Wow, you’re really into this. Awesome. Make sure to check out the craft your own roast page here, now back to the brewing…
Coffee brewing is pure chemistry. The beans are a reactant, being prepared by being ground as consistently as possible to the desired surface area to volume ratio (SA:V). The duration of the reaction, how the reactants are mixed together, the temperature of the reaction, and if the product is filtered are chosen, the reaction occurs, and coffee is produced.
The assorted brewing methods through history are a selection of different values for each of the above stated parameters. Great news! Through history the optimal values for each parameter have been previously defined for each variant of the chemical reaction.
Let’s start with a little of the scientific theory behind brewing, and then talk about the categories of brewing methods.
Extraction: Different compounds in ground coffee have different solubility, meaning they dissolve into water at different rates. This differential solubility is what drives the ideal duration of the brewing reaction for a given grind size. Some soluble bitter compounds (Quinic acid, caffeine, furfuryl alcohol, trigonelline, etc.) occurring in roasted coffee beans have a lower solubility than the pleasant flavor compounds sought in the brewing process, meaning the reaction time should be limited in order to avoid over extracting these bitter compounds and altering the flavor compound distribution in the brewed product.
Scientific trials have shown that the ideal extraction (scientifically referred to as soluble yield) during the brewing of coffee is between 18% and 22%. Within this range, the ideal mixture of dozens of flavor and aroma compounds are dissolved, while excess dissolution of the bitter, lower solubility, compounds is avoided. Total soluble yield over or under this extraction target can result in:
- <18% - Not enough flavor (referred to as “under developed”)
- >22% - Over extracted coffee (bitter)
What other variables can affect solubility? The short answer is temperature, pressure, water pH, and existing soluble concentration in the water. Each of these variables must be considered while targeting ideal soluble yield during the brewing reaction. It is commonly known that solubility increases with temperature (although not necessarily equally for all compounds—leading to different flavors experienced at different brewing temperatures) as such, colder brewing processes require longer reaction duration for soluble extraction.
Scaa.org Standard for Brewing Coffee
Strength: The strength of coffee has to do with the concentration of soluble flavor particles. If an adequate mixing mechanism is employed during the brewing process, strength can be controlled by varying the amount of water and amount of coffee which are mixed together. The baseline ratio of coffee to water is 1:16 by weight, a range of target ratios are given along with strength and extraction goals on the table above.
Filters: All brewing methods have filters built into them in one way or another. The size of particles these filters allow into the beverage vary considerably across the different brewing methods. The particle size allowed through in a French Press is much coarser than a paper filter used in a Chemex brewer. This means that depending on the brewing method you select, and the associated ideal grind size for that method, some coffees can have a significant amount of finely ground coffee. These fines affect the texture (mouthfeel) of the coffee dramatically. It is truly up to our customer to determine their textural preference, and this may be the single biggest influence in the preferred brewing method.
Brewing method categories:
- Steeping Methods - The grounds are soaked in water for a given amount of time and then filtered. Steep duration varies with grind size. Ex. French Press
- Pour Over or Drip Methods - Water is run through the grounds, with the grounds usually held in place by a filter. Grind size, water flow rate, and temperature vary. Ex. Chemex, Percolator, auto-drip machine
- Pressure/Vacuum Methods - Pressurized water and steam are passed through grounds changing solubility characteristics. Temperature and pressure vary together, grind size is generally fine and extraction completed quickly. Ex. Espresso, Aeropress, Siphon
Each common brewing method belongs to one of these categories. The brewing methods we offer in the café at SyH Coffee bring a new aspect to the traditional espresso or drip coffee experience.
We can tell you theoretically which method has the most precise solubility dissolution profile; or which grinder gives the tightest particle size distribution; but who wants to make a decision about which coffee is their favorite the same way an engineer picks out a car?
We will leave the question of your preferences up to you, and promise to never give up on helping you continue discovering new and different ways to enjoy coffee.