What's in my cup?! Intro to Coffee Extraction
What's in your cup? Coffee, duh. Ok, but what else...what comes out of our beans and into our drink. Is it all tasty? We have some answers for you. And we are going to make it as digestible as possible.
Let's start with the our knight in shining armor - the number one thing most of us are all searching for when brewing our cup. Yep, you guessed it. CAFFEINE. So, that's one thing in our cup. You might say, "flavor" or "the color brown" and you would be correct. But what extract-ly is it?
Your cup is mostly water with a collection of all of the parts of a bean that are soluble. The maximum solubility of a coffee bean is roughly 28-32%. The rest (approximately 68-72%%) is the mass that never disappears because it isn't dissolvable in water (read: the grounds you throw away or compost with). The part that winds up in your cup is some cumulative percentage of the maximum solubility; we can refer to this as the extraction yield percentage. We look at this percentage as an average for the entire brew, understanding that each ground particle will interact with water and extract differently!
What's not soluble?
What is soluble?
- 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. Reminiscent of the taste of aspirin.
the (sour) acids
- citric acid - one of the most abundant amongst the 38 organic acids in coffee. The amount of this is influenced by how well-ripened and sorted the coffee cherries were at the farm level. think citrus 🍋
- Malic acid - think the type of acid present in apples 🍏 this is a desirable fruity acidity.
- tartaric acid - most of this acid disappears during the roasting process. but if it WERE in larger percentages and identifiable on the palate, it would be like wine grapes 🍇
- phosphoric - an acid that increases during the roasting process. It's the same acid in soda that has that sparkly feel - not the bubbles though.
- lactic acid - think sourdough bread🍞it's what shows up during fermentation, like in kimchi and sauerkraut. Lactic acid bacteria live on the outside of many fruits and vegetables and they just so happen to cohabitate with acetic acid bacteria and yeast on the outside of coffee cherries.
- acetic acid - yummy. During fermentation, yeast feed on the natural fruit sugars and they produce alcohol as a by product. Then the acetic acid bacteria feed on the alcohol and form acetic acid. What does it taste like? Vinegar! 😝 Good news, when fermentation is controlled and positive, acetic and lactic acid help the perception of perceived fruitiness. When uncontrolled or over-fermented, it can show up as very sour, bleh.
- sucrose - saccharides! that's where the sweetness comes from but, alas, roasting degrades most of this. The degradation of sugars forms melanoidins during a process called the Maillard Reaction (my-yard...like, uh, "my milkshake brings all the boys to my-yard") Anyway, these little melanoidins are mostly responsible for that body-yody-ody-ody possible in your cup and they are most definitely the cause of the brown stain on your white t-shirt that you thought you wouldn't splash your cold brew on. While there might not be much sugar content left, we do know that the creation of sugars during optimum ripening and good growing conditions yields the BEST tasting coffees.
solute + solvent = solution
During the brew process, all of the compounds left after roasting that are soluble (the solutes) will extract in water (the universal solvent) at different rates due to the contact time, temperature, and facet in which they interact. What you are left with post-combo is a solution. Usually, the solution to my daily migraine 😉heh heh heh *insert your laughter here*
Uncovering the buried treasure:
First, you have to grind the coffee. When the beans are whole, it makes water have to work REALLY hard to penetrate the 70% non-dissolvable matter to get to the soluble stuffs. The finer you grind, the more access water has to this content.
The catch is that the sizes of the individual particles need to be consistent so that you have an even extraction AND the water needs to be able to completely and evenly saturate each section of your coffee bed. A little easier said than done.
Imagine water passing over sand in a bucket. Slow right? A lot of contact time? Now, imagine that one side of that sand bed is really compact and dense - all of the water would flow through an area with lower resistance or with pockets of air and then part of the sand might not even get fully wet! Imagine, alternatively, that in this bucket there are also giant pebbles. Water would flow around those rapidly, with very little contact! That doesn't sound very even, right? This, my friends, is a huge factor in considering why your coffee might taste off.
What's a good extraction?
Balance, balance, balance. And balance is what we look for in evenness. An evenly extracted and balanced coffee tastes smooth, nuanced, rich. It has pleasant acidity and a long finish that makes you want to take another sip.
We mostly decide by taste. Cause taste RULES. And you will adjust multiple variables accordingly, all lending to either more extraction, less extraction, or balanced extraction. As a general concept, imagine that the roaster bagged a coffee that had the flavor of *lemons* - keep this in mind as you continue reading.
Acids extract first. They're molecularly light and make up around 18% of the soluble content. They taste grassy, vegetal, sour, salty, and present a flat, quick finish when making up the majority of a cup. Think lemon juice mixed with salt. We can't appreciate the floral and citrusy flavor of the roast, because the taste is overpowering.
With more extraction, the heavier compounds come out. Perceivable sweetness and smooth tastes become present around 18-22% extraction. The compounds and dilution taking place create balance to the acids. Think lemonade. The flavor is now highlighted in its best format.
With too much extraction, usually over 22-24%, that taste becomes unbalanced again. Drying, hollow, ashy, bitter. Like someone put a cigarette in your lemonade. BUERK.
How does it happen?
Depends on the brew method, for one. The brew method will influence how coarse or fine you can grind, how quickly you can brew, and how much coffee or water you can prepare. It will determine the amount of energy applied to the slurry of coffee and water.
It depends on the water temperature, as certain compounds are released in higher temps. It depends on your water quality. It depends on the roast degree, coffee quality, and coffee age. It depends on the quality of your equipment, your preparation and technique, and much more. We can dive into that on another day!
Why does any of this matter?
For advanced and dedicated cafes/roasters.
- helps to know how extraction works so we can serve more balanced coffees. We manipulate variables that speed up, slow down, or change extraction during a process called "dialing-in" - this process can happen all day long with small adjustments every few shots.
- helps achieve consistency
- helps detect issues with coffees or equipment
For the at-home enthusiast or barista
- knowing what changes during the roasting process can help make informed purchasing/selling decisions
- knowing what extracts when can help you make adjustments to your coffee quality! it doesn't have to be perfect, but it is fun to experiment.
- knowing coffee complexities helps you appreciate product value
Don't be afraid.
Coffee is complex, for sure. And it is easy to feel overwhelmed by all of the variables that influence your brewing experience; especially if you're just now diving into the depths of da brew. No worries, practice is key. And, at least, you have good coffee to get you started :)