My evaluation process for a home espresso machine is similar to how I test standard drip coffee makers. First, I hand-wash and dry all removable parts and accessories. For most espresso makers, that includes the filter basket, metal portafilter inserts, water tank and so on. Next, I run one brewing cycle with just hot water to flush away any residual material from manufacturing.
Most automatic espresso machines, save for fancy super-automatic models, lack an integrated coffee grinder and I prefer testing espresso machines with freshly ground coffee, not preground coffee, so I supply my own grinder: the Breville Smart Grinder Pro. I chose this conical burr grinder for two reasons. First, it's calibrated more for espresso than for drip or other brewing styles. That means it produces a coffee bean grind that's quite fine. Second, its grind size is consistently uniform. Both factors are critical for a proper espresso brewing process.
To pull shots, I start with the suggested method outlined in a given machine's product manual. Usually that covers the amount of coffee grounds expected per shot, along with any guidelines regarding coarseness level. Likewise, I follow tamping instructions (light, medium or hard tamp) if the manual provides them.
Whenever possible, I brew double shots of espresso for all my test runs. I make sure to record the weight of the grounds I use, plus the weight of espresso for each shot I pull. This data, along with readings from a portable refractometer, allows me to calculate two important percentages: total dissolved solids and extraction percentage.
Just as for any coffee brew, the ideal extraction percentage for espresso is a range between 18% and 22%. This yields a balanced cup, assuming you perform an even and efficient extraction of coffee compounds from your grounds (both flavor and caffeine).
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Not many home espresso machines can brew quality shots. This one was pulled from the Breville Barista Express.
Tyler Lizenby/CNETIf you over-extract, you run the risk of leaching out unpleasant flavors (bitterness) after the good. On the opposite end of the scale, under-extracted brews tend to have undeveloped flavors. Lacking sugars and other caramelized organic chemicals, these shots will taste sour, weak and watery.
Unlike a cup of drip coffee, barista-quality espresso should be concentrated. Excellent drip typically has a TDS percentage of 1.3% or 1.4%, great espresso has a much higher percentage. The Breville Barista Express, for example, produced shots with TDS percentages as high as 12.4%.
The shots I pulled were balanced, with an extraction of 18.6%. The test coffee beans I use are the same variety I employ for standard coffee makers -- Costco Kirkland Colombian. It's a medium-dark roast suitable for brewing espresso as well.
Many espresso machines have steaming wands for frothing milk. The Breville Bambino makes steaming milk especially easy.
Brian Bennett/CNETLastly, I try my hand at milk frothing with each coffee machine equipped with a steam wand. I record the overall experience with the steam wand, whether the process is a snap, a tricky chore or somewhere in between.
You can use steamed milk to create cafe-style espresso drinks like lattes and cappuccinos.
Brian Bennett/CNET