Brew Theory

Last updated 05/19/2023

Brewing specialty coffee can be an exciting new hobby that can be complex but can also be made very simple. It requires an understanding of the brewing process, the coffee itself, and the desired flavor profile. 

To understand brewing theory fundamentals, we’ll begin by exploring the concept of extraction and the effects it has on flavor.


Extraction is the process of dissolving the soluble compounds found in coffee, such as caffeine, acids, and oils into water. During extraction, the water extracts different compounds in a particular order. This is based on the compounds solubility and molecular weight. The rate and extent of  extraction is influenced by factors such as the brewing method, water temperature, grind size, coffee to water ratio, and contact time. 


Flavor has an immense amount of complexity and is completely subjective. This is influenced by the combination of taste, aroma, body, and aftertaste. With taste, think of the five basic tastes: sweet, sour, salty, bitter, and umami. Aroma refers to the volatile organic compounds that are released during the brewing process and affects smell. Body is equal to the mouthfeel/texture which ranges from light to heavy. Aftertaste refers to the lingering flavor and mouthfeel that remains after you’ve swallowed the coffee. 

Our overall goal is to achieve a cup that highlights the unique characteristics of the coffee but to keep balance at the forefront. 

Under-extracted coffee will taste sour, acidic, and thin, while over-extracted coffee will taste bitter, astringent, and dry. Ideally, you want to extract enough compounds to achieve a full and complex flavor, without over-extracting and ruining the taste.

To achieve this balance, you need to understand how different factors affect extraction and flavor. For example, a higher water temperature will increase the rate of extraction, but also increase the likelihood of over-extraction. A coarser grind size will decrease extraction and produce a lighter-bodied coffee, while a finer grind size will increase extraction and produce a heavier-bodied coffee. A longer brew time will increase extraction, but also increase the risk of over-extraction.

In conclusion, understanding extraction and flavor is essential to brewing specialty coffee that tastes great. By experimenting with different brewing methods, water temperatures, grind sizes, coffee-to-water ratios, and brew times, you can learn how to extract the best flavors from your coffee. 

Understanding coffee characteristics 

Origin: Country and region the coffee was produced and processed.

Processing: Method in which the cherry skin, fruit and mucilage is removed. The method in which the coffee beans are dried is also a part of processing. 

Elevation: This is the elevation in which the coffee is grown and cultivated. Generally, the higher the elevation the denser the coffee can be. 

Varietal: The arabica species has many sub-species that are cultivated for specific environmental conditions. 

Roast Level: This can be determined in various ways. An Agtron can measure roast level in color, development/overall roast time can give some insight, and also just using your own observation.



Advantages and disadvantages of cone vs flat brewers

Cone brewers will inherently have mixed extraction by design. The bed being shaped like a cone-top of the bed starts of wide and narrows down to a point-will cause different rates of extraction. The top of the bed will start brewing before the bottom of the bed. 

This creates a complex taste profile by mixing this uneven rate of extraction into a homogenous flavor. Some might prefer the complexity and mouthfeel this creates. 

Flat bottom brewers create a flat and level bed which means that coffee particles are extracted at a more even rate to one another. This is done by allowing water to pass through an even and level medium. This gives a more uniform and clear taste profile with a medium to full body. 

Choosing coffee-to-water ratio

Choosing a coffee-to-water ratio is personal preference, to an extent. You can use this variable to adjust the strength of your coffee. This is not interchangeable with over or under-extraction, these are bad qualities. With this, you’re adjusting how many coffee solubles are present to every water molecule (calculated in %TDS). 

Grinding coffee

Using a burr grinder is really important when it comes to consistent extraction. A Burr grinder will shear a coffee bean into more evenly sized particles. Using anything but a burr grinder, will create a significant amount of fines and boulders. With these extremes, you’re ensured a coffee tasting either really underwhelming and hollow or a very dirty cup with extreme bitterness. 

Choosing and heating water (choosing 3rd wave water, lotus and how hot to heat your water)

Water makes up around 98% of the final cup. The properties of the water used in brewing can have a huge effect on the flavor, aroma, body, sweetness and acidity. 

Using hard or soft water can affect the rate and extent of extraction which greatly impacts the flavor of the coffee. 

Water contains mineral contents such as Calcium, Magnesium, Potassium and Sodium. The mineral makeup affects the flavor of the overall cup. For example, hard water will produce bitter or metallic tastes while soft water produces flat or dull tastes. 

pH level in the water used also affects flavor. High pH water (alkaline)  can produces a bitter taste, water with low pH (acidic) can produce a sour taste. 

Generally, the higher the water temperature the higher/faster the extraction. A good rule of thumb is lighter roasted coffee typically needs higher temperature and darker roasted coffee needs lower temperature water. This is attributed to the structural integrity of the cell, in other words, the darker the roast the more soluble your coffee is. 

Choosing filter/brewer

Deciding on a brewer comes down to what you’re looking to get out of your coffee. For example, if you want a complex and vibrant taste, you may want to try a cone brewer like a Hario V60 or a Cafec Flower Dripper. 

If you’re looking for balance and clarity, a flat bottom brewer like the Kalita Wave may be a good choice. 

