New Supplier, New Coffees, and More Data

Over the past few months I have changed my coffee buying habits in a lot of ways. For a while I had been buying things in bulk (5 pounds or more). The end result is that I ended up with a LOT of coffee. It is more cost efficient to deal with some of the green coffee buying clubs compared to retailers, but I had been finding the coffee more hit or miss than I would like. In the end, I decided what I really like is VARIETY and really high quality coffee. I would rather have 10 one-pound lots of really individual and fantastic coffee than 10 pounds of a mediocre coffee, even if it costs me significantly more. Net net: I switched to buying most of my coffee from Sweet Marias, much as I had done when I started out in this hobby years ago.

Anyway, fast forward to a few weeks ago, and I came across a posting from the Green Coffee Buying Club about a discount that was being offered from Roastmasters.com. Happy alarm bells started ringing in my head for a reason that took me a day or two to work out. Turns out that Roastmasters is the green coffee/home roasting endeavor of one of my favorite coffee shops - Willoughbys.

You see, my infatuation with great coffee started at Willoughbys in New Haven, Connecticut during my years as a grad student. I had drunk coffee all my life, but finding Willoughbys was like finding an oasis in the desert. They roasted all their own coffee, had tremendous variety, and the brewed coffee they offered was like being in a different galaxy compared to what I had been drinking. In short, I was hooked, and stopping by the cafe became part of my daily ritual. Some of my nicest memories are of me and my wife hanging out outside the cafe, drinking coffee together, enjoying the sunshine, and having a bagel at breakfast time. Even after I graduated and moved to New York, mail-ordered coffee from Willoughbys was my modus operandi.

Realizing this, it wasn't hard to convince myself to buy some green coffee from them. What is really nice, though I haven't done it myself, is that you can buy the same exact coffee from them roasted, as well as the green beans, to try your roasting chops against them. This is a really nice option for those who are learning to roast.

So far I have tried a few coffees from their selection, and they have been really good. They are a bit on the pricey side, but the shipping from Connecticut is a whole lot faster then buying from Sweet Marias. I will definitely be a repeat customer.

The first coffee I tried was an Ethiopia dry processed coffee, Amaro Gayo. These beans have made the rounds lately, gaining a name for themselves as a really nice cup. I have to agree- a City roast I did was packed full of berry aromas and tastes, with a solid cocoa background. I'm glad I bought a couple of pounds. The next coffee I roasted was a lovely, light Guatemala Antigua by the name of "Finca Columbia". As usual, I was playing around with roast profiles, and I managed to come up with a temperature progression I really liked. Here is the derivative curve, as I discussed in my last post. I should also fess up that I did a rolling average to clean up some of the noise in the data.



The roast profile for this coffee was 80% power to start, dropping to 70% at 360 degrees. I have been looking at these derivative curves for a while, and something jumped out at me suddenly. There is a common trait in this temperature data - the rate of temperature change drops consistently at first crack. Thinking a little more, this makes perfect sense; at first crack the water in the beans is powerfully boiling off (hence the cracking sounds). The heat being applied to the beans at this point is going into this reaction, instead of driving the temperature of the beans up. Similarly, at about 400 degrees or so (about 13.5 minutes in this graph) you see an uptick again. This is the point at which you have a City roast - first crack is ending, and the beans start to expand more before eventually reaching second crack. I have overlaid a lot of roast data, and these characteristics are very consistent. It points toward some interesting ideas in terms of roast control, and I see that other folks have also picked up on this in cyberspace, designing controllers and real-time data collection devices to track this rate of temperature rise.

Here is another example I added to the same chart:

This is a Kenya I roasted, and you can see how these derivative charts are useful. I started using the same exact profile as the Guatemala in the previous example, and noticed that it was taking heat slower than I expected. In retrospect, it isn't surprising since Kenyas are such high-grown, dense seeds. I won't bore you with any specific heat calculations, so never fear....

Anyway, you can see where I increased the heat flow and the subsequent rise of the curve, and again the drop when first crack arrived. These diagnostics are very interesting indeed, and I have some other ideas to make them better. By the way, that Kenya Muranga'a was super-intense, sweet, and fruity. Great stuff.

Engineers Gone Wild

One of the things that has been troubling me for a while is better understanding the differences between roast profiles. A change in how a coffee has been roasted, even when the final temperature is the same, can be dramatic. However, looking at the temperature data doesn't always tell the story. Here is a good example:


This is two Kenya beans that were roasted differently. The differences in the curves are quite subtle even though what I was changing in terms of temperatures, times, and fan speeds were very different. Even roasts that were absolutely terrible, like the experiments I did on high drop temperatures, show barely a difference in the roast curves. Some of this is due to the fact that the scales are large since you cover a sizable temperature range in the roast, but some of it is just subtlety in the temperature profile producing large effects in the taste of the coffee.

I was playing around in Excel the other day trying to determine if I was just fooling myself that I have any control over the roasting process. I decided that I needed to look at the data another way, so I decided to take the derivative of the temperature data and see if anything illuminating happened.

