How to Solve Espresso Perforation Phenomenon? What Causes Inconsistent Espresso Flow? Why Does Espresso Machine Extraction Time Fluctuate?

Hidden Factors Affecting Espresso Extraction and Their Solutions

As we all know, the most important task for baristas every morning when they arrive at the shop is calibrating the taste of espresso. After sitting overnight, the condition of coffee beans has already changed due to their natural degassing characteristics, which will alter the extraction time of espresso and potentially affect the taste. Therefore, to ensure that today's coffee maintains the same delicious flavor, baristas calibrate the espresso taste when they start work in the morning.

However, besides being influenced by the inherent characteristics of coffee beans, many other hidden factors can affect coffee extraction. This is why we can observe changes in espresso flow/extraction speed not just after a long interval like overnight, but even every few hours or tens of minutes. The flow might be too fast or too slow. Relatively speaking, these factors have less impact on taste, but it's still important to understand them, as this can help us make better adjustments and avoid unnecessary effort. Next, FrontStreet Coffee will share what other hidden factors affect espresso extraction and their respective solutions.

1. Residual Coffee Powder in Grinder

Whether it's a timed grinder or a dosing grinder, after grinding coffee beans each time, some coffee powder will remain in the grinder's internal channels due to static electricity or the grinder's structural design. FrontStreet Coffee has specifically measured this before - the residual amount is approximately 1-4g.

When coffee beans are ground into powder, the rate of gas release increases exponentially due to the destruction of the complete structure and the increase in total surface area. If we don't use this portion of coffee powder within a short time after grinding, then over time, the carbon dioxide and aromatic substances in the powder remaining in the channels will completely dissipate. When this powder is used after complete gas dissipation, not only will it reduce the overall extracted aromatic substances, but the loss of carbon dioxide will also affect extraction speed, causing deviations in the overall extraction.

Therefore, when the interval between grinding coffee powder is too long, it's best to first remove this "old" coffee powder remaining in the channels, then use the "new" coffee powder from subsequent grinding to make coffee. This way, the residual powder won't affect the coffee's extraction and taste.

2. Coffee Machine Water Temperature

Similar to the grinder principle, when the extraction interval of the coffee machine is too long, it may also develop some minor issues that affect extraction. For example, the temperature of the hot water.

In the article two days ago, FrontStreet Coffee shared that the temperature of hot water directly affects the efficiency of coffee extraction. This efficiency refers not only to the dissolution rate of flavor compounds but also to the release rate of carbon dioxide. When water temperature is higher, more carbon dioxide is released in the same amount of time; when water temperature is lower, less carbon dioxide is released in the same amount of time. The amount of carbon dioxide affects the pressure build-up speed in the coffee machine, so the quantity of carbon dioxide released will also affect espresso extraction. When the coffee machine's extraction interval is too long, the temperature of the hot water in the pipes will change, thereby affecting coffee extraction. Therefore, FrontStreet Coffee strongly recommends that everyone run a blank flush of hot water before each espresso extraction. This not only ensures more stable extraction but also cleans away the "coffee residue" attached to the brew head.

3. Coffee Machine Pressure

In addition to water temperature, the coffee machine's pressure can also deviate due to excessively long extraction intervals. As one of the important extraction parameters for espresso, pressure fluctuations will similarly affect the coffee's flow state. When we haven't extracted espresso for more than 30 minutes, we can clearly notice that the flow rate of the first extracted espresso will be significantly different from before. Even if you use "fresh powder" and release hot water before extraction, the flow rate still changes considerably. This is caused by the water pump being "just awakened" and still in a dazed state.

Generally, the second espresso extraction will return to normal, but many friends often use the extraction time and taste of the first espresso as a standard and make adjustments accordingly. After trying several versions, they discover that the coffee extracted with the original parameters tastes best (Design: I'm familiar with this routine). In situations like this, we can use a blind basket to "wake up" the coffee machine's pump in advance, then proceed with espresso extraction. This can reduce the error introduced by the first extraction, allowing us to better determine whether taste and parameters need adjustment.

4. Environmental Changes

In FrontStreet Coffee's tweets, there's a topic with a very high repetition rate: Why is espresso always hard to adjust on rainy days? It mentions that the stability of espresso extraction is affected by environmental factors such as temperature, humidity, air pressure, etc. Since there are detailed explanations in the blue text links, FrontStreet Coffee will briefly summarize here.

Let's take environmental humidity as an example! When environmental humidity is high, ground coffee powder will have more "stickiness" and will more easily clump together. If clumped coffee powder is directly tamped into the portafilter without being broken up, the coffee puck will be more prone to "channeling" due to the presence of clumped powder, greatly increasing the chance of uneven extraction. Next is air pressure! Air pressure is usually lower on rainy days, and coffee machines need pressure to assist when extracting espresso. Pressure is generated by the coffee machine's pressure pump, which creates a pressure difference relative to atmospheric pressure. But because atmospheric pressure is relatively lower on rainy days, the reduction in external pressure will cause the actual extraction pressure generated by the pump to decrease. This makes it more difficult for us to stably extract delicious espresso.

There are many similar effects, not necessarily limited to high humidity environments and rainy days. Since it's difficult for us to control the impacts brought by environmental changes, we can only make timely corrections when coffee extraction problems occur (or treat the symptoms according to the methods in the links). Generally, FrontStreet Coffee recommends calibrating espresso taste every four hours to ensure consistent quality.

5. Grinder Hopper Pressure

For shop production, maintaining the hopper pressure of the grinder is a very important matter. Friends who frequently read FrontStreet Coffee's articles know that hopper pressure's impact on extraction cannot be underestimated. So-called hopper pressure refers to the downward pressure formed by the accumulation of coffee beans in the bean hopper.

When coffee beans are being ground, the presence of certain hopper pressure will improve the grinding quality of the coffee beans, and the ground particles will be more uniform as a result. If coffee beans are not pressed down by weight during grinding, they will easily bounce around due to being squeezed! This will greatly reduce the uniformity of the grinding, thereby decreasing quality. If a shop wants to maintain stable production, it's best to keep the capacity in the bean hopper above half full. Alternatively, you can use other heavy objects (such as books) to press down on the coffee beans after sealing them in dust-proof packaging.

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