Coffee Foundations: Extraction and TDS
Have you ever made a cup of coffee that just doesn’t taste right? Maybe bitter and leaves your mouth feeling dry, or sour and papery? Or a coffee that tastes good but is too heavy or too thin? This doesn’t necessarily mean that the coffee you are using isn’t great, but does mean that there are things you can change about the way you’re brewing the coffee to make it a more enjoyable cup. The things we’ll be looking to change are the extraction of the coffee as well as the strength that we're brewing it at.
Strength (TDS)
Strength refers to the TDS - or Total Dissolved Solids - in a cup of coffee. It affects how heavy or light the coffee feels as you sip it and makes the difference between a cup of coffee that feels full - or just a hot cup of brown water.
The strength of the coffee you drink is affected by how much water you use to brew - relative to the amount of ground coffee you use. A common starting point for brewing coffee is 1 gram of ground coffee to 16 grams of water. This results in a balanced cup that is not too thin and not too heavy, but you should play around with your coffee to water ratio to find what strength you enjoy most!
Lower ratios of water to coffee generally result in more complexity in the coffee, sometimes to a point where all of the flavors taste jumbled together - even a bit muddy. Higher ratios of water to coffee will tend to result in a more clear and clean cup of coffee - but can also make the coffee tastes watered down, losing a lot of the mouthfeel you would have at a lower ratio. (Relative to cooking - making a stock using a lot of water will result in a clean and light broth. Reduce it down, and the flavors become much more concentrated with less liquid.)
Extraction
Extraction refers to how much of the flavor compounds found in coffee beans have been pulled out of the ground coffee and end up in your cup. This changes the flavor profile of your cup of coffee, making the difference between a bitter, dry cup of coffee - sour, papery, and slightly vegetal cup - or a balanced, sweet, and round coffee that you can’t stop sippin’. Extraction works somewhat in layers: first comes acidity, then sweetness, then bitterness. The key is to find a balance of these three.
Under- vs. Over-Extraction
Less than ideal coffees usually fall into one of two categories: under or over - extraction.
Under extraction means that in the brewing process we haven’t quite pulled out all of the flavor compounds that we want from our coffee. These beginning flavors that we get from coffee are usually on the sour and acidic end of the spectrum - and with under extraction - we pretty much only took those acidic flavors from the coffee by the time we’re done brewing. The coffee is lacking in sweetness and any pleasant bitterness.
Over extraction means that we have pulled a LOT of flavor compounds from the coffee, to the point where we are getting undesirable tastes. We’ve taken so much from the coffee grounds that the bitterness of the coffee is overwhelming the earlier layers of extraction - the acidity and sweetness.
Image from Mistobox
Finding your ideal brew
What can we do to help get a good tasting, well extracted cup of coffee?
The main things we can change to affect extraction include:
Water and coffee contact time
Grind size
Physical agitation of the coffee grounds
Water temperature
Water and coffee contact time
This is the big one! Most of the other variables to change have a direct impact on the time that we need the water and coffee to be in contact with each other. But we can also change this variable by itself in a few specific instances.
In something like a French press where the coffee is more or less “steeping” in the water - the amount of time you let the coffee “steep” in the water has a large impact on the taste. Steep for only 1 minute - and the coffee may taste thin, hollow, and sour - under extracted. Steep for 20 minutes - and the coffee will be heavy, overwhelmingly bitter, and dry - over extracted. Find a happy medium and the result is a balanced, sweet, and full coffee.
Grind size
Make the grind size smaller, and those tiny particles have a much easier time getting their flavor compounds pulled out by the water. Make them larger, and it makes it more difficult for the flavor to be brought out of the coffee. We can think about coffee and water like different sized sponges. Take a tiny piece of a sponge and a drop of water may saturate the entire sponge. With a large sponge, one drop of water will barely saturate the surface.
Picture the coffee in a French press again, and lets say we’re doing a 5 minute steep of the coffee. A very small grind size will make it so the water very easily pulls out all of the flavors from the coffee in those 5 minutes - resulting in a bitter and dry coffee (over extracted). A very large grind size for those same 5 minutes will make it so the water has a hard time getting all of the flavors out of the coffee - leaving you with a thin, vegetal, and sour coffee (under extracted). Find the right grind size, and in those 5 minutes the coffee ground will have been extracted just right - leaving you with a great coffee.
Water temperature
An easy way to think about this one is comparing the time that is needed to make cold brew versus any hot cup of coffee. Cold water has a much harder time drawing the flavors out of coffee, whereas very hot water has a much easier time. With cold brew for example, using room temperature water to brew the coffee means that we have to steep the coffee for anywhere from 18 to 24 hours. With any coffee brewed with hot water, there are rarely times when a brew has to last longer than 10 minutes. Steep coffee with ice cold water for 12 hours and the coffee may be sour, vegetal and under extracted. Steep for 12 hours with boiling hot water, and the result will be extremely bitter, dry, and over extracted. Find the right water temperature for a balanced and sweet coffee!
Physical agitation of the coffee grounds
Something like stirring the coffee grounds in a French press or AeroPress will directly affect the extraction of your coffee. Stir the coffee grounds for a second or two, and extraction might be boosted a small amount if we have a 5 minute brew time. Stir the coffee for 2 minutes, and the extraction of the coffee will increase a drastic amount, and lead to over extraction given the same 5 minute brew time. Finding the right amount of agitation will boost the extraction level just the right amount if some of the changes you’ve made up to this point haven’t gotten the coffee to where you’re happy with it!
Believe it or not, this is just scratching the surface of extraction! But, it should give you the tools to help out and get your cup of coffee to a great place. Espresso extraction follows the same general rules, but also has a few more added variables. Keep an eye out on our blog to see when we post a guide for at home espresso!
Having trouble dialing in your morning cup? Need some guidance for a specific brewing method you’re using, or have an amazing recipe you’d like to share? Reach out to us at talk@defer.coffee to continue the conversation!
