Science of Coffee: Tasting Extraction

How grind affects flavor and why

featuring Renee Frechin | August 15, 2016
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What happens when water passes through coffee grounds? It’s the essential magic behind a great cup of coffee, the action that transforms beans into beverage. The chemical process that pulls flavors from coffee grounds and into water is called extraction, and understanding how it works can help ensure a balanced brew.

The Basics of Coffee Extraction

Approximately 30% of the organic material in coffee beans is water-soluble. When water is poured through grounds, it dissolves soluble material, drawing out flavors and aromas. Extraction can be affected by several factors, including time, water temperature, the ratio of coffee to water and the size of the coffee grounds.

We asked coffee master Renee Frechin, a chemist and 15-year Starbucks partner, to offer a quick lesson on extraction. The perfect expert for the task at hand, Renee has taught college-level biology and chemistry courses and is working toward her master’s degree in chemistry with a focus on food science. Watch as she conducts a simple experiment to show how extraction impacts coffee flavor, emphasizing the importance of using the proper grind for your brew method.

Getting the Rate Right

In coffee science terms, the rate of extraction refers to the amount of time it takes for water to pass through grounds. The goal is to make sure that the extraction rate lines up with the solubility rate to dissolve 18-22% of the coffee when you brew. The best way to accomplish that is by making sure that the size of your grind is appropriate for your brewing method.

Assuming your kitchen is not a chemistry lab, the best way to determine whether you’ve hit the target is to enlist your taste buds. Here is a quick guide to help you decide if you’re getting it right.

Finding the Grind

To find appropriate grind for your brewing method, think about brew time. A rule of thumb: finer grounds mean shorter brewing times. Espresso machines brew quickly, so a fine grind is best. Coffee presses require a coarse grind, while the Chemex® brewer works best at medium. Of course, those are just a few of the tools available for coffee lovers to experiment with at home. If you’re looking for advice on the best grind for a particular method, or you would rather have an expert grind your beans for you, a Starbucks barista can help.

Coffee brewing is a matter of art and science, with many variables at play in the pursuit of the perfect cup. Fresh coffee and quality water are the keys to successful brewing, but even the best ingredients need to be handled with care. Try conducting your own coffee science experiment to see how extraction affects your favorite blend.

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