Prof. John Blackwell, Coffea Arabica Machina 101: PID, Part 1

This was dug up from the classic archives of Prof. John Blackwell, coffea arabica machina extraordinaire. An interesting read for those not familiar with or can use a refresher on the messy mechanics of how a PID controller works.

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THE DIFFERENCE BETWEEN PID AND THERMOSTATIC CONTROL SYSTEMS

by John Blackwell

In an espresso machine we have an electric heating element in water and we are trying to control a given setpoint (maximum achieved temperature).

The THERMOSTAT is an electromechanical switch trying to control the on/off cycle of the heating element in water. The thermostat can turn off the heating element at the exact setpoint, but the heating element is still hot (it can not cool instantly) and continues to heat the water causing a temperature raise above the ideal setpoint (the problem). So what to do? Position the setpoint lower so it turns off sooner then rises to the desired maximum. Oh great now, at least the water did not get too hot but it has to cool down to the lower setpoint before it will turn on. The best we can do now is to have a thermostat with a very narrow bandwidth (the difference between on and off setpoints) and hope for the best in our cycle of heating and cooling.

PID can be described as a set of rules with which precisely regulates a closed loop control system. In our heating element in water example, the PID predicts when to control the on/off setpoint, making corrections so the heating element does not under or over shoot the desired temperature.

How PID works without the math? Closed loop control system means a method in which a real time measurement of the process being controlled is constantly fed back to the controlling device to ensure that the value which is desire is, in fact, being realized. The mission of the controlling device is to make the measured value, known as the process variable, equal to the desired value, usually known as the setpoint. The best way to accomplish this task is to use the control algorithm known as PID.

In its basic form, PID involves three mathematical control functions working together. The most important of these, Proportional control (the P), determines the magnitude of the difference between the setpoint and the process variable (known as the error), and then applies appropriate proportional changes to the control variable to eliminate the error. Integral control (the I) examines the offset of the setpoint and the process variable over time and corrects it when necessary. Derivative control (the D) monitors the rate of change of the process variable and makes changes to the output variable to accommodate unusual changes.

Each of the three control functions is governed by a user defined parameter. These parameters can be adjusted to optimize the precision of control. The process of determining the values of these parameters is know as PID Tuning, or BIG MATH!!

GQ Ranks Top Cafes

GQ magazine showcases the top 10 places to get your daily fix in the U.S.

In “The Most Important Drink of Your Day“, GQ magazine hits home with the point that, “why pay $4.79 for a watery latte that was lovelessly made on a push-button machine that could be safely operated by a 4 year old?” (They’re referring to a superautomatic espresso machine, by the way)

In the “Golden Age of Coffee” (as they call it) that we now live in, “there’s now a wealth of coffee in America so rich and flavorful it’ll remind you why you originally fell in love with the stuff.”

Other than killer coffee and quality, what else do these featured coffee roasters have in common? They’re all customers of La Marzocco, of course.

Alterra
Blue Bottle
Caffe Vita
Intelligentsia
Kaldi’s
Ninth Street Espresso
Ritual
Stumptown
Verve
Zoka

Barista Round Table

Visions Espresso‘s Coffee Enhancement Lounge will be hosting the first of many Barista Round Tables. Bringing baristas and coffee geeks alike together to discuss coffee, methods, tools, machines, etc. and to build a stronger coffee community.

Mark your calendars, the first Barista Round Table will be held on October 28. PDF flyer is here:

Barista Round Table, pdf Oct.

What Can Be Better? Bikes and Coffee!

Mojo Bicycle Cafe in SF

Mojo Bicycle Cafe is a bike shop and coffee bar! Featuring a La Marzocco Linea pulling De La Paz‘ espresso. Also brewing Ritual on drip. They carry Felt, Swobo, Jamis, Rock Lobster, and Kona bikes. They pull a mean shot, especially for a place that’s not 100% specialized in coffee.

Bikes and coffee go very well together. We need more of these kind of shops people!

Four Barrel Coffee SF

Four Barrel Coffee's Mistral
Four Barrel Coffee’s Mistral

In Jeremy Tooker’s newest venture, he combined lots of wood furniture, open space, wall mounted dead animal heads, dedicated cupping table, and, of course, awesome coffee. All of this resulted in what’s commonly referred to as Four Barrel Coffee in the Mission district of SF. Recently, they have just turned one year old, and they are sure doing well, pulling kickass espressos on their double Mistrals. They roast onsite and, if you’re in town, definitely check them out! They are literally down the street from another seriously excellent roaster, Ritual Coffee.

Animal heads and lots of coffee. Is that a wet boar note I taste in the coffee?
Animal heads and lots of coffee. Is that a wet boar note I taste in the coffee?

Stumptown Producers Panel

Aleco and famers/exporters from Colombia, Kenya, and Costa Rica sitting across from baristas, shop owners, and consumers. Can the supply chain be any shorter than this?

