CAMBRIDGE -- Posted at Simon's Coffee Shop in Porter Square is a list entitled ''Fifty things to improve your espresso production." Written by Nick Cho, a revered Washington, D.C., cafe owner, it includes everything from the easily understood (''use fresh beans") to coffee-geek technicalities (''insert the portafilter with enough torque to create a good seal with the portafilter gasket").

The list hangs on the shop's La Marzocco machine, but not where the espresso-drink makers -- called baristi, Italian for bartenders -- can see it. They don't need to, because they have manager and lead barista Jaime van Schyndel reminding them about such things on a daily basis. The list instead faces customers, as a way of reminding them just how tricky truly excellent espresso can be to achieve.
''I'm trying to change what it means to be a barista in this town," van Schyndel says, pulling two double shots for a visitor. ''It takes skill, it takes knowledge, and it shouldn't just be someone who happens to work behind a counter in a coffee shop."

All this is about as new to van Schyndel and Simon Yu, the cafe's owner, as it is to much of the Northeast, which as a region is just starting to get a handle on espresso. Compared to Seattle, Vancouver, or any number of cities in Italy, Denmark, or elsewhere in Europe, what passes for the real thing in Boston and even New York City has often been weak, burnt, bitter, watery, or some combination thereof.

Starbucks may be responsible for the growth in espresso consumption and awareness in the United States, but purists fault it for miseducation. Unlike the shots usually served by the Seattle-based behemoth, good espresso should be deeply flavored but smooth enough to be drunk unadulterated by sugar or even milk, and boasting a thick head of ''crema" produced by an emulsification of the oils in the beans.

''I could talk for hours about Starbucks," van Schyndel says.

Some critics would go so far as to say that the company's drinks, let alone those now coming out of local favorite Dunkin' Donuts, barely even qualify as espresso.

''Espresso has a pretty bad rap in most of America,"

Ken Nye, owner of Ninth Street Espresso in New York City, says over a macchiato (espresso with a dab of steamed milk on top) at his far-East Village shop.

' 'They haven't had it. They've had this abomination."

Pardon the pun, but changes are brewing, slowly but surely. In both Boston and New York, espresso fanatics can find pockets of quality like Simon's and Ninth Street, where trained, dedicated baristi are grinding, dosing, tamping, pulling, and frothing. At these cafes, the point is to emphasize the unique flavors that can result when hot water pushes through finely ground coffee at the right speed.Continued...

''Good espresso should taste almost like freshly ground coffee smells," says Nye. And its velvety, full-bodied texture should coat the palate.

There are so many steps to achieving this, and virtually no room for error when making something with only two ingredients: coffee and water (plus milk for cappuccino, latte, or other espresso drinks). The size of the grind, the pressure and technique used when ''tamping" them into the machine's portafilter, and the temperature of the water are among the factors that can affect whether the water presses through in the requisite 20 to 30 seconds for 2 ounces of liquid. Faster or slower, and it's thin and sour or burnt and bitter.

Much of the strategy involves freshness. The best espresso, Nye says, comes from coffee roasted recently and preferably locally.

''Coffee doesn't travel well," he says. ''If coffee gets up to 112 degrees in the back of a truck, you've basically killed it."

Even before then, of course, there's the source of the green, unroasted beans, something that coffee guru George Howell has focused on with his Acton-based Terroir Coffee, which sources out single-origin beans and roasts them lightly. Van Schyndel, who says,

''I'm not a George Howell apostle,"

nonetheless uses Terroir at Simon's and praises the particular flavors that different beans and different roasting techniques can bring to a cup. The barista gets together with other coffee-focused friends every weekend for tastings called ''cuppings."

Unlike Ninth Street's dark-roast blend, which tastes particularly chocolatey, the much lighter roast that Terroir applies to its Daterra beans from Brazil brings out their sweetness and mild acidity.

