. There's not really a consensus as to whether a dark roast or a light roast is better. In fact, we leave that open to your preference.

Instead, what we tend to care about in the industry is how long it's been aging since it was picked as a green product. So, you know, fresher crops typically taste better. And then how long since it's been roasted? And now if you drink coffee too close to roast, it tends to not taste that good. But if you drink it too far off roast, so if you wait too long, it can seemingly start to taste like it's lost a lot of the volatiles that we like. Together, those contribute to what I call bean quality. And that would be probably about 50% of the scientific importance that goes into a cup. Then next, I would say probably is water chemistry. And if you don't control for this in the sense that you just use the same water in your house every day, then you're actually going to be pretty consistent with the water chemistry. It does fluctuate over the seasons because of different rainfall and so forth. But the general idea is that the water chemistry is going to dictate the flavors that you can taste.

The most important being hard water makes acid imperceivable. So you won't be able to taste very bright flavors. And then after water quality, I think, is where brew method and brew apparatus come in. I'm going to lump all of them together, but simply state here that the most important thing you could spend money on. The most important aspect of brewing coffee at high quality is using a grinder, which produces particle sizes, where the biggest piece and the little piece that come out of it are close to the same size. And the typical poor performing grinders, like the whirly blade grinder where you push down, and you might have seen one of those in your

kitchen, for example, those grinders tend to do a bad job. And when you end up with a really small piece and really big pieces, you end up with flavors that are tasting simultaneously really heavy, perhaps even dark, if you want to call it that, maybe a little skunky, while also not getting the clarity of the front end, the acids and the sweetness that you'd hope for. So all of that together, what gives rise to an excellent cup of coffee then is if you can control for each one of those things, so if you know how old the coffee is, if you know that your grinder's performing consistently and you know your brew water is at least not changing that much and you're happy with it, then simply achieving reproducibility that you're happy with is good. But if you want to try and elevate

your coffee experience in some way, or at least change it somehow, one thing you could do is go through each of those variables and change them. So, for example, you could try buying different coffee from different origins or roasters. You could try grinding the coffee on a different grinder. Now, that's a little more challenging because you know, you might have to either do it in a store or buy something. And then in terms of water chemistry, that's probably the most rewarding experiment do because you can simply buy bottled waters and they tell you the mineral composition. And I would recommend people try that experiment, you know, take a really soft water and take a hard water. The easiest hard water defines probably Evian. You put those with coffee, you're going

to taste a major difference. So you fiddle around until you find something you like. There's not really a scientific definition of absolute coffee quality in the sense that my group does not necessarily know what makes excellence. We just have our own preferences and we try and achieve them every single time we make cotton. So if someone's looking to, I guess, improve the home setup that they have, a good grinder is, I guess, more important than, let's say, some of us looking at different coffee machines and maybe wants to get an all-in-one system. Absolutely. So the grinder is the most important step in the technology brewing side. You can then add hot water, cold water, to your coffee however you please. And of course, you arrive at different flavor profiles,

a cafetire or French press is going to give rise to a thicker cup because the fine particles are still in the cup. It's a full immersion brewing system. And if you like that, excellent. They're cheap. On the other hand, you might like something a little more complicated like an espresso. And if you start to wade into the world of espresso, it is a challenging and expensive place to start to enjoy coffee. But at the same time, the grinder is still the most important piece there because you have to be able to grind sufficiently fine to make espresso. So I think the industry is converging to this idea that if you were going to spend any money on coffee equipment, the piece that you would spend it on is probably the grinder. And you kind of touched

it a little bit there, but once you've ground your coffee and you get to that stage of actually making it, there's loads of different sort of brewing methods that are available. Is there one that's better than another? Again, is this just another sort of way to put your preferences out there and change coffee to how you like it? So the brew method needs to match the particle size distribution that comes out of your grinder. And so there are actually better brew methods for cheap grinders. Let me give you an example. If you don't have a grinder that produces a really consistent particle size, you're going to really struggle to make excellent tasting espresso. Pourovers actually become a little difficult as well. And in fact, the easiest brew method for a

sort of lower end grinder is actually a full immersion where all the water touches all the coffee. There are a couple of examples of that. One is the French press, as we mentioned. But the next one is the arrow press, which is basically a French press, but allows you to force the water out through a filter paper rather than a mesh screen. Both of those do really well if you're not really able to control the particle size distribution carefully. And then once you are able to control that particle size distribution with a different grinder perhaps, then you can start to imagine that actually, sure, the French press and arrowpress still do an excellent job. But you also open up the opportunities for other methods like pourovers and even espresso, if you. you've got the equipment for that. So we're talking about this from the angle of a lot of people that are trying to get the absolute best taste out of coffee and they're drinking coffee,

