Processing, Pt 2 — Drying mistakes that ruin coffee quality

James: This is Filter Stories. I'm James Harper. And we've arrived at the second part of the Coffee Producer Toolkit episode focused on post-harvest processing.

To remind you, this is a series made in collaboration with Lucia Solis to help coffee farmers have a more profitable business. And I think this series will be very valuable for you, because it's hopefully already changing how you see the entire coffee industry. And hopefully this knowledge will shape the rest of your coffee journey, and that will allow you to mould the industry for the better.

So right now we're in the middle of post-harvest processing. Basically, we are looking in detail at the wet mill: what happens once coffee is picked, to when it's sitting in parchment ready to get sent down to the dry mill. In the previous episode, we looked at improvements in coffee picking and the sorting of cherries at the wet mill. And here, we're going to go into more detail into how to better pulp and dry your coffee.

In the next section of the episode, Lucia and I make some recommendations about pulping. So let me explain what that is. You have a coffee cherry, and what you want is the seed inside of it. So, at a minimum, you're probably going to want to remove the coffee cherry skin, and also possibly a lot of the fruit surrounding the parchment. And one of the most common ways of doing that is to run it through a pulper, a pulping machine. A pulper is just basically a set of rolling teeth that exert a little bit of pressure on the cherry, just enough to pop the seed out of the surrounding fruit.

It is a very simple part of the process. And yet Lucia has seen it go wrong many, many times. The first issue is that oftentimes the pulper is set too tight, so as the coffee cherries are going through, in the process of stripping off the fruit, it actually crushes the green seed. And that is just an unnecessary waste. Even if it's only 5% of a harvest that gets crushed, 5% is 5%. And it didn't have to happen.

And the reason this happens is that, you know, a lot of wet mills were built back in the day, like the 70s, the 80s. The machines are still there. So farmers naturally think, hey, if it ain't broke, why fix it? But in this specific case, they get uncalibrated really easily. So if a farmer needs to make an investment somewhere, this is an easy win.

And now here's the second big reason why these need to be replaced if they're really old. A lot of the older machines need a lot of water to do the job — they need water to carry the coffee cherry along and push it through the pulper and onwards. But as we heard in earlier episodes, coffee farmers are now living in a world where rainfall is a lot less reliable. Water is scarcer. Those old pulping machines made sense in a world of abundant rainfall.

Newer pulpers, they use gravity. It's beautifully simple. You build the wet mill much more vertically rather than horizontally, right? So you get your cherries all the way to the top. Then they drop down into the pulper. And then gravity pulls them down through the system. That saves you a tremendous amount of water.

And less water at this stage can also be better for coffee quality. Take, for example, one of the more complex processes: the honey process. Like I mentioned in the last episode, the honey process is where you take the cherry, pulp it, you may ferment it for a little bit — depends, maybe not — and a lot of the coffee flesh is still stuck around the coffee parchment. Now, if you were using one of those old water-based systems, the coffee would arrive onto the patio soaking wet. And with all that water, you introduce a lot of microbes. And so now you have an uncontrolled fermentation happening while the coffee is drying on the patio, producing heaven knows what flavours — and the coffee becomes inconsistent and potentially lower quality.

And so the whole point of this section is: don't reach for the honey process yet. Don't reach for the bioreactor. There is so much low-hanging fruit right here with the basics. So here we go. Pressing play.

James: All right, Lucia. Let's cover depulping, or as you like to say, pulping. We've sorted our coffee cherries. We have all the red ripe cherries in one place. Now we have to remove the coffee flesh from around the seed. How is this done traditionally, and what are some of the problems with it?

Lucia: One of the issues is that the traditional pulpers are designed horizontally. Usually water is what's making the coffee move laterally, which means that you have to use a lot of water to make them work. And the second thing is that many traditional pulpers get uncalibrated really easily.

James: Yeah, that's exactly what was happening with David Velasquez before he upgraded his pulper.

David Velasquez: We used to lose around 15 to 20, sometimes, percentage of the coffee, when we prepared it for naturals, for example. Everything was like, was crushed, and it was like a paste, you know, toothpaste or something like that.

