The Science of Coffee Extraction: Grind, Temperature, and Yield

Coffee tastes complicated because it is complicated. A single roasted coffee bean contains over 1,000 volatile aroma compounds. Brewing extracts some of them, but not all of them, and the order in which they dissolve matters as much as which ones end up in your cup.

The Specialty Coffee Association spent years developing a framework for coffee extraction that explains why the same beans can produce a sour cup, a balanced cup, and a bitter cup depending on nothing more than grind size and temperature. That framework is straightforward enough to apply at home.

The Extraction Sequence

Coffee compounds don’t all dissolve at the same rate. They extract in a rough order based on their solubility and the energy required to pull them from the ground coffee particle.

The first compounds to dissolve are the fruity organic acids: citric, malic, acetic, and others. They’re highly soluble and extract quickly. This is what you get in the first 20-30% of the brew time.

After the acids come the sweeter, mellower compounds, including certain sugars from the roasting process (not sucrose, which has been destroyed by roasting, but caramelization products), along with desirable bitter compounds from caffeine and some chlorogenic acids. This middle zone is where balanced coffee flavor lives.

In the final stage, harsher bitter compounds and dry, astringent molecules dissolve. These are the compounds you want to minimize. They’re harder to dissolve but they’re there, and if you extract too long or too hot, you pull them out.

Think of it like making tea from a bag. The first minute is mellow and sweet. The fourth minute is tannic and bitter. The chemistry is different but the principle is identical: time and temperature determine how far down the sequence you go.

What Extraction Yield Means

Extraction yield is a ratio: the mass of coffee solids that ended up in your cup divided by the mass of dry grounds you started with, expressed as a percentage.

At 18-22% extraction yield, you’ve dissolved the acids and sweet compounds without going too far into the bitter zone. The Specialty Coffee Association defines this as the “ideal extraction” range. Below 18%, you’ve mostly extracted the acids and left the sweeter compounds behind. The coffee tastes sharp, sour, and hollow. Above 22%, you’ve pushed into the bitter zone. The coffee tastes harsh, dry, and astringent.

You can’t easily measure extraction yield at home without a refractometer (a device that measures dissolved solids in liquid). But you can tune your process based on the taste feedback.

Sour and thin = under-extracted. Go finer on the grind or increase water temperature. Bitter and harsh = over-extracted. Go coarser or decrease temperature.

Grind Size: Surface Area Controls Rate

Grinding coffee creates surface area. Water can only extract compounds from the surfaces it contacts. Finer grinding means more surface area per gram of coffee, which means faster extraction.

This is why espresso uses a fine grind with a short brew time (25-30 seconds), while French press uses a coarse grind with a long brew time (4 minutes). Both can hit the same extraction yield, but they do it with different surface areas and different contact times.

A coarser grind isn’t just slower, it’s also less even. Coarse particles have more internal material that water has to work harder to reach. This is why grind consistency (evenly sized particles) matters almost as much as grind size. Cheaper grinders produce more “fines,” very small particles that extract very fast and become bitter before the larger particles have finished extracting. This is one reason a burr grinder produces more consistent results than a blade grinder.

Water Temperature: Energy Drives Dissolution

Water temperature determines how quickly compounds dissolve and which ones are soluble at all. Higher temperatures give water molecules more energy to break apart coffee’s cellular structure and pull compounds into solution.

The 195-205°F range is the sweet spot for most brewing methods. Below 195°F, extraction is slow and tends to stop before you reach sufficient yield. Above 205°F, you extract bitter compounds faster and risk bringing out astringent molecules at higher concentrations.

Boiling water (212°F at sea level) isn’t a disaster. The difference between 205°F and 212°F is small, especially since the water drops in temperature the moment it contacts room-temperature grounds. But using off-the-boil water (letting boiled water sit for 30-60 seconds) gives you slightly more control.

Cold brew operates on a completely different logic. Using cold or room-temperature water means extraction is slow and primarily captures the most soluble, least bitter compounds. The long steep time (12-24 hours) compensates for the low temperature. The result is coffee with different chemistry than hot brew, not just cold hot coffee.

The CO2 Problem and Why You Should Bloom

Fresh-roasted coffee contains significant dissolved CO2 that was produced during roasting. When hot water hits the grounds, this CO2 escapes rapidly, forming bubbles. Those bubbles physically block water from making contact with the grounds evenly. The result is channeling: water finds paths of least resistance through the bed and over-extracts some areas while under-extracting others.

Blooming solves this. Add a small amount of hot water, just enough to wet all the grounds, and wait 30-45 seconds. The bulk of the CO2 escapes before you add the rest of the water, leading to more even and consistent extraction.

The bubbly, dome-like expansion you see during blooming with fresh coffee is CO2 releasing. Older, stale coffee doesn’t bloom much, which is actually one of the easiest indicators of how fresh your beans are. The flavor connection between freshness and extraction efficiency is direct.