What Makes Starbucks' Universal Grind Unique
When it comes to convenience, Starbucks is looking out for you, even when it comes to the universal grind of their bagged coffee grounds. Grind sizes are one of those coffee things that can be a real headache to deal with at home. Which grind size works best in which circumstance isn't common knowledge for most casual coffee drinkers, and getting the precisely right grind requires special equipment most people don't have and don't want to buy. With the proliferation of different home coffee-making tools like pour-overs and French presses, this has even become a problem for pre-ground coffee, because the grind that worked in the older days of mostly drip coffee can taste pretty bad when used with other modern methods. That's why Starbucks has a universal grind.
Starbucks' universal grind is formulated to hit a sweet spot that gets the best results with a number of popular brewing techniques. It's the grind it uses both in stores for its standard drip coffee and in its store-bought pre-ground coffee. It's a medium-course grind, which means it can work with French press, percolators, and drip coffee machines. While it's not ideal for pour-over, that method is adjustable enough in how you brew that it can still work, making the universal grind good for pretty much all of the most common ways people make coffee at home.
Getting the best flavor from coffee grounds is all about a process called extraction, or how the length and intensity of the coffee's exposure to water will draw flavor from the beans. When choosing a grind, you need to find the level that will result in a perfect balance between over and under-extraction, as both extremes can result in poor-tasting coffee. Under-extracted coffee can taste sour, while over-extracted coffee is bitter and one-note in flavor. Coffee can be under-extracted if it is too coarse and not enough surface area is exposed to the water, but even coarse ground coffee can end up over-extracted if your water is too hot, or you leave it brewing for too long.
The reason Starbucks' universal grind goes to medium-course is that most of the more popular methods of home coffee brewing involve longer water exposure, so a fine grind would result in an over-extracted cup. French press immerses coffee for up to four minutes, and drip coffee makers that make bigger batches of coffee need a more coarse grind so cup after cup of water can keep flowing through. While it's impossible to find one grind that works with everything perfectly, medium-coarse hits a middle ground that works with these popular methods well enough to be "universal."