Lucia: So if your pulper is not well calibrated — if it's too tight, then while it's removing the outer layer, it's going to crush your seeds, and then you've already lost the coffee. And if it's too loose, it's not going to remove the outer part, and that is going to be separated out. So you're actually losing coffee because it's still covered in the cascara. So if you have a traditional horizontal disc pulper, they're really hard to calibrate and they're worth replacing.

James: Right. So one of the most straightforward improvements producers can make is to switch to a vertical pulper from a horizontal one, so that gravity, rather than water, is doing the work of actually moving the coffee through the system. It's a simple change that can dramatically cut your water consumption, and it applies to producers both big and small.

For example, when I was in Colombia, I spoke with Jesús Antonio Chala, a producer who works with The Coffee Quest.

Jesús Antonio Chala: Finca El Silencio. Acá una hectárea, es pequeñita.

James: His farm is just one hectare big. The Coffee Quest has community support staff who go out into the fields to help their producer partners improve their farms and their processing. And in this case, what Jesus now has is a vertical system that requires very little water. So his wet mill is built across two floors. The cherries are floated on the top floor. He then feeds the cherries through a hole in the floor, where gravity pulls them down into the pulper below, and from there they go into the fermentation tanks. Almost no water is needed. Gravity makes the whole system flow.

Jesús Antonio Chala: El consumo del agua que se ocupa para esos procesos es muy mínimo.

Lucia: Yeah, I think thisis a really smart method, because by using gravity to move the cherries instead of using water for processing, you also reduce how much waste water you need to treat in the end.

James: Right. And now turning to the larger end of town — for large producers like David from El Salvador, who we heard from just earlier. He had an old mill, and with his old mill he had an outdated demucilager.

David Velasquez: At the beginning, we didn't have a good pulper. It was horizontal — you have to use water for that.

James: He invested in a Pinhalense vertical depulper and demucilager, and the coffees move not with water —

David Velasquez: Pinhalense has elevators.

James: — but with elevators.

David Velasquez: So they elevate the coffees and start dropping.

James: And the water saving for him was enormous.

David Velasquez: And we have like four big tanks, and back in those days we used to use three, at least. Now we use one only.

Lucia: And besides the obvious benefits of water conservation, there's another reason you want to reduce your water usage during pulping. It affects the coffee flavours, and this is especially true for honeys.

James: Yes, David mentioned how in the old system, which was horizontal and used a lot of water, all that water was compromising the quality of his honey process coffees.

David Velasquez: At the beginning, it was so hard to do, for example, honeys — a lot of water. So all the mucilage was wasted, and we couldn't get the sweetness and the mucilage properly to develop good honey processing methods.

Lucia: I want to share a quick note about the honey process. I think the honey process and bioreactors actually have a lot in common. Instead of being the first steps in improving processing, purchasing a bioreactor should be among the last things that you invest in. And when producers who traditionally do washed or natural processes want to experiment, usually they try a honey first.

But in my experience, the honey process is the most challenging. It's like the most difficult part of a washed and a natural. And this is because, just like a washed process, you have to pulp the coffee and you've exposed all of this mucilage. So you have all of this surface area for microbes to feast on this sugary mucilage. But the benefit of a washed process is that it's usually short, so the opportunity for defects is significantly reduced. And on the other side, a honey is like a natural, because it's dried with the mucilage on, and that can make it even slower drying than a natural. So you take the worst part of both of these processes and you jam them together. It's no wonder that so many producers have trouble getting good honeys.

James: So, to wrap up on pulping. Vertical systems use less water, and less water means fewer problems. And if you're still running an old pulper, replace it. Or, at the very least, make sure it's very carefully calibrated every single time you use it.

Lucia: So we covered some options for cherry selection if you can't do it with selective picking in the field. We've talked about ways to reduce water use in the mill by using gravity, and the importance of calibrating your pulper to avoid crushing and damaging coffee seeds.