''The thought that it needs to be a dark roast is the biggest misconception in espresso, and the second biggest is that espresso should be a blend," says Peter Lynagh, Terroir's quality control supervisor and a trained barista. ''It's absurd."

The dark-roast standard, Lynagh says, stems from decades ago, when the raw coffee available in the United States and Europe was of a much poorer quality.

''If you have an unripe coffee or a robusta coffee," Lynagh says, referring to a particularly harsh variety, ''the further you roast it, there is a point where it does become more pleasant."

Now, when companies like Terroir are dealing with ''super high-quality rare boutique lots, we would be nuts to go past a medium roast with it," he says.

''Where coffee is really now becoming most intriguing and alluring is at that medium- or light-roast level. This is the cutting edge."

Aficionados like van Schyndel, Nye, and Lynagh talk about coffee the way sommeliers talk about wine, describing ''notes" of caramel, citrus, nuts, and chocolate. But one stark difference between the two is that after production, wine is sealed up in bottles to be enjoyed in the future, not right now. In fact, among the theories about the derivation of the term espresso is not just that it means ''fast," but that it comes from the Italian word espressamente, meaning expressly for you, or made to order.

As Stefania Cocozza, district sales manager for illy caffe North America, put it at a customized barista-training session for me in New York,

''You can have the best coffee in the world, but if you don't know how to brew it, forget it."

Nye, whose Ninth Street Espresso was an anomaly when it opened five years ago, says good baristi cringe when they see the missteps. At the top of his red-flag list are places that aren't grinding beans on demand for each shot, whose equipment is dirty, or who are trying to automate some aspect of the process in a way that prevents making necessary adjustments.

''If you're getting one of those things wrong, I'm willing to put cash on the table that you're getting a lot of them wrong," Nye says. ''When I see things like that, I order tea. And I don't even like tea."

When things are done right, Nye orders a double espresso or a macchiato, which he and many other purists prefer because it doesn't hide the espresso with the taste of milk. But plenty of others love their cappuccinos and lattes, which in the right hands combine the espresso with ''texturized" milk, which turns a little sweet when properly heated. (Customers who order their espresso drinks ''extra hot" are missing out on this phenomenon.)

And then there's so-called latte art, in which the milk is poured in such a way that it combines with the crema to create a design, a particular point of pride among skilled baristi like van Schyndel, who took third place in a latte art competition in Washington, D.C., this year. But it's not just for aesthetic display. Latte art shows that the espresso and milk were both prepared at least somewhat properly.

Artistic or not, even places with the best reputations for espresso preparation don't always measure up, which shows just how important the individual barista can be. On an espresso tour of New York recently, I trekked out to Brooklyn to the acclaimed Gimme! Coffee, which roasts its own beans and is considered among the handful of top-quality espresso bars in the city. But the barista let the shot run far too long, resulting in a light crema and a sharp, bitter brew.

At Joe the Art of Coffee on 13th Street in Greenwich Village, when manager Erin Meister (also a writer who sometimes freelances for the Globe) jumped behind the bar to show me what the place could do, she had a hard time pulling a shot that satisfied her. It was partly because the grinds were set to the particular tamping pressure of barista Amanda Byron, and partly because the machine's pressure kept changing. So we went to the cafe's Waverly Street location, where barista Drew Victor, who came to New York from Cafe Fiore and Victrola in Seattle, pulled a smooth, rich, dark shot.
When Meister's co-workers heard we were planning to end our tour at a Starbucks, barista Susie Ross said,

''Don't the machines do everything now? They just push a button. Creepy."

''Some of them do," Meister replied. ''But some of them have Marzoccos. They just don't know how to use them."

Indeed, when we walked under the famous green-and-white logo on a nearby corner, there was no grinding, dosing, or tamping in sight, just a big machine and two workers pushing buttons and waiting. We ordered a double espresso and a macchiato, and the shot's nearly white, thin crema dissolved immediately. It had the consistency of drip coffee, with virtually no body and little flavor other than a bitter bite.

We couldn't add the sugar quickly enough.