Exploring the Factors Behind the Rise of Coffee Grounds in Pour-over Brewing

Pour-over brewing is a popular method for extracting the rich flavors and aromas from coffee grounds. But if you’ve ever noticed that some grounds float while others sink during the brewing process, you may have wondered why. In this article, we will unravel the mystery of grounds buoyancy in pour-over brewing. By exploring the various factors that influence their behavior, we aim to shed light on this fascinating aspect of the brewing process and deepen our understanding of the science behind the perfect cup of coffee.

Particle size and density

The size and density of coffee grounds play a crucial role in determining whether they float or sink during pour-over brewing. Finely ground coffee tends to be denser and more likely to sink, while coarser grounds are often lighter and can float. In addition, variations in bean origin, roast level, and grind consistency can affect the density of the grounds. For example, lighter roasted beans generally have a lower density, which can contribute to increased buoyancy.

Degassing and freshness

Freshly roasted coffee beans release carbon dioxide gas during the roasting process and continue to degas over time. This trapped gas can create air pockets in the grounds, making them more buoyant. Therefore, fresher beans are more likely to produce grounds that float. Conversely, as coffee ages, the degassing process slows down, reducing the likelihood of buoyant grounds. However, it’s important to note that degassing alone is not the sole factor; other variables, such as particle size and density, still play a significant role in determining buoyancy.

Bloom and extraction

During the initial phase of pour-over brewing, known as bloom, water saturates the coffee grounds, causing them to release carbon dioxide. This process creates a foamy layer on top of the brew, and the release of gas can contribute to the buoyancy of the grounds. As the brewing process progresses and the coffee is extracted, the grounds may lose buoyancy and begin to sink. The rate at which extraction occurs, as well as the specific brewing technique and water temperature, can affect the buoyancy of the grounds throughout the brewing process.

Variability between coffees

It’s important to recognize that the behavior of coffee grounds can vary among different coffee beans and origins. Factors such as bean density, moisture content, and roast level can vary significantly, resulting in variations in buoyancy. For example, certain coffees with denser beans or unique processing methods may have different buoyancy characteristics. Exploring different coffees and experimenting with different brewing techniques can provide valuable insight into the specific behavior of different coffee grounds.

Common brewing techniques that can affect grounds buoyancy

Several common brewing techniques can affect the buoyancy of coffee grounds during the brewing process. Here are a few examples:

  1. Immersion brewing: In immersion brewing methods, such as French press or Aeropress, the coffee grounds are completely submerged in water for a period of time. During immersion brewing, the carbon dioxide gas trapped in the grounds is released, which can contribute to increased buoyancy. However, as extraction progresses and the grounds become saturated with water, they may gradually lose their buoyancy and begin to sink.
  2. Pour-over brewing: Pour-over brewing methods, such as V60 or Chemex, involve the controlled pouring of water over the coffee grounds. The initial stage of pour-over brewing, known as blooming, where hot water is poured over the grounds in a circular motion, causes the release of carbon dioxide gas. This gas release can create a foamy layer on top of the brew, resulting in floating grounds. However, as brewing continues and extraction intensifies, the grounds may lose their buoyancy and eventually sink.
  3. Espresso brewing: Espresso brewing involves forcing pressurized water through finely ground coffee at high temperatures. The compacted nature of espresso grounds, combined with the high pressure and temperature, often results in a denser coffee puck. As a result, espresso grounds are more likely to sink due to their higher density than coarser grounds used in other brewing methods.
  4. Cold brewing: Cold brewing involves soaking coffee grounds in cold or room temperature water for an extended period of time, typically 12 to 24 hours. The slow extraction process of cold brewing allows for increased release of carbon dioxide from the grounds. As a result, the grounds may initially become more buoyant. However, as the extraction progresses and the coffee brews longer, the grounds may gradually lose their buoyancy and sink.

It’s important to note that the specific variables within each brewing technique, such as grind size, water temperature, and extraction time, can also affect the buoyancy of coffee grounds. Experimenting with different brewing techniques and parameters can help you observe and understand the effects on the behavior of the grounds, allowing you to achieve the desired results in your cup of coffee.

