Barista Magazine

APR-MAY 2019

Serving People Serving Coffee Since 2005

Issue link:

Contents of this Issue


Page 31 of 119

F O A M : N E W S + T R E N D S GETTING UP CLOSE AND PERSONAL WITH TEMPERATURE PROFILING VIA THE RANCILIO SPECIALTY RS1 Maybe the best—as well as the most vexing— thing about coffee is that the more you learn about it, the more complex it becomes. That's why the engineers at Rancilio asked themselves while designing their latest espresso machine, why add more complexity with an espresso machine? Therefore, their goal with the Rancilio Specialty RS1 was to make espresso more consistent while making the process easier. They achieved that by integrating two main technical features: tempera- ture profi ling and variable steam. Temperature profi ling gives the barista the option of adjusting the beginning and end brewing temperature for espres- so, while variable steam provides the operator with the ability to control steam delivery via the software on the four steam lever power levels. So what does all this technology look like behind the bar, and how does it add consistency? WHAT IS TEMPERATURE PROFILING? Temperature profi ling is the act of controlling the amount of heat admin- istered throughout a process. This is done when coffee is roasted and is how coffee experiences temperature in every brewing method. (Similar to roasting coffee, we'll examine extraction mainly based on the coffee temperature rather than only focusing on the input, heat temperature.) When brewing a pourover, the water temperature in a kettle drops over time, causing the extraction temperature of the coffee slurry to peak and drop. Even when brewing espresso on a fl at or unchanging profi le, the espresso puck experiences a gradient and brews 30 percent or more of its extraction time below set-point temperature. In the RS1, the beginning and end temperature values are set by the barista. A system of hydraulics controlled by a computer determines how much to heat or cool the system to achieve the desired temperature profi le. First, hot water is brought from a heat exchanger into a microbo- iler where a heating element maintains temperature with a temperature probe. At the same time, ambient water is brought into the microboiler. The purpose is to introduce fresh, oxygen-rich water into the group with every shot. To temperature profi le, a valve sending ambient water straight into the group operates on an algorithm, pulsing water to achieve the desired profi le. The system uses the impulse readings from the fl owmeter to understand how much to cool or heat the incoming water to the group in order to achieve the set profi le over the course of the shot. Temperature is adjusted per group in the touchscreen display, where variable steam pressure delivery across the four settings can also be adjusted. The steam delivery is controlled by the machine's levers, which have two power set- tings to optimize steam delivery for different drink sizes and milk types. WHY USE IT? To understand why adding a variable can make espresso more consistent, it's helpful to unpack what's happening during extraction. A roasted cof- fee bean is incredibly complex, with upward of 1,000 chemical compounds. During a coffee extraction (assuming everything else is constant before extraction, such as grind particle size and uniformity, water quality, etc.), there are three main variables determining solubles yield and affecting which taste-attributing compounds are extracted: coffee and water contact time, extraction temperature, and turbulence of the water in the coffee slurry. Of these three, temperature is the most infl uential. It dictates what compounds are dissolved in liquid and at what rate. When dealing with the demanding intricacies of coffee, being able to hone the temperature profi le that coffee receives, like during roasting or with a pourover, opens up the possibilities to more fl avor profi les. Let's dig into the science here for a moment. The extraction of taste-attributing compounds in coffee is best described as a process of varying extractions of chemical compounds. This is opposed to a simple idea of more or less "coffee taste" or a simple calculation of solubles yield. These chemicals are generally extracted in the following order: Salts and some acids are dissolved fi rst. Next, sugar-like compounds and carbohydrates are dissolved. After that, compounds contributing to bitterness and body are dis- solved, such as chlorogenic acid, trigonelline, and complex carbs. Next, with increased temperature and agitation, compounds that are not usually water soluble break down, including solid suspensions, gases, and liquids. Then, oils and waxes combine and enter the solution. Finally, with high enough temperature, the cellulose (bean fi ber) breaks down. All of these compounds are being broken down to some degree during the extraction process, with varying amounts of evenness and consistency depending upon the temperature and fl ow dynamics of the extraction. While compounds follow a general rule of extracting more at higher temperatures, the increase is not always linear, and the rate of extraction varies from one compound to the next. For instance, chlorogenic acid extracts at a disproportionally different rate at a lower temperature than it does at a higher one. Certain elements are extracted immediately, even at room temperature, and some elements will only extract readily at high temperatures. This principle of coffee brewing is partly why extraction is so complicated, and why varying brewing styles can yield vastly different results with the same coffee. Simply put, temperature profi ling with espresso is a different brewing method that provides a precise tool for highlighting specifi c taste charac- teristics of the coffee. Given its extreme complexity, the more consistent and exact the brewing process, the more likely the espresso that is served to customers resembles the way it was dialed in. GROUP TEMPERATURE DELIVERY VS. ESPRESSO EXTRACTION TEMPERATURE 32 barista magazine

Articles in this issue

view archives of Barista Magazine - APR-MAY 2019