My evaluation process for a home espresso machine is similar to how I test standard drip coffee makers. First, I wash my hands and dry all removable parts and accessories. For most espresso makers, that includes a filter basket, metal portafilter inserts, water tank and so on. Next, I run a brew cycle with just hot water to flush out any remaining manufacturing material.
Most automatic espresso machines, except for the fancy super-automatic models, do not have an integrated coffee grinder And I prefer to test espresso machines with freshly ground coffee, not pre-clouded coffee, so I supply my grinder: 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 brew styles. That means it produces a grind of coffee beans that is pretty good. Second, its grinding size is consistently uniform. Both factors are key to a proper espresso brewing process.
To pull snapshots, I start with the suggested method outlined in a given machine's product manual. Usually, this includes the amount of coffee expected per shot, along with any guidelines regarding the level of coarseness. I also follow the save instructions (light, medium, or hard tamp) if the manual provides them.
Whenever possible, I drink double shots of espresso for all my tests. Be sure to record the weight of the grounds I use, plus the espresso weight 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 percentage extraction.
As with any coffee drink, 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).
Not many home espresso machines can prepare quality shots. This one was pulled from the Breville Barista Express.
If you overdo it, you risk releasing unpleasant flavors (bitterness) after the good. At the opposite end of the scale, under-extracted brews tend to have underdeveloped 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 needs to be concentrated. A great drip usually has a TDS percentage of 1.3% or 1.4%, a great espresso has a much higher percentage. For example, the Breville Barista Express produced shots with TDS percentages as high as 12.4%.
The recordings I pulled were balanced, with 18.6% extraction. The test coffee beans I use are the same variety I use for standard coffee makers – Costco's Kirkland Columbia. It's a medium-dark roast suitable for making espresso, too.
Many espresso machines have steam nipples for frothed milk. Breville Bambino makes steaming milk especially easy.
Lastly, I try my hand at milk with any coffee machine equipped with a steam wand. I record the entire steam wand experience, whether the process is premature, a chore, or somewhere in between.
You can use steamed milk to create espresso-style coffee drinks like lattes and cappuccinos.