Why your espresso shot times change as coffee beans age: a barista’s guide

There is nothing more satisfying for a home barista than pulling the perfect espresso shot. You have meticulously dialed in your grinder, perfected your puck preparation, and achieved that beautiful, syrupy extraction in your target time. For a few days, everything is perfect. Then, seemingly overnight, your shots start gushing out, finishing seconds too early and tasting thin and sour. You have not changed a single thing, so what went wrong? The culprit is often hiding in plain sight: your coffee beans are aging. Coffee is a fresh, agricultural product, and its characteristics change daily. This article will delve into the science of why coffee beans evolve after their roast date and how that directly impacts your espresso extraction times, turning you into a more intuitive and consistent barista.

The critical role of CO2 degassing

The most significant factor influencing your shot times as beans age is a process called degassing. During the roasting process, a multitude of complex chemical reactions occur inside the coffee bean. One of the major byproducts of these reactions is carbon dioxide (CO2). A large amount of this gas becomes trapped within the bean’s cellular structure.

When you grind freshly roasted coffee and pull a shot, this trapped CO2 plays a crucial role. As the hot, pressurized water from your machine hits the coffee puck, the CO2 is released and actively works against the flow of water. Think of it as a form of “gaseous resistance.” This gas creates pressure that pushes back against the water, slowing down the extraction and resulting in a longer shot time. This is why coffee that is too fresh can be difficult to work with, often leading to channeling or overly slow shots.

However, this CO2 does not stay locked in the bean forever. From the moment the roast is finished, the beans begin to slowly release this gas. The rate of degassing is highest in the first few days and gradually tapers off. As your beans age and lose CO2, there is less gas to resist the water. Consequently, the water flows through the coffee puck more easily and quickly. This is the primary reason why a grinder setting that produced a 30-second shot three days after roast might produce a 20-second shot ten days after roast.

Changes in bean structure and solubility

Beyond degassing, the physical structure of the coffee bean also changes over time. As beans age, they lose moisture and their internal structure becomes more brittle and porous. This has a direct impact on how they shatter when they go through your grinder.

A more brittle bean can fracture differently than a fresher, more pliable one. Even at the same grinder setting, an older bean might produce a slightly different distribution of particle sizes. This change, combined with the lack of CO2, means your once-perfect grind setting is no longer creating the ideal density and resistance in the puck. The water finds it easier to create channels and pass through quickly, leading to an under-extracted and unbalanced shot.

Furthermore, the solubility of the coffee’s flavor compounds changes. The volatile aromatic oils that contribute to the wonderful flavors and aromas in your cup begin to degrade and oxidize when exposed to air. Older beans become less soluble, meaning it is harder to extract the sweet, desirable flavors from them. When a shot runs too fast on aging beans, you get a double negative: not enough contact time for proper extraction, and less soluble compounds to extract in the first place. This results in a cup that is not just fast, but also tastes noticeably stale, flat, or papery.

How to adjust your grind for consistency

Understanding the “why” is the first step; the next is knowing how to react. Since aging beans offer less resistance to water, your job as a barista is to re-introduce that resistance to maintain a consistent extraction time and quality. The most effective tool you have for this is your grinder.

To counteract the effects of degassing and aging, you will need to grind your coffee finer. Here is a simple, effective workflow to follow:

• Establish a baseline: When you open a new bag of coffee, dial it in to your preferred recipe (e.g., 18g of coffee in, 36g of espresso out, in 28-32 seconds). Note the grinder setting.
• Monitor your shots daily: Pull your first shot of the day and pay close attention to the time. Has it started to speed up?
• Make small adjustments: If your shot time has decreased by more than a couple of seconds, adjust your grinder one small step or “notch” finer. It is crucial to make small, incremental changes.
• Purge your grinder: After adjusting the setting, grind a small amount of coffee (a few grams) and discard it. This ensures that the grounds in your portafilter are at the new, finer setting and not a mix of old and new.
• Pull and evaluate: Pull another shot and check the time. Repeat the process if necessary until you are back within your target range.

This process of making micro-adjustments to your grind every day or two will help you achieve delicious, consistent espresso from the first day you open a bag to the last.

Dialing in over time: a practical example

To make this concept more concrete, let’s look at how a bag of coffee might change over two weeks and the adjustments required. Imagine you are aiming for a shot time of 30 seconds with an 18g dose and 36g yield. The “Grinder Setting” is just a hypothetical number to illustrate the change.

This table demonstrates the typical progression. You do not make massive changes, but rather small, responsive adjustments as the coffee ages. By being observant, you can stay ahead of the changes and keep your espresso tasting great.

Mastering espresso is not about finding one “magic” setting that works forever. It is about understanding that coffee is a dynamic ingredient that is constantly evolving. The primary reason your shot times speed up is the natural process of CO2 degassing, which reduces the puck’s resistance to water. This effect is compounded by changes in the bean’s physical structure, making it more brittle and altering its solubility. The key to consistency, therefore, is not to resist this change but to adapt to it. By making small, daily adjustments to your grinder—specifically, by grinding finer as the days go by—you can compensate for these natural processes. Embracing this workflow will elevate your skills and empower you to pull delicious, balanced shots from every single bag of coffee you buy.