Without getting into the mathematical details, the 1st derivative is essentially the rate of change of temperature as a function of time. Taking the same two coffees, plus a third example, you can see the data this way:


The x-axis is still time, but now the y-axis is the change in temperature per unit of time. You can see when the coffee is dropped in at time=zero, there is a huge temperature drop (this is why it is a negative number), and eventually it recovers to something between 10 and 50 degrees of temperature increase per minute until the end of the roast.

One interesting fact immediately popped out after looking at a few charts like this. On the experiments I did with a higher drop temperature, the rate of temperature decrease when the beans are added is substantially higher than when the coffee is dropped at a lower temperature. I am not sure why this is (or if it matters), but I could imagine that that heating element is still on and going strong for the lower drop temperature, and in the other case the environmental temperature and thermal mass have stabilized such that the heater is not on as much. Anyhoo....

The more interesting data is when you zoom in around the region from first crack to the end of the roast:


Don't worry too much about the noisiness in the data; that is typical of this sort of data analysis and the sample size I have used. A couple of things are interesting here. First, I strive to keep a roughly 10 degree per minute temperature rise from first crack to end of roast. You can see that these roasts are doing pretty well. Looking at the earlier times, you can see my attempts to ramp down the heat as first crack approaches in order to have a nice slow, steady progression through that phase of the roast.

The dots on the graph indicate where first crack began on each roast. You can see that the roast of the Kenya Tambaya had a slower ramp rate at first crack than the other two. This is exactly what was intended. I am trying to develop a roast profile that very gently enters first crack. By looking at these curves, it is evident that it is working. The other two Kenya roasts were roasted with the same profile, hotter going into first crack, and the data shows this clearly.

I'll be looking at these derivative curves more as time goes on. It really hones in on important parts of the roast. Amusingly, I came across some other posts on the web where people are actually building micro-controllers for their roasters that track this same 1st derivative data as a hands-on tool for roaster control. Mediocre minds think alike and all that.

Mathematics aside, you are probably wondering how the coffee tastes with the slow entry into first crack. The initial data is extremely promising - very sweet coffees with well integrated acidity and no grassiness. Stay tuned for more coffee reviews.

Drop Temperature and Ethiopia Birbissa again

If you have paid any attention to the roast profiles I have been posting with the Hottop, you'll see that the coffee is typically getting to about 300 degrees in 5-6 minutes. This drying phase is important, as I have talked about before, and really sets the stage for what the coffee is going to taste like.

There are some hints out there that drying the coffee a bit faster can have positive qualities in the cup (more sweetness/acidity, less woodiness), so I started thinking about how to do this.

Unfortunately, all electrically powered roasters are very underpowered. You really need a gas-fired tool to have a significant effect on the ramp speed. Since a gas powered roaster isn't in the cards for me any time soon, I decided to play around with the temperature at which the coffee is added to the roaster. Letting the roaster pre-heat more, I surmised, would speed things up. It did indeed, but with less than stellar results, I am afraid.

Here is a graph of Ethiopia Birbissa with the two roasts:

You'll see that the roast that had the coffee added at 400 degrees did recover faster, and the earlier part of the roast was overall somewhat shorter. The total roast time and final temperature were the same. Comparing my notes from the original roast to this new one was like reading about two different coffees. While the first one was a fruit bomb, the higher drop temperature roast was woody, flatter, and much less interesting. I am not sure if there was a bit of scorching going on or something else, but it wasn't a positive improvement. I did a second test with some Red Sea Blend at the higher drop temperature and had a similar result. Rather than increasing sweetness and/or acidity, these coffees were flat, uninteresting, and overly woody.

It looks like it is back to the drawing board a bit. I have had some really excellent coffees lately with a more traditional roast profile which I hope to post about soon. Also, I may play around with smaller roast loads to see if the ramp speeds can be modified in that way instead of with the drop temperature.

Columbia "Dos Payasos de Tolima"

Well, the few readers of this blog won't be surprised that life intruded once again on poor Scotto, making blogging very infrequent. Rest assured that roasting and drinking coffee has not gone by the wayside; in fact, it has gotten even more interesting. More on that later.

I have been in stash-reduction mode for green coffee for quite a long time. Recently, I finally got around to ordering some more coffee from Sweet Maria's after a long hiatus. Boy, did I forget how stellar the beans are. I buy a fair amount of beans from places like the Green Coffee Buying Club and such, largely because it is inexpensive. It is possible to get good, and occasionally, very good coffees from there, but the coffee from Sweet Marias is uniformly suberb. It is a bit more expensive, but you are essentially paying Tom to be your personal taster and quality-control guy.

This Columbia is a revelation for a fatigued palate. I roasted it inside (Yay! No more freezing garage with the Hottop - more on that another time) and produced a roast curve as follows:

You can see the power levels (the fan was set at 25% for the entire roast) and the boxed area where 1st crack was.

Roasting inside is taking some adjusting in profiles, as the behavior is different from the cold garage. Things were a bit quick at the end, but the coffee was still excellent. It is sweet, sweet grapes all the way in this one. There is a perfect, sparkling acidity, raisins, and an unctuous quality to the coffee that lingers forever. If you like Kenyas and such, you should definitely check this one out. It is an intense coffee, and one of the best Columbias I have had in a while, perhaps since the Cerulean Warbler.