After pulping, the obvious next step is fermentation. But again, this is such a big topic that it has its own episode, and I can't wait to dig into this one. So for now, we're skipping that step and going straight to a very important but often overlooked critical quality step. And that is drying.

James: Pressing pause. So this next section is on drying, and Lucia sees this as a tremendous opportunity — a place where a producer doesn't have to buy anything new or invest any money. They can just tweak what they're already doing and get big benefits in terms of their quality and the shelf life of the coffee.

Let's cover quickly what drying is. In the wet mill, however you process the coffee — washed, natural, honey — the green seed itself is going to be about 50% moisture. What you have to do is get that down roughly to 11%. 10 to 12% is also acceptable, and some people even have bigger ranges, but for the sake of argument, let's just say 11%.

And I know this sounds like a very specific range. It has to be, because you want to get green coffee down into a stable, low activity state, right? Stable enough that the green coffee, which is still alive — it is a living seed — you want it to be able to survive the journey all the way to the roaster without degrading. If the moisture is higher, you open the door to mould and to defects developing in the coffee. If the moisture is lower, you actually risk the seed dying and becoming very brittle, and so when it goes through the dry mill to get the parchment removed, you risk the beans shattering in the process. And crucially, in the roasting process, you actually need a bit of water, because during roasting the water is what evaporates. And then that begins to interact with the flavour precursors in the green bean to create the coffee flavours we love so much. And again, roughly 11% is a good place for developing fantastic flavours during roasting.

Now, for many farmers, historically speaking, the approach to drying was straightforward: just get the parchment down to 11% moisture, bag it up, and it's ready to leave the farm. How you got there didn't matter. But as Lucia explains, there is so much research coming out now showing that how you dry really matters. This next section runs quite long, because we go into quite a lot of depth there.

Now, I want to quickly also cover that there are different ways you can dry. On very large farms in Latin America, the classic method is patio drying, right? So this is a big concrete space, big enough to play a game of football on. You spread the coffee across the patio and walk up and down, turning it over with rakes.

In Africa, a very common method is raised beds. These are basically where coffee rests on some kind of net. And this is very good for drying, because you get airflow underneath the parchment as well as over the top. And that's helpful, because it gives you more even drying and prevents mould growth. And now, more recently, what you see in Latin America is an evolution of the African raised bed, where you will have those raised beds, but they will be enclosed in a plastic tunnel. Which is good, because you create a more stable environment to control the drying and keep the rain off.

But a big issue in a lot of wet mills is that there is just not that much space in the wet mill. You know, a lot of wet mills are built on quite mountainous terrain. At the peak of harvest, when you're processing tons of coffee, you can very quickly run out of patio, and then you're going to have bags of coffee sitting around, possibly developing mould, getting off flavours, because you just don't have the space to process it.

One solution to this is mechanical dryers. Think of them like a very large tumble dryer. You generate hot air next door by burning something like wood, whatever's to hand. Air is pumped in and the beans circulate as the whole drum rotates very slowly.

Now, these mechanical dryers have had a bad reputation in specialty, because historically speaking they were used by very high volume producers who really just wanted to process their coffee as fast as possible, and the coffee they were producing generally wasn't very interesting. And this is a pattern, by the way, that repeats a lot in specialty: you taste an uninspiring coffee, you conclude that every way in which that coffee was made must be terrible, and then entire categories get written off — like mechanical drying.

Robusta is another example. The species of coffee, Robusta, has had a dreadful reputation for along time. It's most famously grown in Vietnam and ends up in cheap instant coffee blends. But we now have the emergence of fine Robusta, rebranded as Canephora, and its proponents are showing: look, you can grow delicious Canephora coffee if you treat it well.

The same argument applies here with mechanical dryers. The problem was never the mechanical dryer. The problem was how it was used, where coffee was blasted with as much heat as possible to dry it as fast as possible. If you use it gently and carefully, the cup quality can be great.

So, on to what good drying looks like today. Pressing play.

James: Okay Lucia, let's talk about drying. I would imagine a producer puts months of work into producing a great coffee. You know, they selected ripe cherries, they calibrated the pulper over and over again, they carefully managed their fermentation. The hard part is now over. And this final step is just about drying the coffee, getting the moisture down to about 10-12%. And really, how you get there doesn't matter that much. It's not as important as all the steps that came before it.

