Dear patient reader,
Some unexpected effects on barista techniques, specifically on monitoring the flow rate, have come up after we dropped robusta from our blend a couple of months ago.
Background: After sourcing mild flavorful robusta coffee in the mid ’90’s I have used robusta in our blends to enhance crema viscosity, mouth-feel, and duration in the cup. Then in 2001 we finally cracked the temperature problem on the espresso machine by introducing PID control of the coffee boiler and adding a pre-heating tank for the brewing water on a two-group LaMarzocco Linea. (For details find “Italy Meets Omega” in my archives at www.espressovivace.com/archives).
When the temperature of the brewing water is held constant at 203 degreesF. (at sea level) we were able to preserve the natural sugars present in our roast through the brewing cycle into the cup. Our espresso became much sweeter. I immeadiately noticed that the crema became very fragile and the duration became 30 seconds instead of lasting for over one minute in the cup. (The mouth feel became even more heavenly though, with a downy lightness impossible to express with words.) I called up Carl Staub the food scientist specializing in coffee and asked him “what’s up with the fragile crema Carl?” He asked right away “Is the coffee sweeter David?” I said it was much sweeter. Carl said that the increased sugar content would have a negative effect on crema life in the cup….something about the sugars breaking the long-chain surfactant molecules responsible for stable foam.
So finally in early 2009 I have concluded that crema longevity of sweet Northern Italian espresso is not helped by the addition of robusta in the blend. We have had an all arabica blend for about two months.
What I did not expect was the effect on flow rate management by the barista. Previously my pour would slow down towards the end of the shot noticeably. This quality is attributed to the use of conical grinders at Vivace that produce micro-particles that add much to the flavor and texture of our espresso. But, they migrate down in the packed cake of coffee during brewing and make a fine mat in the bottom of the coffee basket, slowing down the flow rate. This made my baristi struggle a bit to hit the mark of 23 seconds for 1 and 3/4 oz dpouble shot as they had to guess where it would end up as it slowed to a stop just at the finish line in the cup.
So why has it changed? The robusta we were using is Monsooned Indian Robusta. One of the characteristics of monsooning coffee (paradoxically) is that the finished roasted coffee has a much lower internal moisture content, thus requiring a finer grind than the other beans in the blend. A finer grind produces a signifigantly higher percentage of micro-particles than a slightly more coarse grind. (As a matter of fact, brewing pure monsooned robusta, the pour starts out fast and chokes to a complete stop at about the one ounce mark).
So the net moisture content of the blend was made a bit lower with the robusta in it. (Robusta was used at 14% of the blend). This created a finer overall grind for the blend, the effect was a slight increase in micro-particles in the blend creating the problem of the slowing flow rate of the coffee. With this coffee not present in the blend the total moisture contect increased a bit, leading to a slightly more coarse grind and less particle migration during the brewing cycle. Now we have more control over flow rate and shot cut-off, one of the truly dominant factorsa in a perfect cup.
After twenty-one years you can see why I am not bored with my beloved tricky coffee. It always throws us a curve ball.