I guess the taste and the enjoyment of it. But there's a lot of people where coffee is more just, I guess, to boost in energy. You know, that's all it is to some people. Is this the best option for people that want that? Or would someone be better off with, you know, drinking tea, water, energy drink, something of that nature if coffee is just a stimulant to them? Yeah, that's a tricky question because I think people are aware that there are plenty of sources of caffeine that they could source in other beverages outside of coffee. But coffee seems to be prevalent because not only does it have caffeine, but also people like it. So I don't really know whether there's a better option in the sense that we tend to like the coffee and we tend to have our own flavor

preferences. And I cannot really imagine replacing my morning routine of having this cup of coffee that I'm having now with a glass of water or a soda or something, right? It's something that has caffeine in a tea, maybe. Okay, I understand the tea is, you know, of course, something that a lot of people like, but I don't think it's really a substitute. I think it's a different thing than coffee. But I should go back to a underlying point here, which is this idea that coffee is a stimulant and how do we actually access that?

Well, of course, we're relying on the caffeine that is contained within the beans. And so paramount to being able to have that stimulant effect is to be able to extract the caffeine. And one of the misconceptions in the coffee industry is basically that the brew method doesn't really matter. You end up with caffeine in your cup independent of how you brewed it, maybe a little more or a little less. People tend to think it depends on the beans you've used, or rather whether it's light or dark. And really, there's not very much evidence to suggest that that's true because the caffeine is produced by the plant. So once you start roasting the coffee, you start destroying some of that caffeine in the roaster. And so you'd think then, okay, so darker roast

coffees have less caffeine, but they don't really because you also still need to extract it. And so the darker the roast of the coffee, the less dense the coffee becomes. And so the more accessible it is to water. And so as a result, it's a bit tricky to discuss the stimulant effects of coffee because it does depend on the coffee. You know, light and dark roast of the same coffee, you're going to have more or less the same caffeine accessible. Two different coffees from different origins will have wildly different content.

And so, you know, if you're seeking a high amount of caffeine, you may actually be better off changing the coffee you're having to something that contains a bit more rather than seeking other beverages. And does that also change for people that are going to a supermarket and buying, let's say, pre-ground coffee? Is there certain brands that will be more caffeinated or even does the pre-ground stuff tend to have less caffeine than if you're grinding it yourself? So the grinding process does not lose an appreciable amount of caffeine. So it's not the fact that it's pre-ground, but it's more likely related to how much of that coffee is robusta rather than arabica. Typically for these pre-ground coffees that you'll find perhaps in the supermarkets,

there is a bit of robust in there. And the more robustly you have, the more caffeine you're going to have because the plant produces a lot more than arabica. The problem with this, though, is it's hard to know exactly what's in a coffee blend. I mean, I can't do it. I can't tell from just looking at it. So unless it's written on the label or something, but I'd simply say that you've got to find something that you think tastes good. And caffeine itself is extremely bitter. So if you can tolerate a large amount of bitterness, then you're probably going to enjoy a higher caffeine content coffee. Bonjour, compadre.

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and unforgettable listening experiences at home. Try it for yourself at a focal powered by name boutique. Visit focal powered by name.com for more information. And coffee is drank by such a large group of people, but does coffee have the same effect on, I guess, everyone? If, for say, there's someone who's older drinking coffee, does it change in that sense? Well, the human body does undergo some changes as it ages,

but it's not as dramatic as no longer being able to respond to caffeine or perhaps responding in a different way. I'm not a medical doctor in that sense, so I won't be able to fully provide a good scientific basis for this, but I'll simply speak about myself and say that I don't really feel the energizing effects of caffeine anymore after running a coffee lab. I taste a lot of coffee throughout the day, and I feel like perhaps I've become immune to it.

I also don't rely on it. In the morning, I don't have a headache when I don't have coffee. And so in that sense, I do think that there's pretty significant differences between how people respond to coffee, where, you know, my wife really sees that energizing effect, and I basically just enjoy the fact that's hot and taste acidic. And so with that in mind, I don't really know how you can ask me the same question 30 years from now, and I'll tell you if my body's changed it all. Use me as an n-equals one experiment. That's good. All right. I'll come back to you for that then. Yeah. So I wanted to do, I guess,

a bit of myth-busting. There's, you know, all of these beliefs around coffee that might be true, might not be true, but I think they're quite often quoted. So I've got a few sort of common ones here. And one of the ones that I've personally heard quite often is this idea of where you store your coffee and a lot of people store it just in the cupboard, but there's this idea that it improves coffee by storing in the fridge or even the freezer. Is there anything to that? Yes. So in 2016, we wrote a paper on the benefits of freezing coffee that is storing it in an airtight vessel in the freezer. It turns out that there are several reasons why you might want to do this. First, coffee is primarily a retro nasal sensory experience where you take a sip and then you feel a lot of the flavors coming through in the back of your tongue and the

back of your nose. And those molecules that tend to give you that experience are what we call volatile or they will evaporate. And so if you store the coffee open to air at any temperature over time, you're going to lose those molecules into the atmosphere. At higher temperatures, you're going to accelerate that process. So storing in a cool, dry place, as you see on labels all the time, is always a good idea for foodstuffs in the sense that you don't want it wet because, you know, you then run a risk of having some sort of biological activity occurring. And you also don't want it hot because you don't want to drive off those volatiles. But then if you put it in the freezer, it turns out the freezer is pretty wet because, you know, it's really high humidity in there.

