The grind size is one of the most important factors for successful coffee brewing. Incorrect settings lead to watery or bitter taste and can make even high-quality coffee undrinkable. The grind size determines how quickly and intensely the water extracts the aromatic compounds from the coffee grounds – a process known as extraction.
The choice of grind size primarily depends on your brewing method. Generally, the finer the grind size, the shorter the contact time with the water. Here you will learn how to find the perfect grind size for each brewing method.
Why grind size is so important
The keyword is: surface area. The coffee grounds come into contact with water in every brewing method. The surface area of the grounds determines the strength of the extraction.
Fine coffee grounds have more surface area – the water takes longer to find a path through the grounds. The finer the grind size, the more intense the extraction. To prevent over-extraction, a shorter extraction time must be observed with fine coffee grounds.
The higher the pressure, the finer the grounds can be. That's why espresso grounds are always very fine – they are pressed through the portafilter at 9 bar.
What is coffee extraction?
Coffee extraction is the process by which hot water dissolves soluble compounds from ground coffee. These substances – such as acids, oils, sugars, and caffeine – contribute to the characteristic aroma and taste of the coffee.
A maximum of 30% of the ingredients in a ground coffee bean can be extracted – but 30% is not the goal, as the coffee then tastes bitter and too strong. The Specialty Coffee Association of Europe (SCAE) recommends an optimal extraction of approximately 18–22% to achieve a balanced aroma and aromatic taste.
• Below 18%: Under-extraction (watery, sour)
• 18–22%: Optimal (balanced, aromatic)
• Above 22%: Over-extraction (bitter, too intense)
Grind size for each brewing method
| Brewing method | Grind size | Contact time |
|---|---|---|
| Portafilter / Espresso Machine | Very fine (like flour) | 25–30 seconds |
| Automatic Coffee Machine | Fine | 20–30 seconds |
| Moka Pot (Bialetti) | Fine to medium | 3–4 minutes |
| Filter Coffee / Pour-over | Medium (like table salt) | 2.5–4 minutes |
| AeroPress | Medium to coarse | 1–2 minutes |
| Chemex | Medium to coarse | 3.5–4.5 minutes |
| Siphon | Medium to coarse | Max. 2 minutes |
| French Press | Coarse (like semolina) | 4 minutes |
| Karlsbad / Bayreuth Pot | Very coarse | 4–6 minutes |
| Cold Brew | Coarse | 12–24 hours |
Avoiding over-extraction
Over-extraction occurs when too many bitter substances and tannins are dissolved from the coffee. The coffee then tastes unpleasantly bitter, too intense, and the subtle nuances are overshadowed. Technically, over-extraction occurs when more than 22% of the ingredients have been extracted.
• Taste: Very bitter, unpleasantly intense, astringent
• Color: Very dark, almost black
• Crema (for espresso): Extremely dark, almost black
• Mouthfeel: Dry, furry
- Choose a coarser grind size
- Lower the water temperature (ideal: 89–95 °C)
- Shorten the extraction time
- Use less coffee
- For portafilters: Do not tamp too hard
Avoiding under-extraction
Under-extraction occurs when too few aromatic compounds have been dissolved from the coffee. The coffee then tastes watery, flat, sour, and underdeveloped. Technically, under-extraction occurs when less than 18% of the ingredients have been extracted.
• Taste: Watery, sour, flat, lacking body
• Color: Very light, pale
• Crema (for espresso): Light, thin, white or completely absent
• Mouthfeel: Thin, without substance
- Choose a finer grind size
- Increase the water temperature (ideal: 92–95 °C)
- Extend the extraction time
- Use more coffee
- For portafilters: Preheat the portafilter and machine
What influences the grind size?
In addition to the brewing method, other factors influence the optimal grind size:
- Coffee variety: Some varieties are better suited for espresso, others for filter
- Roast level: Dark roasts (espresso) are ground finer, light roasts (filter) coarser
- Extraction duration: Shorter contact time = finer grind size
- Pressure: Higher pressure (portafilter) = finer grind size
- Water temperature: Higher temperature = more intense extraction
- Personal taste: Experiment until you find your ideal setting
The grind size cannot turn a fruity-floral coffee into an almond-spicy one. The basic characteristics are determined by the bean, origin, and roast.
The right coffee grinder
A good coffee grinder is crucial for consistent grounds. There are two main types:
- Hand grinders: Inexpensive, quiet, good for travel – require some effort
- Electric grinders: Fast, convenient, precisely adjustable – higher initial cost
- Burrs or conical burr grinder (NOT blade grinder!)
- Precise adjustment options for grind size
- Consistent texture of the grounds
- For portafilters: Grinder must be able to grind fine enough
Special tips for portafilters
Portafilter brewing requires special attention to grind size:
- Extraction time: Ideally 25–30 seconds for a double shot
- Coffee quantity: Keep 18.5–21 g consistent for a double shot
- Tamping: Once with 15–20 kg of pressure
- Temperature: 89–95 °C for optimal aroma extraction
Avoid small channels in the grounds through which the water flows. This occurs due to uneven distribution or tapping after tamping. Result: Uneven extraction and poor taste.
Conclusion: The perfect grind size
The grind size is a crucial factor for excellent coffee, but not the only one. Perfect coffee brewing is the interplay of:
- Grind size: Adapted to the brewing method
- Coffee quantity: Correct dosage (Brew Ratio)
- Water quantity: Balanced ratio
- Water temperature: 89–95 °C depending on the method
- Extraction time: Adapted to grind size and method
The shorter the contact time with water, the finer the grind size should be. Over-extraction leads to bitterness, under-extraction to a weak flavor. Experiment with the settings until you find your perfect coffee!