Lucia: Yeah, James, drying is a deceptively simple part of the process, because your job's done if you get the coffee seed down to, you Know, 10.5% to 12% moisture content. That seems simple enough. But it's an area that I care deeply about, because there's a lot of research that's really clear on what works and what doesn't in drying, and there's a huge gap between what the research knows and what I see happening on farms.

James: Okay, so what does the research say?

Lucia: Well, James, the research says that it does matter how we dry the coffee. Even if you do all of the previous steps perfectly, how you dry the coffee can undo that work. I personally follow and teach the recommendations set out by Flavio Borém. The recommendation is that we want to reduce the peak temperatures so that our coffee is not experiencing temperatures above 40 Celsius for a long period of time. And we also want to make sure that we're drying slowly enough that we're not damaging the seed.

James: Okay, so temperatures not exceeding 40 degrees Celsius. Can you spell out what the issue is if you dry too fast? And also if you dry too slow, which is also a problem.

Lucia: If you go too quickly, we know that that can compromise quality, but if you take too long, that also can compromise quality. So the challenges that I see producers facing are really high peak temperatures — that the coffee gets too hot, and that can damage the structure of the seed, so that we burst the seed and lose those contents, and the coffee gets kind of faded, it's like pre-aged.

And the other challenge is when we have these cooler, rainy periods, when it's unexpected, and the coffee is just taking too long, which means that the seed is in contact with high moisture for a longer time. With that moisture available, you're obviously susceptible to mould. And so your coffee is going to change and get defective in a different way. Both ends are a problem: if the coffee is drying too slowly, you have risk of mould, and if it's drying too quickly, you can lose those complex flavours.

James: Yeah, and they have to thread these two extremes at the same time. In Córdoba, Veracruz, Mexico, I spoke with Melissa de Gasperin.

Melissa de Gasperin: Welcome. Here's Rancho San Felipe. We're in Córdoba, Veracruz, Mexico.

James: Her family farm, Rancho San Felipe, is only three hectares, but attached to it is a large mill where she processes coffee, not just from her own farm but from neighbouring farms as well. And she told me about the challenges she'd had with drying.

Melissa de Gasperin: El detalle de Córdoba es que es muy húmedo. Nos pedían cafés especiales naturales, y los pones a secar y se te llenan de hongo muy rápido.

James: When trying to produce naturals, she'd put them out to dry and then discovered they were getting mouldy really fast. She also experienced problems the other way, where the midday sun in her part of Mexico is really fierce and would dry out her coffees too quickly.

Melissa de Gasperín: Que no le dé el sol de las 12 a las 2, para que no abra el pergamino y lo deshidrate muy rápido.

James: So she's confronting the issue of not drying fast enough and drying too quickly at the same time, at different times of the day. Lucia, let's now explore some easy solutions to fixing these problems.

Lucia: Okay, so regardless of whether you're drying on a patio or a raised bed, the priority should be to make sure that your coffee is not overheating above 40 Celsius. [unclear]

James: Right, but how do you take away the sun? You know, where coffee often grows, it's in tropical places where there's a lot of sun, a lot of heat.

Lucia: That's right, James. In the coffee belt, in the tropical areas, peak temperatures from the hottest part of the day, like 10am to 2pm, can be really high. So, for example, in Guatemala, where I live and process coffee, our UV index in the middle of the day can be 10 or 11. So, in order to protect the coffee and slow down the drying, I use a shade cloth that blocks out 60% of that sun. I think anybody can benefit from using one. And if you don't have such extreme conditions like I do, I would recommend a shade cloth that's a little bit lighter, something that blocks out maybe 40% of the light. Because lowering this temperature is not just good for coffee quality, it's also good for the humans who have to rake and bag the coffee.

James: Okay, what have you seen when a patio is covered from the intense midday sun?

