The coffee beverage we love so much is the result of infusing ground coffee beans with water for a period of time. There are different methods for extracting the flavor from the coffee grounds.
But what exactly is extraction? Extraction is the transfer of soluble material from a solid (ground coffee) into a liquid medium, usually water. When we brew our coffee, several compounds are extracted, which are responsible for the flavor we enjoy when we drink our coffee brew.
THE TOASTING
To begin with, coffee beans are simply the roasted seeds of the coffee plant fruit. These beans are packed with stored energy: sugars (which give us sweetness and viscosity), fats (viscosity and bitterness), complex acids (which provide sour and/or sweet flavors), caffeine (1% to 4%), and microscopic plant fibers.
When coffee is roasted, the heat first evaporates the moisture trapped inside the beans. As the moisture disappears, the plant fibers become dry, hard, and brittle. If we over-roast, the fibers continue to break down, and the oils rise to the surface and oxidize.
When we add coffee to our roaster, the complex sugars (long-chain carbohydrates) are broken down into simple sugars (short-chain carbohydrates), making them easier to taste. As the roasting process progresses, the sugars caramelize, creating aromas of caramel and nuts; but if we over-roast, the sugars char, resulting in a burnt and smoky flavor.
A significant change also occurs with the acids. When coffee is roasted, the acids break down. If the roast is short, we'll have a high concentration of acids; but as we roast our coffee longer, the acids break down completely, resulting in a mild, burnt flavor.
WHAT ARE THE PHASES OF EXTRACTION?
The first difference we find is the type of bean we're going to brew. Arabica coffees have a higher density, partly due to being grown at higher altitudes, and are therefore less soluble compared to Robusta coffees.
Regardless of the method we use, water will always extract the flavor compounds in this order: fats and acids, sugars, and vegetable fibers.
The first compounds extracted are acids and fats. Acids are the simplest compounds, molecularly speaking, so water dissolves them most easily. These give us the sour flavors. The oils or fats in coffee add body and are not simple in their chemical composition, but they are hydrophobic and separate easily from the ground coffee. In addition, the lighter, floral, and fruity aromatic compounds are extracted in this first phase.
Sugars are extracted next. Even simple sugars are more complex than acids. Therefore, water needs more time and/or energy to dissolve them completely.
Finally, the water will begin to break down the plant fibers, which, like all plant matter, have a dry and bitter taste.
When tasting brewed coffee, we often describe it as under-extracted or over-extracted. Under-extracted coffees have a sour or sharp taste. This is because the water hasn't had enough time to break down sufficient sugars to balance the acids from the first part of the extraction. Over-extracted coffees have a bitter, light, almost hollow taste. This is because the water has extracted all the available sugars and has begun to break down the plant fibers that make up the coffee.
Optimal extraction
Optimal extraction is the desired extraction. Here we can perceive a balance between the basic flavors that coffee provides: acidity, sweetness, and bitterness.
A sip of espresso isn't defined solely by the quality of its extraction; the concentration of the beverage is equally important. When we say concentration, we're not referring to caffeine content. In coffee, concentration relates to the amount of dissolved compounds in the beverage. Filter coffee has approximately 1-2% dissolved coffee compounds; the other 98-99% is water. Espresso is a much more concentrated beverage: it's made up of 7-12% dissolved compounds and 88-93% water.
Once you've defined your target flavor, it's time to adjust the grind for ideal extraction. If your drinks taste too sour, you'll want to extract more from the coffee. The easiest way to do this is to use a finer grind and ensure your tamping is even and doesn't cause channeling. This will have two effects:
• Smaller particles will slow the flow of water through the coffee, giving it more time to extract the sweetness;
• Smaller particles will have more exposed surface area, which will facilitate the entry of water into the coffee.
If your drinks taste very weak and bitter, you'll want to extract less from your coffee. Again, the easiest way is to adjust the grind; this time, make it coarser.
The best-selling specialty coffees
View all cafes
