Pressure Profile Theory and Espresso

Extraction and Flavor

Brewing coffee is a huge part of our everyday lives. To most, the process of brewing coffee seems simple and often mundane. In reality, this couldn't be further from the truth. From the moment brewing begins, a complex series of chemical reactions takes place to draw the flavor out of the beans and into the coffee. We refer to this process as extraction.

The focus of this article is not on the extraction process itself. Rather, we will cover the single variable of pressure profile theory. This will hopefully lay the groundwork for discussion of pressure and how it relates to extraction flavor.

For a more in depth discussion of extraction theory and how it relates to flavor, please check out the amazing work done by Matt Perger and the crew at Barista Hustle.

For now, our focus will be on the single variable of pressure, and how it relates to flavor in our espresso. An over-simplified explanation of extraction and flavor is this: both over and under extraction will yield negative flavor attributes. The further away from our target, the more severe the flavor fault will be. While there are many more factors in play, this generality will work well enough for the discussion at hand.

Pressure Profile Theory

So what is pressure profile theory? To be honest, it is the only thing we could think of to call our thoughts and ideas about what we were experiencing with the Strada EP. We had some ideas of how coffee flavor might be affected, but without actually exploring the topic hands on these were just logical guesses. When we received the Strada EP in the summer of 2018, we immediately began testing these ideas, and recording our subjective results.

In light of these observations, we began to formulate our thoughts into what we hope will become a pattern of predictable cause and effect results. Going forward we will refer to these observations as pressure profile theory. Theory is a great word for these findings, because there is so little information available about espresso and pressure profiling. With enough baristas testing these theories and adding to the conversation, perhaps we can draw more confident conclusions, and turn this theory into law.

Pressure and Extraction

At the most basic level, pressure and extraction are intimately related. They are a direct relationship, meaning that as we increase pressure we increase extraction. This has been a topic of discussion to some degree in the past few years. Many shops have begun to experiment with adjusting their set espresso pressure lower than the standard 9 Bar. Many have found that lower pressure has resulted in more flavorful espresso, or higher extraction coffee with less of the negative flavor components.

While pressure and extraction are a direct relationship, they are not a proportional relationship. There are limits to the extraction process, and at some point increasing pressure will begin to have a decreasing effect on extraction. Within this extraction range, we have almost limitless potential to find different coffee attributes. Knowledge of this extraction spectrum can aid in finding the optimal espresso flavor. (For more on extraction ranges, check out this article by Scott Rao)

Tannins, and the Bitter Truth

One of the components of extraction are tannins. These chemical compounds are present in lots of foods, and they add to the perception of bitterness and astringency. These traits are desirable at times, such as in some wine and various foods. Astringency in the right proportion can make a coffee taste crisp or clean, desirable traits for some offerings. When not in balance with the brewed coffee, tannins can make the coffee taste bitter and mouth-drying astringent. Not necessarily great traits in your morning cup.

Life is all about balance, and your coffee's chemical composition is no different. While tannins aren't necessarily overly desirable, they are present in all extraction processes. The trick to finding this balance is understanding where the majorityof these flavor compounds are coming from. Drawing up general conclusions can then help guide us in designing pressure profile theory.

Generally speaking, the perception of tannins begins to become more prominent towards the end of the extraction process. Whether this is due to actual tannin extraction increasing towards the end of the brew process won't be covered here, but the fact that they are more pronounced is pretty widely accepted in the coffee community. Understanding this basic concept lays the foundation for the next step in pressure profile theory.

Surfing the Sweetness Curve

What if there was a way to prolong extraction, while avoiding all of the negative attributes of tannins? This question kept us up at night. For real, we drank so much espresso testing this theory that we couldn't sleep. The results were worth the heart palpitations, however. What we discovered is now in use in our espresso program, and the results are tasty.

While designing different profiles, one trend began to stand out. Most of our espresso offerings benefited from the same shape of profile, time and time again. Although all of the coffees required different pressures at different times, the shape of the curves all had one common trait. This began to form the first principle in our pressure profile theory.

Time and time again, we ended up with a fast ramp up to peak pressure, followed by a pressure drop until the brew process was complete. This curve seems to allow for a longer extraction, without the associated tannin-bomb tailings. It is our finding that each coffee has it's "sweet spot." This sweet spot is both literal and figurative. Extracting longer, while decreasing pressure throughout the brew process tended to allow us to draw out more sweetness without the added perception of bitterness.

In pressure profile theory, we now refer to this curve as the Sweetness Curve. The general understanding is that by lowering the pressure throughout the shot, we are able to continue drawing out the "good stuff" and stay below the pressure where the tannins begin to overwhelm the cup. This Sweetness Curve seems to have an inverse relationship with extraction. The further we push extraction, the lower the Sweetness Curve drops. If we are able to follow this curve down, the perception of tannins can be avoided to a very large degree.

The Tannin Zone

On the other side of this Sweetness Curve is what we can call the Tannin Zone. This is best described as the range of extraction where the sweetness is overtaken by the tannins, and the coffee quality begins to decrease. While this may not be the experience for everyone, we find that crossing into the Tannin Zone results in a sudden and drastic increase in tannins. This seems to be a sharp threshold. Pushing right up against this line will result in a sweet and pleasant cup, crossing into the Tannin Zone by even a small amount seems to result in a sharp over-extracted flavor experience. This Sweetness Curve is best understood by trying to stay close to, but being careful not to cross over into the Tannin Zone.

Acidity and the Pressure Pump

So what is next? In the next article we will be covering the acidity spectrum, and our findings on how to get that acidity to really pop. The acidity spectrum was our next discovery, and it quickly formed the second principle of our pressure profile theory. The acidity variables are such a large factor that they require a dedicated article just to scratch the surface.

This series of articles are based on our findings on the Strada EP, and pressure profile theory that we are developing in real time. As these theories are debated, tested and pushed to their limits, we fully expect to adapt our understanding along with those results.

Constructive dialogue is appreciated, and encouraged. Do you work on a pressure profiling machine? Please share your thoughts and comments so we can all learn. Let's push the limits together.