There are also many variations of these types of brewers that either create faster or slower rates of extraction. This is something to keep in mind if you’re trying to push extraction by grinding finer. This can help you avoid high contact times by having high flow rates and minimal clogging in the filter. 

There are now fast filters as well that can really reduce filter clogging like the Sibarist cone and flat bottom filter. 

Choosing pouring structure (bloom to the rest of brew water)

Pouring structures affect extraction by controlling agitation and coffee slurry temperature. For example, if you let the water completely drain from the bed, then the next pour is going to agitate the surface a lot more compared to having some water still in the bed, the water will act as a cushion for incoming water. Keeping water in the brewer will also maintain temperature by keeping its mass and more hot water being introduced. 

Circular Pours Vs Center Pours (Stay consistent)

Pouring methods like circular pours or center pours will control agitation, another key variable in brewing coffee. Circular pours drop water right on top of the coffee slurry and then proceed to percolate, while center pours create agitation by allowing water to hit the center of the slurry and causes particles to move outwards towards the wall of the brewer. 

You can either stick to one way or create hybrid pours depending on your preference. 

High agitation vs low agitation (Swirling or using melodrip)

Higher agitation can equate to higher extraction. An example to think about is adding hot water to sugar you’re trying to dissolve, the more you mix things, the more you dissolve at a faster rate. 

The melodrip is a great tool to decrease agitation while swirling your slurry will increase agitation. 

Total contact time 

Unless using a full immersion brewer, contact time is indirecting controlled by other factors such as grind size, brewer, to the type of filter and water ratio. . 



Processing and Effects on Brewing

Effects on Brewing

Processing can be thought of as the series of steps involved in transforming harvested coffee cherries into the dried coffee beans that are ready to be roasted. 

Generally, the more processing a coffee goes through, the more soluble it can become. As fermentation breaks down sugars and other organic compounds, it weakens cellular integrity and in turn makes it easier for us to extract soluble compounds. 

We should take this into account when brewing because we want to avoid over-extraction when coffee is in such a deteriorated state. 


Different Processing Methods

Each region of origin may use slightly different terminology, but in general the following definitions are recognized across the industry.

  1. Washed (or Wet) Process: In the washed process, the outer skin of the coffee cherry is removed using a mechanical depulper or by hand. The cherries are then fermented in water tanks to break down the remaining fruit pulp. After fermentation, the coffee beans are thoroughly washed to remove any remaining residue. Finally, the beans are dried either on raised beds or using mechanical dryers until they reach an optimal moisture content.
  2. Natural (or Dry) Process: In the natural process, the whole coffee cherries are dried intact, with the skin and pulp still intact. The cherries are spread out in thin layers on raised beds or patios, where they are dried by the sun. As the cherries dry, they shrivel, and the outer layers of skin and pulp can be easily removed. This process results in coffee beans with a full body, fruity flavor, and a distinct sweetness.
  3. Honey (or Pulped Natural) Process: The honey process is a hybrid between the washed and natural processes. In this method, the outer skin is removed, but a significant amount of the sticky fruit pulp (resembling honey) is left on the beans. The cherries are then dried, either in the sun or using mechanical dryers. The remaining fruit pulp imparts sweetness and fruity flavors to the coffee.
  4. Semi-Washed (or Pulped) Process: In the semi-washed process, the coffee cherries are mechanically depulped to remove the outer skin, but the sticky mucilage layer is left intact on the beans. The cherries are then fermented for a short period to facilitate the removal of the mucilage. After fermentation, the beans are washed to remove any remaining residue and then dried.
  5. Anaerobic/Aerobic Process: The anaerobic process in coffee refers to a specific processing method where coffee cherries are fermented in an oxygen-free or low-oxygen environment. This process deviates from traditional fermentation methods and has gained popularity in specialty coffee production for its potential to create unique and distinct flavor profiles. Here's an overview of the anaerobic process in coffee:
    1. Oxygen-Free Environment: In the anaerobic process, coffee cherries are placed in airtight containers, fermentation tanks, or sealed bags to limit the presence of oxygen during fermentation. This controlled environment helps create different chemical reactions and influences the flavors developed during the process.
    2. Extended Fermentation: The anaerobic process typically involves a longer fermentation period compared to traditional processing methods. Fermentation can range from a few hours to several days, depending on the desired flavor outcome. During this extended fermentation, the coffee cherries undergo various biochemical changes.
    3. Temperature and Pressure Control: The anaerobic process often involves precise control over temperature and pressure. Different combinations of temperature and pressure can influence the fermentation process, resulting in specific flavor characteristics in the final cup of coffee.
    4. Microbial Interaction: Anaerobic fermentation encourages the growth and interaction of specific microorganisms, such as certain strains of yeast and bacteria. These microorganisms interact with the sugars in the coffee cherries, breaking them down and producing unique compounds that contribute to flavor development.
    5. Flavor Profiles: The anaerobic process can yield a wide range of flavor profiles, depending on factors such as the coffee variety, fermentation duration, temperature, and the specific microbial strains present. The resulting coffees often showcase complex and intense flavors, such as fruity, wine-like, or fermented notes, along with enhanced sweetness and acidity.