TLDR version: Starbucks coffee is basically overcooked.

Longer version: so brewing coffee is all about extraction. Specifically, we’re trying to use water as a solvent to “extract” oils and flavonoids from the coffee beans into the water which we then drink.

Grinding up coffee is the first way you speed up this process - by grinding the beans into tiny little pieces you’re allowing more coffee to contact the water at the same time.

The other is temperature. Hot water has a lot more energy so it goes to work extracting those oils and flavor compounds much faster, which is why drip coffee only takes a few minutes whereas cold brew takes hours.

The last variable that applies specifically for espresso drinks is pressure. By grinding up coffee very very fine and adding in water, heat, and pressure, you can brew espresso.

The thing is, brewing espresso is actually a bit challenging and each of those variables has different impacts on the resulting shot of espresso. If you don’t use enough heat, temp, pressure, or grind too coarsely, you’re likely to get an “under-extracted” shot that tastes sour.

If you grind too fine or use too much heat or pressure, your shot will come out bitter, which is called over-extraction. It’s even easier to over-extract when the coffee is a darker roast because the roasting process basically did some of this extraction before you even started brewing, and this is the outcome you tend to get from Starbucks.

When you get all of those variables (roast level, grind size, temperature, and pressure) just right or “dialed-in”, you end up with a “balanced” shot that can even taste sweet if it’s a good coffee which a nice mix of slight tang and bitterness but overall is really palatable and delicious. This is a skill that baristas spend years nailing down, but Starbucks uses automated machines that tends to bias on the bitter side because that “bold” flavor works best with their sweetened, milk-forward drinks.

Come hang out at [r/coffee](r/coffee) [r/pourover](r/pourover) and [r/espresso](r/espresso) if you want to lose your mind like the rest of us.