Part of having your refrigeration system is there's just a lot of water condensed from the atmosphere you're nearby. So you do need to make sure that's airtight. And so one of the ways you could do that is in a jar or perhaps in a resellable zip block bag or something like that. But then the secondary benefit here is that if the coffee is then ground while cold, the coffee seems to undergo a material transition, what we call glass transition, where no longer does it grind as typical coffee would, but instead it now grinds and fractures in a way, kind of like when you see broken glass at a bus stop or something. It's all very regular but small pieces. And as a result, grinding frozen coffee is actually one way to help the grinder

in terms of producing reproducible particle sizes. And so to summarize, it's basically if you store your coffee in the freezer, you're going to get the material benefit of it fracturing more regularly inside your grinder. And also, you're going to have less of the volatiles leaving the coffee. So in principle, prolonging the quality of that coffee. So another, I guess, myth that I often hear is this idea of burnt coffee or coffee tasting burnt, can you burn coffee? Or is this just more a taste that people are experiencing? So the coffee roasting process begins with room temperature coffee that's dropped into a heated drum.

And over time, the coffee will start to turn yellow than brown. And if you roast for a really long time, black. The end temperature for a dark roast coffee is in the vicinity of, I don't know, let's say 220 degrees Celsius. So at that point, you are well above boiling point of water. Obviously, the coffee has started to turn darker color, so you are, in principle, heading towards burning it, but no different to how you'd cook a piece of meat or something, right? Now, why I mentioned the end temperature is because when you brew coffee, you're brewing coffee with an upper limit of 100 degrees Celsius water at one atmosphere of pressure. So in that sense, you're never going to really reheat the coffee beyond the end temperature that generated all of those colors, the dark colors that you see in the

coffee being in the first place. And with that in mind, I'll simply say then that the coffee itself may have come out of the roaster with burnt tasting molecules already contained within the coffee. The brew method allows you to access them should you like them. Evidently, many, many people like that flavor profile because it's so popular. You're going to tend to get some of those more caramelized, dark chocolate, like baker's chocolate notes. And if you try hard, you can access negative flavors in that coffee, but also in all coffees. But you can also access really good flavors in those coffees as well by changing brew parameters that I mentioned earlier. So this phenomenon of talking about burnt flavors can be accessed even with light roast coffees. If you brew

with really, really hot water for a long time, you're going to be able to get some of those burnt flavors out. But if you don't like that developed flavor profile, the darker profile, then main recommendation here is probably just to buy lighter roast coffee. So there's an often quoted bit of research about this idea that we experienced this boosting cortisol between, I think, 8 and 9 a.m. And the argument here is that you shouldn't be drinking coffee within this time because you're already getting a natural energy boost. Is that something that's commonly true to be known with coffee? I'm not aware of this cortisol boost in the morning. We all make decisions about what is good for us and what is not. And if I had to forfeit having coffee in the morning,

because there was an incremental benefit to the human body by doing so, I would say no. I would just rather have the coffee and forego the benefit of having that cortisol bump and not having the coffee. So we all make our own decisions in that sense. I think the one piece of evidence that really supports coffee consumption and maybe this cortisol bump is sort of just part of the fluctuation of sort of in the noise, if you like, for human health, is that very few products on Earth are consumed as widely as regularly as coffee. And there are ample amounts of populations that could do the control experiment of not having it at 8 a.m. and seeing some benefit. I'm not aware of the research that's done it or not, but I'll simply say that we are continuing

to live a very long time. And I've definitely never heard of the average person not drinking coffee but life expectancy going up. So at some point you got to make a decision. If you think it's bad for you, then don't do it. But most people tend to like it. I guess on that similar topic, is there any kind of links between coffee and your health? Or is this typically, as you're saying, we've drank so much of it now and so many people drink so much that it's pretty non-existent? So every year, there are a series of scientific publications that come out, one that will tout the benefits of drinking coffee. And another one will say that there's problems with drinking it. And they go back and forth, but they're usually based on a couple of chemical concepts that, you know,