Lucia: I noticed that when people are there working and helping rake and bag up the coffee, there's a little bit more attention paid, because it's a much more comfortable space to work in. Otherwise they want to bag the coffee as quickly as possible, because it's miserable.

James: Right — so it's about the comfort of the workers.

Lucia: The comfort of the workers.

James: Yeah. Right, use shade during the hottest times of day.

Lucia: And match your shade cloth to your conditions.

James: Got it. So Lucia, Melissa actually invested in drying tunnels.

Melissa de Gasperin: Y alrededor le vamos a cerrar con plastico también.

James: Right, so these are raised beds enclosed in plastic, with shade netting that she pulls across during the hottest part of the day. And she has fans inside to keep the air moving and stop the mould.

Melissa de Gasperín: Tener ventiladores — de hecho, llegaron ayer.

James: And controlling the environment like this should, in theory, make it easier, right, to keep temperatures down. So, should every producer follow Melissa's lead here and build raised beds and enclose them in a tunnel?

Lucia: Maybe. It depends. You know, if you already have raised beds, that's a great step, because raised beds get the coffee off of the ground, and so that allows better airflow, and because it's not in contact with the ground, it usually doesn't heat up as much. So raised beds can be a really great option.

But here's one thing that I've seen that can be a really big issue. You know, James, another name for raised beds is African beds. And I have worked in Kenya, I have worked in Rwanda, I have worked in Burundi. And something that I have seen is that those countries have a lot more labour than I have seen in Central America. I haven't heard as many producers complain that they don't have enough people. Because raised beds are a lot more work. When they're up off the ground, you can't mix them as easily and you need more people to move them. And so in Latin America, the more common way to dry coffee is on the ground, in a patio, because it requires fewer people to be able to move that coffee.

James: Yeah, right — because somebody with a wide rake walking, you know, you can turn over a lot of coffee that way on a patio, very fast. But folding coffee over itself by hand on a raised bed, that's just going to take a lot longer.

Lucia: So when the suggestion in Latin America is to get raised beds, the assumption is that you have five times more people to be able to move that coffee. So if you do, I think a raised bed is a great option. But if you don't, that doesn't mean that you won't get good coffee. You can also create really great coffee on a patio with the infrastructure that you already have. But what you are going to want to do is bring [unclear].

James: And so when it comes to controlling your drying, the great news is it doesn't require a lot of capital. Fans and shade nets are cheap solutions. However, for many producers, the issue is that they just can't dry fast enough. Drying can become a bottleneck, especially if the weather plays against you. So what could be a solution to that? Would you recommend a mechanical dryer?

Lucia: Ooh, I love a mechanical dryer, absolutely. I think a mechanical dryer is a great option in unpredictable weather patterns. And not only that, but it can also free up the bottleneck of patio space.

James: It's interesting though, because mechanical dryers in the specialty coffee world tend to have a bad reputation for quality.

Lucia: I think that's true. I think the reputation exists, but I think it's a false one. The mechanical dryer is a tool, and it's as good as the operator. So if we can use this tool a little bit differently, then mechanical dryers are completely compatible with really high-end specialty coffee. And one of those changes that we can make, like we keep talking about, is just lowering the temperature.

So I think the bad reputation of mechanical dryers came from the ability to kind of blast the coffee dry with high temperatures as quickly as possible to get producers out of a jam. But if we can just tweak their use a little bit, they can serve not just to get you out of a jam, but to consistently produce really high quality coffee.

James: Right. So, to get an idea of how to use a mechanical dryer, we spoke with Norberto Suárez.

Norberto Suárez: Mi nombre es Norberto Suárez. Estoy en Panamá.

James: He's a third-generation coffee producer in Boquete, where his family has been growing coffee since the 1880s. And at his scale, drying is an industrial operation.

Norberto Suárez: El complemento de las fincas — estamos hablando de más de mil quintales de cereza en el día.

James: His wet mill sometimes receives 45 tons of cherry per day at peak harvest. At that volume, patio drying is just not an option. There just isn't enough space. So he relies on Pinhalense mechanical dryers, because it gives him homogeneity and consistency across all his lots in how the coffees are dried.

