Making Espresso - Coffee Dosing Tips, Do's and Don'ts

Coffee dosing is the process of determining the precise amount of ground coffee used when preparing espresso. It’s a critical step in achieving the right flavor, balance, and consistency in your espresso shots. Coffee dosing involves both weight and volume, with the former being the more accurate and preferred method in professional settings. Here's a detailed explanation of the principles, science, and tips for coffee dosing when making espresso.

1. The Basics of Coffee Dosing

Weight vs. Volume

• Weight (grams): This is the preferred method for dosing because it allows for precise and repeatable results. When using weight, you measure the mass of ground coffee in grams. This method is more consistent because it accounts for factors like bean density, grind size, and tamp pressure.

• Volume (spoons or scoops): Dosing by volume is less accurate because different coffee beans can have varying densities, and the grind size affects how much fits in a scoop. Measuring by volume often leads to inconsistency in taste and extraction.

2. Scientific Principles Behind Coffee Dosing

Extraction

Coffee extraction refers to the process of dissolving the soluble compounds in coffee grounds with water. When making espresso, the aim is to extract between 18-22% of the coffee's soluble compounds to achieve a well-balanced cup . Under-dosing or over-dosing can cause improper extraction, leading to undesirable flavors.

• Under-dosing (too little coffee) can lead to over-extraction. This occurs when there is too much water relative to the coffee grounds, causing the water to extract more bitter compounds, resulting in a sharp, astringent taste.

• Over-dosing (too much coffee) can cause under-extraction. In this case, water flows too quickly through the puck (the coffee bed in the portafilter), not extracting enough of the coffee's soluble compounds. This can result in a sour or weak espresso.

Grind Size and Dose

Grind size and dose are closely related. A finer grind increases the surface area of the coffee, which means that a lower dose might be needed compared to a coarser grind to achieve the same extraction. Conversely, coarser grounds may require a higher dose to reach optimal extraction times.

Pressure and Dose

The standard for espresso extraction is 9 bars of pressure, but the dose also affects how pressure influences extraction. If the dose is too low, the water will flow through the puck too quickly, leading to under-extraction. If the dose is too high, the puck can become too dense, resulting in water channeling or uneven extraction.

3. Standard Espresso Dosing Ratios

In espresso preparation, the amount of coffee used in relation to the liquid espresso produced is referred to as the brew ratio. A common brew ratio is:

• 1:2 ratio: This means for every gram of ground coffee, you aim to produce two grams of espresso. For example, if you use 18 grams of coffee, you should aim to produce 36 grams of liquid espresso.

Other ratios:

• 1:1 ratio (ristretto): For a more concentrated shot.
• 1:3 ratio (lungo): For a longer shot with more volume.

4. Factors Affecting Coffee Dosing

Bean Type and Roast Level

• Light Roasts: Often require a slightly higher dose because they are less soluble and need more coffee to balance out the acidity and under-extraction risks.

• Dark Roasts: Tend to extract more quickly due to higher solubility, so they may require a slightly lower dose.

Basket Size

Portafilters come with different basket sizes, typically holding between 14 and 22 grams of coffee. The size of the basket determines how much coffee can be dosed properly.

• Single Basket: Typically holds 7-9 grams of coffee.
• Double Basket: Holds 14-18 grams.
• Triple Basket: Can hold up to 22 grams.

Overfilling the basket or using the wrong size can affect the puck’s density, leading to inconsistent extractions.

5. Tips for Coffee Dosing

Do’s

1. Use a Digital Scale: Weigh your dose using a digital scale for precision. This ensures consistency across every shot, which is critical in both home and professional settings.
2. Adjust Dose Based on Grind Size: As you make grind adjustments, you may also need to tweak the dose to maintain proper extraction.
3. Tamp Consistently: After dosing, tamp the coffee evenly with around 30 pounds of pressure to create a uniform puck. Inconsistent tamping leads to channeling, where water finds the path of least resistance and creates under-extracted spots.
4. Dial in with Taste: Start with a standard dose (e.g., 18 grams) and adjust based on taste. If the shot is too bitter or astringent, reduce the dose slightly. If it’s sour or weak, increase the dose.

Don’ts

1. Don’t Overfill or Underfill the Portafilter: Overfilling can cause the puck to contact the brew head, leading to uneven extraction. Underfilling can lead to faster water flow and under-extraction.
2. Don’t Forget to Adjust for Bean Changes: Every time you switch to a new type or roast of coffee, you may need to adjust your dose slightly to account for differences in bean density and solubility.
3. Avoid Eye-Balling: While experienced baristas may be able to dose by feel or sight, this introduces inconsistency. Always measure your dose for repeatable results.

6. Common Mistakes

Overfilling the Basket

If you dose too much coffee into the basket, it may cause the puck to come into direct contact with the brew head, leading to improper water dispersion, channeling, and over-extraction.

Grind Size and Dose Mismatch

An incorrect match between grind size and dose can lead to fast or slow extraction times. If the grind is too coarse for the dose, the water may pass through too quickly, resulting in under-extraction. If the grind is too fine, it may clog the puck and cause over-extraction.

7. Scientific Research on Coffee Extraction

Research published in the Journal of Agricultural and Food Chemistry highlights the role of particle size and brew ratios in coffee extraction . Fine particles increase surface area, which speeds up extraction, but too fine a grind can lead to clogging and uneven extraction. Adjusting the dose, along with grind size, allows for better control over these variables.

Conclusion

Dosing is a key factor in making a consistently good espresso. The right dose ensures proper extraction, flavor balance, and the right mouthfeel. By using a scale, paying attention to grind size, and understanding the interplay of coffee and water, you can fine-tune your espresso shots for optimal results.