What's in my cup?! Intro to Coffee Extraction

Coffee, duh.
Okay—but what else? What actually comes out of our beans and into our drink? And is it all tasty? Short answer: no. Longer answer: we’ve got you covered—and we’re going to keep it as digestible as possible.

Let’s start with our knight in shining armor: the number one thing most of us are searching for when we brew our cup. Yep, you guessed it—caffeine. You might also say “flavor” or “the color brown,” and you’d be correct. But what extract-ly is it?

Your cup is mostly water, plus a collection of all the parts of the coffee bean that are soluble. The maximum solubility of a coffee bean is roughly 28–32%. The rest—about 68–72%—is material that never dissolves in water (read: the grounds you compost or toss).

What ends up in your cup is some cumulative percentage of that maximum solubility. We call this the extraction yield percentage. We measure it as an average across the entire brew, knowing that each coffee particle interacts with water—and extracts—slightly differently.

What's not soluble? 

• protein
• fiber
• cellulose
• fat

What is soluble?

the bitters

• Caffeine <3
• Trigonelline - an alkaloid with positive aromatics. Helps form niacin (a B vitamin)
• Chlorogenic Acids (CGAs)- a collection of about 30 polyphenols with strong antioxidant capacity. Specifically formed from CGAs are chlorogenic acid lactones (quinides) and phenylindanes. 
  • Quinides - the key bitter component recognized in a medium roast coffees.
  • Phenylindanes - present in darker roasted coffees from the break down of caffeic acid during the heating process. They extract slowly in water and can be mitigated by controlling extraction. BE GONE BITTERS.
• Quinic Acid - contributes to coffees astringency and acidity.

the acids

• Citric acid – one of the most abundant organic acids in coffee. Levels depend heavily on cherry ripeness and sorting at the farm level. Think citrus 🍋
• Malic acid – the acid found in apples 🍏; a desirable, juicy acidity
• Tartaric acid – mostly degraded during roasting, but if present would resemble wine-grape acidity 🍇
• Phosphoric acid – increases during roasting and contributes a bright, sparkling sensation (not actual bubbles)
• Lactic acid – think sourdough bread 🍞. Produced during fermentation and associated with creamy, soft acidity
• Acetic acid – vinegar-like when excessive 😝. When fermentation is controlled, acetic and lactic acids enhance fruit perception; when uncontrolled, they show up as sharp and unpleasant

the sweets

• Sucrose – the primary sugar in green coffee. Most degrades during roasting, forming melanoidins through the Maillard reaction. These compounds contribute to body, color, and—yes—the brown stain on your white shirt that cold brew inevitably finds. While little sugar remains post-roast, good growing conditions and optimal ripeness still yield better-tasting coffee overall.

Soluble Extraction

solute + solvent = solution

During brewing, all soluble compounds left after roasting (the solutes) extract into water (the universal solvent) at different rates depending on contact time, temperature, and how they interact physically. What you’re left with is a solution.

First, we grind the coffee. Whole beans make water work extremely hard to penetrate the ~70% non-dissolvable structure to access the soluble compounds. Finer grinds increase surface area, giving water better access.

The catch? Particle size consistency matters. Uneven particles extract unevenly, and water always follows the path of least resistance.

Imagine water flowing through sand in a bucket—slow, lots of contact time. Now imagine part of that sand bed is tightly compact while another area is loose. Water will always pass through areas of low resistance first. That is an uneven flow of water with uneven contact time. This might become even more complex and hard to control with the addition of different-sized granules or the addition of large pebbles!

What's a good extraction?

An evenly extracted coffee tastes smooth, nuanced, and rich. It has pleasant acidity, integrated sweetness, and a long finish that makes you want another sip.

While extraction can be measured scientifically, we mostly judge it by taste—because taste rules.

Let’s say a roaster bags a coffee described as lemony. How we brew and extract the coffee will determine the experience of that flavor. 

• Under-extraction: Acids extract first. They’re lighter molecules and make up ~18% of soluble content. When dominant, coffee tastes grassy, vegetal, sour, or salty with a short finish. Think lemon juice with salt.

• Balanced extraction (18–22%): Sweetness and heavier compounds emerge, balancing the acids. Think lemonade—the lemon flavor shines in its best form.

• Over-extraction (22–24%+): Dry, hollow, bitter, ashy flavors dominate. Think lemon pith or over-steeped tea with a lemon twist.

How does it happen?

There are many variables that impact rate and quality of extraction. 

• Brew method

• Amount of coffee and water (usually helps determine a range of grind settings)
  

• Grind size (easiest to manipulate at home quickly)

• Brew time (often a result of grind size, brewing method dependent)

• Water temperature and quality (when you start out, this is great to hold constant)

• Roast level

• Coffee freshness

• Equipment quality and preparation technique

Why does any of this matter?

For Cafés & Roasters

• Enables more balanced, consistent coffee

• Supports effective dialing-in

• Helps identify equipment or coffee issues

For Home Brewers & Baristas

• Informs smarter purchasing decisions

• Helps troubleshoot brewing issues

• Builds appreciation for coffee’s complexity and value

• Encourages experimentation (it doesn’t have to be perfect)

Don’t Be Afraid to Try New Techniques!

Coffee is complex—but that’s part of the fun. It’s easy to feel overwhelmed by the variables, especially when you’re just starting to dig into the depths of da brew. Practice goes a long way.

And at the very least, you’ve got good coffee to get you started.