Norberto Suarez: La calidad del café es mas homogénea, y la estandariza.

James: He runs his dryers at a maximum of 60 degrees Celsius, never pushing beyond that ceiling.

Norberto Suarez: En la secadora, 60 grados maximo y 40 minimo.

James: Coffees go in at around 30% moisture and then come out in that ideal range 24 to 30 hours later. And here's one technique worth noting.

Norberto Suarez: Ahora lo metemos en las secadoras con aire frio por 12 horas.

James: Usually he dries his coffee on the patios first, before putting it in the dryer. But sometimes there's no space. And so when coffee comes straight off the depulper, he runs it through the dryers on cold air first, for 12 hours, before then switching on the heat. This removes the surface water gently.

Lucia, what do you make of Norberto's protocol here? You mentioned earlier that coffee should never get above 40 degrees during drying, but the air in his mechanical dryers is 60 Celsius.

Lucia: Yes, this is a great clarification to make. What matters is that the coffee seeds themselves don't rise above 40 degrees. And that for honeys specifically, they don't go above 36 degrees — honeys have a lower threshold.

So, with large dryers, because of the sheer amount of coffee inside, it's possible that Norberto's coffee stays within the desirable range, even if the air temperature is higher.

James: Right, okay. So the air can be 60 degrees, but that doesn't mean the beans are going to be 60 degrees — they're probably going to be lower.

Lucia: That's right. [unclear]

James: All right, a final question. What's better: dry first on the patio and then finish in the dryer, or the other way around?

Lucia: That's a great question. What I've seen is that if producers do have a mechanical dryer, they tend to dry the coffee in the traditional way, whether it's patios or raised beds, first, and get it kind of dry to a certain point. And then they'll finish the coffee off in the mechanical dryer. Because the water in the beginning, it's much more free and more available — getting the coffee from 50% moisture content down to 20 is pretty easy. But once you get past the 20%, that water is bound more tightly. It doesn't want to dry. It can be really frustrating to finish that last bit. It just takes so much longer to finish that 20% down to 11 than it did all of that other water.

SoIsee a lot of producers use the mechanical dryer at the end to finish the coffee. And at this point, this is when the coffee is the most brittle, it's the most delicate, and then you're hitting it with a big burst of energy. And this tends to destroy the structure of the seed, kind of releasing those volatiles, releasing the contents and making the coffee more susceptible to fade over time.

So my recommendation for producers is: you can still use your mechanical dryer to help you manage your patio space, but it's something that I would recommend using first. Use it at the beginning of your drying process, when you have the most water. And then let that last bit happen more gently — use your patio space when the coffee is already at 16% moisture content, and dry it slowly so that you avoid the damage.

James: Now Lucia, I just want to point out to the listeners that what you're recommending here — drying first in the dryer, then putting it on the patio — that actually goes against the advice of Pinhalense. So, just to be clear, what you're advising here is a bit unconventional.

Lucia: [unclear] I have found that switching that order allows you to keep the coffee in storage longer. That way you've increased the shelf life of your coffee, and then you can find new buyers. So, again, this is really only when you're looking to find a different market.

James: Okay, so now let's sum it up.

Lucia: You want slow, steady, controlled drying. That consistency is what's going to standardise your coffees from lot to lot. Standardised coffee is what buyers are looking for. It builds long-term relationships and ultimately is what translates to better prices and more profitable farms.

And the great news is that these investments are modest, like a shade cloth to reduce peak temperatures, or a fan to keep air moving and reduce mould growth. And if you have the capital, I recommend a mechanical dryer. A mechanical dryer is not just helpfulina weather emergency — I believe that they can be part of a regular protocol for making quality coffee.

James: And now, coming up next: the instruments, data and systems you need to make your post-harvest processing carefully controlled and reproducible.

James: Pressing pause. To keep these episode lengths manageable, we are going to take a break. Coming up in the next episode, we conclude here on post-harvest, looking at the instruments producers can use to better control their post-harvest processing, and the big issue with water waste, which no one wants to talk about, but which is a massive issue on many farms. So I'll see you in the next episode.