coffee is filled with phenolic compounds. Phenolic compounds are antioxidants in the sense that when you drink them, your body will not oxidize. The molecules you've consumed will. Therefore, you're not going to undergo rust, okay, human rust, if you want to think of it like that. basically almost everything you eat is an antioxidant. So it's not surprising to have coffee fall in the category of being good for your health. And then inevitably, someone will publish a paper that says, oh, well, it's roasted. And during the roasting process, it will generate a molecule known as acrylamide. And acrylamide undergoes epoxidation and can then, in principle, interfere with your DNA and cause all sorts of problems. And this is actually referring back to a very famous paper that was published in

nature many years ago now that basically argued that anything that have featured acrylamide, which is everything that's ever been cooked, basically, that was a live one. So plants or animals could create this molecule, which could in principle cause cancer. Now, everyone goes back and forth on this. And I'll simply just say then that you need to have a lot of one particular molecule for it to be beneficial or detrimental to your health. And when you're drinking one to five cups of coffee in a day, you're not going to get a lot of any particular molecule besides caffeine and chlorogenic acid. And it's not the molecules that are responsible for causing cancer. I mean, chlorogenic acid's phenolic, but that's not really going to make a market difference in antioxidant uptake. So all of this is to say

every year we go back and forth as to whether it's good or bad for you. As with all science, I could be totally wrong about this in three weeks. weeks when a next paper comes out and says something about how excellent or bad coffee is for you, but right now I'll just say it's a wash. It's something that we like to do and everything that you put in your body comes with some risk and we all choose to take their risk when it comes to eating and drinking things. And for me, coffee doesn't fall in a high risk category. So as someone that has spent so much of your life researching coffee, drinking coffee, understanding it, is there anything about it that stands out to you something that is truly significant about this?

thing that we all do. Yeah, so coffee is one of the only beverages that requires the end user to actually make it. You know, unlike wine where I'll pull the cork out or twist the cap or with beer all open the lid and milk, you just simply open the carton. Coffee does require the step of grinding and then adding water either hot or colds than filtering somehow. And maybe you choose to not filter and maybe you choose to use different water temperatures. Maybe you make decisions throughout the process. But the point is you don't get to make those decisions for the other beverages. You have to make them for brewing coffee. So I do think that coffee is actually a sort of a gateway to the scientific process because there's a lot of variables and you get to control them and see how they impact the beverages flavor in the end. Now, this isn't all that different to tea. I mean, in brewing tea, you can control how much tea you put in, how much of the dry material you put in, how much water you put in, and the temperature and then steep time.

And those are really the four parameters for tea. It's not really that different for coffee. except for we have that grinding step, which I mentioned is probably the most important step in the technological side of things. And so when you're thinking about is coffee unique, I'd say coffee and tea together are unique in that they require the end user to actually make it. And that's really quite dissimilar to all of these other products that we tend to drink. I mean, as you just mentioned there, there's this long list of variables, whether it's the grind, the method of brewing, length of time, and water, all of these different factors, it allows for a lot of experimentation with coffee and how we make it. Do you think we'll be drinking coffee in a fundamentally, I guess, different way in the

future? Or do you think this is just kind of, we've hit what it is and we'll just keep enjoying it for what it is? So coffee is a crop that is susceptible to fluctuations in growing temperatures and moisture availability. And actually, I want to cite some excellent work from Aaron Davis, who's at the Royal Botanic Gardens Q, who's been studying how coffee is cultivated and its susceptibility to climate change. And in several of his papers, he has shown that we're expecting a reduction

in crop viability in producing regions such as Ethiopia and other places by up to 80% in as soon as 50 years. What I'm really trying to say is that we're not going to have as much coffee as we have right now later in our lives. And that means that there is going to be a focus on somehow either growing new types of coffee that are resilient to drought and perhaps whatever

the climate is in these producing regions. It also points this idea that perhaps coffee is not as sustainable, at least in its current embodiment, whether that's because we're not good at extracting from it. You know, when we brew it, there's still a lot of material left over that we put in the trash. And whether that material is tasty or not as a different problem, but from a mass perspective, we're only using about 20% of the raw product that we've actually obtained. So there's obviously an opportunity there. With those parameters considered, I would say that we are definitely going to be tasting new flavors in the future, whether they're better or worse, and exploring more sustainable

brewing paradigms, as well as producing paradigms. Because the crop itself is highly susceptible to climate change, and the scientific literature is pointing strongly towards the fact that coffee will be reducing in quantity in the coming years. Thank you for listening to this episode of Instant Genius. That was Christopher Hendon talking about coffee. The Instant Genius podcast is brought to you by the team behind BBC Science Focus magazine, which you can find on sale now in supermarkets and newsagents, as well as on your preferred app store. Alternatively, you can come and find us online at ScienceFocus.com. This podcast is sponsored by Name, Audio and Focal.

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