9 Bars
Espresso Quality: Brewing with the new PID Machines
by David Schomer, Espresso Vivace


Espresso Quality PID machines are the new generation of espresso machines using PID process controllers to stabilize brewing water temperature during brewing. To the best of my knowledge, Treuh (now called Synesso), La Marzocco, Conti of Monte-Carlo and John Bicht of Versalab have produced espresso machines using its technology.
   PID means proportional, integral and derivative programs combined into one small processor to control a function, such as keeping a boiler very near the set temperature. Proportional means that the closer you get to the set point, the controller will turn on the heating element for shorter and shorter intervals of time. Integral and derivative refer to sophisticated programs to dampen oscillations, making sure you do not get into a pattern of over-shooting and then dropping below the set point.
   When I began temperature studies in the early 1990s, the best machines featured water temperatures that wandered around about six degrees Fahrenheit when measured on the coffee bed. In espresso machine design, the group head and the water heating system combine to produce the final accuracy of the brewing water temperature. I had come up with a modification to the group head of a La Marzocco that reduced the range of error from six degrees to about two degrees, essentially making the coffee bed temperature performance as good as the boiler control with a two-degree mechanical thermostat. The coffee became thicker and sweeter with a deep red-brown color on every shot. But I still could taste some astringent/sour shots among some very sweet ones. Clearly, a two-degree range was not good enough to capture all the sweetness in each shot we brewed. Then, on Ash Wednesday in 2001, I applied a PID controller to the boiler with help from Roger Whitman at ESI in Seattle and John Bicht of Versalab. Perfection became possible. This early work has been credited by La Marzocco and Synesso as being the inspiration for the new generation of espresso machines.
   What can we expect from the espresso when brewing water temperature is held stable?
   Well, first, the good news. It is finally possible to capture the fragrance of the fresh-ground coffee beans in a liquid to be enjoyed as a flavor/aroma experience. Simply put: The coffee can taste as good as it smells. Preparing my own Dolce blend years ago on a prototype La Marzocco that held the temperature error to within 3/10 of a degree Fahrenheit, the sweet flavor brought tears to my eyes. The espresso also featured monster crema. So much of it that it overwhelmed the delivery spouts on my portafilter and oozed out of the hole in the middle.
   The crema featured a mouth-feel I had never encountered. A quality of butter melting over the tongue that is the hallmark of this new espresso. The crema has an incredibly light, chiffon texture, offering untold delights when enjoyed at the bar, but it has a shorter life-span than crema I have produced on this blend in the past. After much testing (we have brewed on these machines at Vivace since 2001) I concluded that my crema collapsing more quickly was a fact with these machines. I inquired with several food scientists about this phenomenon. They asked me if the coffee was sweeter. “Is it sweeter?” I exclaimed, ready to launch into a frenzied description of the blessings raining down upon my senses from this coffee-heavenly body, caramelized sugars, notes of chocolate, butterscotch, anise earthy tones from the Harrar all balanced against a toast-crust flavor from the roast—orgasmic! But, it was a long distance call, so I said, “Yes, very sweet.” Well, the consensus is that the sugar structures are acting to shorten the life of the foam. And, I believe it.
   More than ever, café espresso must be enjoyed at the bar in pre-heated porcelain cups. And for those who want to add sugar to the espresso, we have developed a recipe to liquefy sugar in the cup and draw the espresso onto that; swirl and serve. Otherwise, the sweet, delicate, impossibly fragile espresso would never survive long enough for the sugar-adder to add sugar, heaven forfend.
   Many people had trepidation about this technology, fearing that these machines would make the coffee for you and remove the art from the hand of the barista. Of course, quite the opposite is true. With perfection possible, mistakes are very apparent and disastrous in their consequences. When you are flying really high, you have farther to fall. It is as if all this precision focuses just as easily on undesirable compounds, concentrating them as equally as the caramelized sugars can be concentrated. When temperature is a little low, say 201 degrees Fahrenheit, you have a concentrated sourness in the espresso. Previously it might just be a little sour.
   Flow rate of the espresso shot has become far more critical with these machines. Classic technique is that the espresso should hang like the tail of a mouse and take from 25 to 30 seconds to brew the shot. And you cut the shot off when the color begins to lighten. In the past, when the pour was a little fast or slow, the espresso’s flavors were changed a little bit. A little fast meant a little bland, and slow pours were a little bit burned-tasting. With the temperature stabilized machines we notice even slightly fast pours are markedly sour with slow pours acting about the same as before. (Faster flow has the same effect as low brewing water temperature on the espresso.) To get the very sweet espresso, flow-rate must be perfect, a hanging pour with an open flow, not dripping through middle of the cycle, and perhaps an elapsed time closer to 20 seconds, counting preinfusion, for the shot to pour. Flow-rate has become a knife edge the barista must walk to create this beautiful coffee experience.
   If the machines are not cleaned properly, accumulated oils are far more detectable in the espresso flavor on these machines. These machines highlight the inadequacy of brass brewing surfaces. We have known for years that brass, being porous, was difficult to keep clean as coffee oils would get lodged within the porous surface of the metal and add a rancid flavor to the espresso. The new designs by Treuh (Synesso), and La Marzocco have replaced the brass diffusion blocks in the group-heads with stainless steel. This is essential with this new technology.
   PID machines have also highlighted the group head designs, and particularly the thermal behavior of the diffusion-block residing just behind the dispersion screen. It is one thing to stabilize the brewing water boiler (heat-exchange machines are always very unstable in regard to temperature, with or without PID controllers), but quite another to bring all that wonderful stability to the coffee in the porta-filter. From the barista point of view, preheating the group head just prior to brewing the shot has emerged as one of the critical techniques to producing truly sweet espresso. In my video I called this technique ‘temperature surfing,’ running about two ounces of water through the group just before brewing the shot. It is interesting to me that this technique remains so useful on all technologies I have tested. The old heat-exchange machines may accumulate heat as brewing water rests in the heat exchanger itself. They will cool off a bit when you run a little water through. The old dedicated boiler machines (Conti and La Marzocco primarily) heat up a bit in their connecting tubing and on the diffusion block surface.
   The new La Marzocco and Treuh (Synesso) designs employ stainless steel diffusion blocks, which cool off a lot more slowly than their brass counterparts while the barista packs a shot. Brass is still commonly used on most espresso machines. Clearly, if your brewing water is heating up the diffusion block during the brew cycle, your temperature is going to start lower than your target temperature and rise during the cycle of the shot. Pre-heating or ‘temperature surfing’ is essential to avoid this.
   Controlling brewing water temperature truly elevates café espresso to a culinary art. The skill of the barista is highlighted by this technology with subtle nuances of technique being revealed as having a big impact on flavor. Espresso blending can now be advanced, as roasters can taste varietal nuance with all the precision of the cupping method. And, of course, machine materials and designs can be refined as improvements in the flavor can be relied upon to originate with the design change in the machine, rather than being the result of temperature wandering around like a drunken sailor. These machines mark the culmination of humanity’s five-century quest to seduce the fragrance of fresh roasted coffee into a cup.

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David Schomer is an espresso roasting and preparation specialist and the owner of Seattle, Wash.’s Espresso Vivace. He can be reached through his Web site, www.espressovivace.com.