Over the weekend, Stumptown Coffee Roasters hosted the Producers Panel, a presentation and discussion on the state of the coffee industry on the producers side. For those who have not had the opportunity to visit origin, this was a fantastic way to meet those responsible for their dedication and hard work on the other end of the supply chain. The panel took place at Seattle University, which was followed by a tasting of the coffee represented by the panelists at Stumptown’s nearby cafe & roastery. Coffees were enjoyed on the espresso machine (as single origin espressos), chemex, and pourover.

Even if you have been in the industry for some time (but haven’t visited origin yet), this has to be a sobering experience. In his own words, Ngatia, a coffee farmer from Karatina, Nyeri in Kenya, passionately spoke of how Stumptown and a small handful of other progressive coffee roasters are purchasing their coffees through the “second window” in Kenya’s coffee exchange. This enables him and his coop to receive up to twice as much for their above par quality coffees. Through their collaboration with Stumptown, Ngatia’s coop was able to increase their production by about 40% in the past couple years and is on track to almost double their current level in the coming year.

The farmers were very grateful for such progressive roasters to work with them via the direct trade model, and just as so for this opportunity to visit Portland and Seattle and meet those who enjoy their work. In fact, for most of them, this was their first trip outside of their respective countries.

This event has become an annual tradition at Stumptown. Hopefully, this will also be commonplace at other roasters as well.

Killer Latte Art from Intelligentsia LA

Nicelys amazing latte art
Intelligentsia LA’s Nicely (via his flickr page) steamin some amazingly well textured latte art. It seemingly defies laws of gravity and liquid cohesion/tension.
Another amazing latte art that defies gravity (and spillage) on Nicelys flickr page. Poured by Teal Allan.
Another amazing latte art that defies gravity (and spillage) on Nicely’s flickr page. Poured by Teal Allan.
Nicely at work.
Nicely at work.

Ok, I’m sooooo flying down to LA for coffee.

La Marzocco Wins Award

At Allegra Strategies’ 2009 European Coffee Symposium, La Marzocco S.r.l. was awarded Second Place in the “Most Innovative Product or Brand” category. Here’s a pat on the back, LM Italy!

What’s Next?

It’s been almost 3 years since Stumptown has opened their beautiful roasting facility and cafes in Seattle. No matter which roaster you work for or which coffee you prefer, it’s undeniable that Stumptown has had a profound influence over Seattle’s coffee scene. Without getting into who’s coffee is better and whatnot, it’s fair to say that everybody has been upping their game for sure. To that, more power to them all.

Stumptown Seattle's Mistral.
Stumptown Seattle’s Mistral.

This brings up an interesting question – with the proliferation of 3rd wave coffee, what’s next? 4th wave? What are the parameters of this next stage of evolution?

With the way things are brewing (bada bing!), direct trade and ultra attentive sourcing will result in brewing methods that highlight such extensive work. These may include single origin espresso and single origin coffees by the cup via various methods e.g. pourover, chemex, press pot, etc. Equipment-wise, this means new coffee brewers and espresso machines that enable greater control over soft preinfusion and pressure profiling. Though there has not been an entire industry consensus on merits or standards of soft preinfusion and pressure profiling (whether on a Mechanical Paddle La Marzocco, Synesso, or Slayer), things are trickling in.

Advanced soft preinfusion (soft preinfusion with pressure manipulation) in its various forms have shown what’s possible to date. It doesn’t necessarily work on all coffees and, in the end, it’s still in the tongue of the beholder. In words, it’s hella debatable! The results have been impressive for us – espressos tend to be much more softer and rounded, without sacrificing its core delicacies e.g. brightness, acidity, etc. Hopefully, as more advanced soft preinfusion machines (Mechanical Paddle La Marzoccos and Slayer) find their way onto coffee bars, a better consensus can result.

However, advanced soft preinfusion is but only an incremental step towards total control a.k.a. true pressure profiling (that is, infinitely variable pressure from zero to your desired maximum brew pressure throughout the extraction process). Whatever the technology (or the lack thereof) that will get an espresso machine there, more power to it. After all, it’s all about what’s in the cup that truly matters. Well, it’s also about reproducibility as well. It’s rather difficult to use either advanced soft preinfusion or pressure profiling to make every espresso shot in a busy cafe. It’s just not practical!

To date, no production machine has been able to truly enable true pressure profiling. To that end, La Marzocco is working on a brand new, true pressure profile machine. A prototype was shown at this year’s SCAA on a down low basis and there’s field tests/feedback going on to get maximum input and feedback from those that will ultimately use it. All we can say is, watch out for it in 2010!

Urban Coffee Lounge Rocks Coffee Fest

Congrats to Urban Coffee Lounge‘s Andrew and Laila on winning NWRBC 2nd and 3rd place, respectively! Andrew also won 1st place in Millrock’s Latte Art Competition.

Laila preparing drinks on a La Marzocco GB/5 at Urban Coffee Lounge. She came in 3rd place at NWRBC.
Burning through their Hairbender espresso from Stumptown.
Concrete fireplace. Now that’s urban.

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