Barista Magazine

DEC 2017-JAN 2018

Serving People Serving Coffee Since 2005

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Page 27 of 107

28 barista magazine F O A M : N E W S + T R E N D S THE SCIENCE OF BALANCE So, apart from taming the temperature gradient, how can temperature profi ling affect the taste of espresso? The short answer is that it varies across different coffees and it fl uctuates across different coffees. Coffee is incredibly complex, so much so that many studies confl ict on what exactly affects the taste. Espresso is composed of hundreds of chemical compounds, and the water that constitutes 90 percent of its makeup is prone to vast regional and daily variance. However, thanks to a recent study, we can see how select temperature profi les can change espresso's chemical composition on a molecular level. The study "Extraction of Espresso Coffee by Using Gradient of Temperature" was published in the scientifi c journal Food Chemistry in early 2017. The goal of the study was to examine the physicochemical and sensory characteristics of temperature profi ling with espresso. For each coffee tested in the study, a ramp-up temperature profi le was used (88–92°C +/- 0.35°C), a fl at profi le was used (90 +/–0.35°C), and a ramp-down temperature profi le was used (92-88 +/- 0.35°C). Although the average temperature for each profi le was similar (90-90.5 +/– 0.35°C), the chemical compounds pulled into the cup varied greatly. While several measurements were taken at each profi le, we will focus on one group: total polyphenolic compounds. Though much is still unclear about the specifi c contribution of polyphenols to fl avor in coffee, they are generally known to lend bitterness and acidity to the cup. Among its constituents, the acid group known as chlorogenic acids (CGA) is likely most infl uential on taste. CGAs are more present in green coffee; between 40–95 percent are broken down (loss increases with roast degree) into quinic acid, caffeic acid, and other phenolic by-products, such as lactones and melanoidins, during roasting. For a washed Arabica espresso, using a ramp-up temperature profi le increased the total polyphenolic compounds extracted by 47 percent compared with a fl at temperature profi le. Alternatively, a ramp- down temperature profi le reduced polyphenols by 24 percent compared with a fl at temperature profi le. Specifi cally, the ramp-down profi le showed an 8–per- cent decrease in chlorogenic acid compared with the fl at profi le, and a 20–percent decrease compared with the ramp-up profi le. It is also interesting to note that the ramp-down profi le showed a 30–percent increase in lipids (a group of chemical compounds that contains oils and fatty acids) compared with both the fl at and ramp-up profi le. The dramatic effect on polyphenols is just one instance that demonstrates the effect of profi ling temperature on the rate of extraction for a group of chemical compounds. While this information is huge from a scientifi c perspective, it can seem intangible to the practical application of a specifi c temperature profi le to a particular coffee in a coffee shop. While baristas and the scientifi c community may not have fully connected the dots between utilizing variables to coax out specifi c fl avor profi les and the exact science behind why or how the espresso becomes balanced, we can look at what the coffee experiences to inform a practical application. By looking at the test conducted above, we can see that a slightly declining temperature profi le can heat the espresso-brew- ing environment quicker. This information is helpful when analyzing the fl avor profi le and determining which variable adjustments provide the most pleasing cup. More tests like this one across a range of profi les and machines are necessary to inform baristas about what exactly their espresso is experiencing. Even when not profi ling temperature, this conversation will aid in reframing the idea of temperature from a static boiler setting to a dynamic gradient that the coffee experiences that can be infl uenced, with the ultimate goal of more consistent, better-tasting espresso. So what are the practical applications of using temperature profi ling? Experientially, I've found that a ramp-up profi le increases complexity The Temperature Profi ling technology was pioneered by Rancilio in 2008, and works by utilizing a microboiler that is built into the top of the grouphead. This system introduces cold water into the microboiler with every shot, providing a small but signifi cant fl avor increase. The boiler regulates its temperature utilizing a heating element, and calculates how much hot water (from a heat exchanger) or cold water (bypassing the steam boiler) it needs to add over the course of the shot to maintain the set temperature profi le. In the slight down profi le, the heat from the higher-temperature water is actually absorbed by the warming process, and by the time the microboiler begins to regulate temperature downward, it meets the rising gradient of the espresso and maintains temperature. PHOTOS BY MACIEJ OSTROWSKI

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