ROASTBUSTERS

OFTEN IN THE SPECIALTY COFFEE INDUSTRY, we hear “rules” from other professionals. Sometimes the rules make sense (e.g., cleaning out your ducting and chaff collector frequently to help prevent fires), but there are also times when people offer advice but have little to no evidence to back up what they’re saying.
     To me, it’s like that great old story about cooking holiday ham. If you haven’t heard it, it goes like this: In this particular family, the mother makes a holiday ham every year. And every year, she cuts three inches off one of the ends. Why? Because that’s the way her mother taught her. If you ask her mother why, she’ll give the same answer, “Because that’s the way my momma did it.” You have to go back another generation before you finally come up with the root of the tradition. Turns out, great-grandma cut off three inches of ham because otherwise the ham was too big to fit into her baking pans.
     So for the next two generations, ham was being wasted, all because no one understood the “why” of cutting off those three extra inches.
     Likewise with coffee roasting (or any passed-down craft, really), we’re given lots of information from elder roasters, roasting colleagues, and that bastion of knowledge and misinformation, the Internet. Some of it is truth, some of it is tradition and much of it has gone untested. And that’s where the fun comes in. If you’ve ever been sitting around thinking about coffee and wondered, “Why in the world do I do this?” this column is for you. Each issue will take on a new question and the truth will be put to the test.

EPISODE 1

Robusta & Crema: A Good Relationship Gone Bad?

One topic that comes up again and again, especially for roasters who are supplying competing baristas with espresso, is robusta and its role in espresso blends. The prevailing belief is that robusta is a necessary addition to espresso blends because of the way it increases crema volume and persistence.
     I decided to take a further look at this and explore it in some depth. To begin, I wanted to see what some of my roasting brethren were offering up in the way of robusta-containing blends, so I went to some friends at the Roasters Guild and asked for some samples of their espresso blends. Once I had all of the samples, it was time to start pulling the shots.

Experiment #1

I started with six espresso blends, all of which contained a percentage of robusta. In an effort to limit variables and make sure that the espressos were being evaluated consistently, I pulled three double shots of each blend, using a La Marzocco Swift grinder for each to help ensure a relatively consistent dose and tamp.
     The shots were pulled using a La Marzocco FB80 3 EE set at 9 bars and at 201 degrees F. Shots were pulled between 25 and 27 seconds into two 50 ml beakers, filling each beaker to approximately 30 ml.
     The volume of crema was recorded (accurate to 5 ml) and the persistence of crema was timed. (The end point for the crema’s persistence was when the black espresso was clearly visible through a hole in the crema.)
     Taking a look at this small amount of data, we see that there isn’t really a linear relationship between the amount of robusta in these blends and the amount of crema they produce or how long the crema lasts. But what if the various other components of the blends are contributing to or negating the effect of the robusta? More data was needed, and so it was time to get back to the roasters and make up some espresso blends!

Experiment #2

Since the range in the percentage of robusta in the blends varied, as did the other ingredients, I had to make up some blends of my own. In an attempt to keep the experiment simple, I opted to use only two coffees in my tests. The robusta component was a washed Indian Mysore that I purchased from Sweet Maria’s. Following their recommendation, the coffee was roasted into second crack. The robusta was paired with a coffee from the Norte region of Peru. The blends were allowed to rest for five days before being pulled in the same manner as the previous shots.
     Looking at this data, we see that while there isn’t necessarily a significant increase in the volume of the crema produced, we do see an increase in the crema persistence in the blends that contained 15 and 25 percent of the robusta. Interestingly enough, the shots with higher concentrations of robusta seem to show a decrease in the blend’s ability to retain crema.

So what does it all mean?

In the end, the results show that while there does seem to be a relationship between the persistence of the crema and the percentage of robusta, there was not as much evidence to support the theory that robusta helps increase the volume of crema. While it seems a bit strange to see the persistence of the crema negatively affected after a certain ratio of robusta to arabica is breached, a bit of research turns up a similar study done in 1989 by Marino Petracco for the International Association of Coffee Science’s annual symposium on robusta espresso and arabica espresso. That study showed that when “cup testing” robusta espresso and arabica espresso, robusta tended to display a heavier mouthfeel than arabica at first, but that if the prepared espresso beverage was held in the mouth longer, the body of arabica espressos lingered while robustas would fade. Petracco put forth that this was possibly due to a higher rate of gas release from robusta coffee. Since crema is a foam made up of gas bubbles trapped in the liquid, it’s not too far of a stretch to say that this could also be an explanation for the results that we saw in our experiments.
     One other important thing to note in regards to this experiment: taste, or rather the lack of it (and I’m not referring to myself here). While I tasted all of the espressos provided to me, as well as the experimental ones, this experiment was focused strictly on the physical aspects of the crema. This was done in an effort to simply present data that roasters could use to formulate their espresso offerings. Espresso blending is a true stylistic choice of a coffee roaster, and while the physical appearance of the beverage is important, it’s also important that we do not de-emphasize the taste. After all, with espressos, while the consumption of the beverage is typically quick, the taste is what lingers.

Gee Barger is a roaster for Counter Culture Coffee in Durham, NC. In his spare time he writes two blogs, hosts a weekly trivia competition, and enjoys drinking beer. He’d love to hear about other coffee truisms you’d like to see tested, so drop him a line at gee@counterculturecoffee.com.