What Causes Thin Espresso Crema? Why Does Crema Have Many Large Bubbles? Factors That Make Espresso Taste Bad?

Understanding Thin Espresso Crema and Large Bubbles

Recently, FrontStreet Coffee noticed that many baristas encounter this issue when extracting espresso: "The extracted espresso has thin crema with many obvious large bubbles! The entire coffee tastes bland with a thin mouthfeel, and the presence of bubbles affects the beauty of latte art patterns!" These baristas then post online seeking help. So what exactly causes this situation to occur?

Main Influencing Factor: Incorrect Grind Size

Many factors can lead to this situation, but regardless of the cause, they all relate to "grind size," and grinding too coarse is the primary reason for this problem.

When coffee grounds are too coarse, the gaps between particles increase, giving hot water more space to flow. During extraction, this increases the flow rate of hot water, which can quickly penetrate the coffee bed, allowing us to extract the target liquid weight faster. However, as flow rate increases, the contact time between water and coffee decreases. This not only prevents hot water from fully extracting flavor compounds from the coffee but also creates strong impact force as the rapidly flowing coffee liquid drips down. This forceful coffee liquid then pushes air into the espresso, forming visible large bubbles.

Although these bubbles disappear quickly, the coffee's flavor doesn't improve as a result. Therefore, when this situation occurs, we need to adjust the "culprit" – the grind size. As mentioned earlier, this is caused by grinding too coarse! So we need to adjust the grinder to a finer setting. Specific adjustments can follow the formula FrontStreet Coffee has shared before – we can adjust the grind according to this formula.

For example, using the formula of 20g coffee grounds with a 1:2 ratio (extracting 40ml of espresso liquid) over 30 seconds. If we use 20g of coffee and extract 40ml in 20 seconds, we need to move the grinder several clicks toward the finer setting. FrontStreet Coffee uses the Galileo Q18 grinder, where each adjustment click increases or decreases extraction time by about 3 seconds. So when we extract 40ml in 20 seconds, we need to move 3 clicks finer. When the time is very close to the target, we can make fine adjustments based on taste, and then we'll have a rich crema and delicious espresso! Generally, besides changing to a new grinder which might cause this extremely coarse grinding situation, there are two other factors that can cause significant changes in grind size.

1. Improper Storage of Coffee Beans

When we finish our coffee time for the day and no longer need to extract espresso, we should seal the coffee beans to reduce the loss of flavor compounds. However, if we don't seal them properly, leaving gaps that allow the beans to "breathe," the beans will continuously contact fresh air in the following time, significantly losing carbon dioxide and aromatic compounds.

In just a few short hours, carbon dioxide and flavor compounds can completely disappear. When we extract the next day, the coffee will no longer work with the original grind size due to the loss of carbon dioxide and flavor compounds. The extracted espresso will not only have thin crema but also bland flavor. Even if we readjust to a suitable grind size, the flavor and crema can hardly return to their peak state. Therefore, we must pay attention to proper storage during long periods without extraction to extend the flavor period of coffee beans.

2. Switching to Beans with Different Roast Levels

As we all know, the characteristic of dark roast coffee beans is "easy to extract"! During long roasting, the beans have low density and high brittleness, allowing hot water to easily extract all their internal compounds. This characteristic means they don't need too fine a grind (compared to extracting light roast espresso) to allow water and grounds sufficient extraction time. After all, with their "sensitive skin" (dark roast beans), they release large amounts of carbon dioxide upon contact with hot water. Carbon dioxide is not only the main component of Crema but also fills gaps, slowing the flow rate of hot water. Therefore, during extraction, the presence of large amounts of carbon dioxide allows water more extraction space.

When we suddenly replace the dark roast beans in the hopper with lighter roasted beans, because they don't have the "advantages" of dark roast beans and are difficult to extract (due to higher density and lower brittleness), and their carbon dioxide content is not as abundant to slow the flow rate of hot water, we need to adjust to a finer grind to increase the surface area in contact with hot water, allowing better extraction of flavor compounds. But if we don't adjust the grind after changing beans, the ground coffee will be too coarse, causing splattering during extraction, resulting in thin-flavored coffee with sparse crema.

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473