Examples of coffees with distinct buoyancy characteristics

Coffee beans can indeed exhibit different buoyancy characteristics due to variations in bean density, moisture content, and processing methods. Here are a few examples of coffees known for their unique buoyancy characteristics:

  • Ethiopian Yirgacheffe: Ethiopian coffees, particularly those from the Yirgacheffe region, are known for their vibrant flavors and distinctive buoyancy. The beans are often densely packed and have a high moisture content, which can contribute to increased buoyancy during brewing. You may see these grounds float during the early stages of brewing and gradually lose their buoyancy as extraction progresses.
  • Colombian Supremo: Colombian Supremo is a popular coffee known for its medium to low density. The beans are relatively large and tend to have a moderate moisture content. As a result, the beans can exhibit balanced buoyancy, neither sinking too quickly nor staying afloat for long periods of time. This balanced behavior allows for even extraction and optimal flavor development.
  • Indonesian Sumatra Mandheling: Coffees from the Sumatra region, such as Sumatra Mandheling, often have unique characteristics due to their processing method. The wet hulling process, known as “Giling Basah”, results in coffee beans with a higher moisture content and a distinct earthy flavor profile. These beans can exhibit a slightly higher buoyancy during brewing, with the grounds initially floating and gradually sinking as the extraction progresses.
  • Kenyan AA: Kenyan AA coffees are known for their bright acidity, intense flavor and high bean density. The beans are typically large and dense, which can result in grounds that sink relatively quickly during brewing. These dense grounds require careful brewing techniques to ensure adequate extraction and flavor balance.

It’s important to remember that there can be variation within coffee varieties due to factors such as processing methods, roast level, and specific growing conditions. Therefore, lift may not be consistent across all beans of a particular variety. Exploring different coffee varieties and observing their buoyancy characteristics can be an exciting aspect of the coffee brewing journey, allowing you to appreciate the unique qualities each variety brings to the cup.


The floating and sinking of coffee grounds during pour-over brewing can be attributed to a combination of factors, including particle size, density, degassing, freshness, and the extraction process. Understanding these variables helps demystify the behavior of coffee grounds and allows coffee enthusiasts to fine-tune their brewing methods for optimal results. Ultimately, by appreciating the science behind coffee grounds buoyancy, we can further enhance our coffee brewing skills and unlock the full potential of that perfect, flavorful cup of pour-over coffee.


Why do some grounds float and others sink when brewing by pour over?

One thing to keep in mind is that coffee beans contain CO2. This causes grounds to float and foam. If the beans don’t have any CO2 they won’t float. This is also a sign that they have gone stale.

Why do some coffee grounds float?

Coffee grounds, buoyed by gases formed in roasting, float when hot water is added, while tea leaves immediately get wet and sink. When you’re making coffee, you have to find some way of getting the water into the grounds so that you can brew the flavor, but before the bitter tannin starts to be extracted.

Should coffee grounds sink?

Unlike most foods, coffee grounds clump together in water rather than breaking down. With time, the grounds can build up inside your sink drains, creating clogs that can prohibit the drains from doing their job. Coffee grounds should always go in the garbage can or compost.

How ground should coffee be for Pour over?

For pour over coffee, the best grind to use is a medium-coarse grind. A medium-coarse grind will be similar in size to a French press grind but less chunky and will feel slightly smoother. If you are using a cone-shaped pour over, then use a medium-fine coffee grind instead.

Why do coffee beans sink?

Unfortunately, coffee grounds do not break down in water, so instead of grinding up and washing away as normal foods do in a garbage disposal, they clump together and as time goes by, the grounds can form a clump and pack the drain until it develops a clog.

Does real coffee float or sink?

Roast A will always float when pouring hot water over, throughout the entire brewing process. Roast B will always sink, especially towards the end of brewing.

Does cold water make coffee grounds sink?

Don’t Add Cold Water

Grounds sink when they cool. Adding cold water makes cold coffee. I never add water. The grounds usually sink in 5 minutes, quicker if the air is cold.

Why are coffee grounds bad for disposal?

Both coffee grounds and eggshells are sedimentary in nature, if too much is placed in at one time, or if the plumbing is restricted, it can create a clog or a ‘slow drain’ situation.

Can I dump coffee grounds down the toilet?

No. Coffee grounds clump together in water instead of breaking down, which is a great recipe for drain clogs. While it’s okay to put a minute amount down your sink (especially if you flush it with plenty of water), it’s not something you should do on a regular basis.