I have recently come to know Miss Silvia. She’s from Italy, weighs a good 14 kg and even my wife welcomed her in our kitchen! As home brew espresso afficionados will know by know, I’ve become the proud owner of an espresso machine from Rancilio! She’s been around for a number of years, and is one of the most popular among prosumer espresso machines available before you take the step up to double boiler machines that allow simultaneous brewing and steaming. Every place that is (proud of) serving espresso uses these machines, but their price is well beyond most coffee lovers budget. The good news however is that even single boiler machines can produce excellent espresso!

The first time I offered the science of espresso any thought was when reading Jeffry Steingarten’s accounts of his espresso adventure (in “It must’ve been something I ate”) which brought him all the way to Italy and Illy and then back again to Manhatten where he set up 14 home espresso machines in his kitchen. This is also where I first was made aware of the fact that 7 g of coffee should be used for a single espresso (which is considerably more than the 5-6 grams found in the Nespresso capsules).

Since I decided to buy an espresso machine I have been devouring sites written by and for coffee enthusiasts: CoffeeGeek, Home Barista and Espresso! My Espresso! to mention a few. You’ll be surprised how much one can possibly write about espresso!

Considering the fact that there is a world championship for baristas, it might seem boisterous to claim that I have pulled a couple of decent espresso shots in the last few weeks. They certainly vary in quality, but by preparing and drinking espressos daily I learn more and more as I taste my way through different types of coffee. One thing I feel quite confident of is that preparing an espresso is the the most sophisticated extraction done in any kitchen. Consider these parameters:

coffee beans
roasting
grinding
dosing
tamping
water pressure
water temperature
extraction time
extraction volume

Luckily all of this has been researched in great detail and the last five generally should not be varied at all. To brew a perfect double espresso you should use water at 92-94 °C and a pressure of 9 bar. During an extraction time of 25-27 seconds you should get 60 mL of espresso – no more, no less! To provide enough back pressure you need to tamp the ground coffee relatively hard in the filterbasket. A pressure of 10-15 kg is recommended. As you can see all these parameters are fixed. So the only things left for the barista to vary is the grinding, the dose and of course the choice of coffee beans (including roasting). Since the recommended amount of coffe for a double espresso is 14-16 grams (some extend the range to 12-18 g), you’re basically left with grinding and the choice of coffee beans. Sounds simple, but there’s a lot that can go wrong. I’ll come back to all of this in part II. The espresso should neither be too bitter nor too acidic. And it should have a nice and stable crema.

“Crema, the dense, reddish-brown foam that tops an espresso, is composed mainly of tiny carbon dioxide and water vapor bubbles surrounded by surfactant films. The crema also includes emulsified oils containing key aromatic compounds and dark fragments of the coffee bean cell structure.”

There is one family whose name is forever linked to espresso – the Illy’s. The above quote is from Ernesto Illy’s article “The complexity of Coffee” which appeared in Scientific American, June 2002 (previously available from illyusa.com, now available through the internet archive – it’s highly recommended!).

The illy company was founded by Francesco Illy (1892–1956) in 1933. In 1935 he invented the precursor to espresso machines as we know them today. His son Ernesto Illy (1925-2008) studied food chemistry and worked with illy for his entire career. Francesco’s grandson Andrea Illy (1964-), also a chemist by training, currently acts as chairman of the board. “Espresso is a miracle of chemistry in a cup,” says Andrea Illy (this is as close to pure molecular gastronomy as you will ever get!). The (scientifically) interested reader will probably enjoy the definitive textbook on the subject: “Espresso Coffee: The science of Quality” which Andrea Illy has co-edited. The more artistically minded might prefer “Illy Collection: A Decade of Artist Cups”.

Further reading, listening and viewing
“Discovering La Dolce Vita in a Cup” (NY Times interview with Ernesto Illy from 2001). There is also a video interview with Ernesto Illy available on DVD, “The Complete Dr. Illy Milan Interview”.

Andrea Illy talked about “The Science of Coffee” at the New York Academy of Sciences (podcast) and was also interviewed by CoffeeGeek.

When it comes to preparation of espresso (which I will digg into in part II), “Espresso Coffee: Professional Techniques” by David C. Schomer is the standard textbook most people refer to, in addition to the videos “Caffe Latte Art” and “Techniques of the Barista”. Schomer developed Espresso Vivace with Geneva Sullivan and operates espresso bars in Seattle. The homepage features an extensive archive with articles on espresso by David C. Schomer.

Previous posts in the extraction series: water, ethanol and oil.