Rethinking Paper Rinsing:
Rethinking Paper Rinsing
Paper rinsing refers to the process of running hot water through a paper filter before brewing coffee. It is generally done for purposes such as "removing the paper smell" or "warming up the equipment."
However, paper rinsing is not an essential step, so whether or not to do it is decided based on the objective.
At THE WORD COFFEE, we intentionally do not perform paper rinsing.
The reason is that, as a result of repeated testing, we believe that the current method without rinsing allows us to express the ideal coffee that THE WORD COFFEE aims for.
First, as a premise, at THE WORD COFFEE:
• We use oxygen-bleached paper with almost no odor (THE WORD COFFEE uses CAFEC Abaca coffee paper filters).
• We use a resin V60 dripper with low thermal conductivity that allows brewing at a stable water temperature. (If using a dripper other than resin or if the server is cold, we warm it up.)
The recipes published by THE WORD COFFEE assume the use of a resin HARIO V60 dripper and bleached paper, so rinsing is generally not necessary. However, rinsing may be done as needed for HARIO SWITCH drippers, MUGEN drippers, or other equipment.
Now, let's explore in detail what specific differences and effects exist with or without paper rinsing, based on various research and considerations.
Difference in taste
Generally, rinsed coffee tends to be clean with a sharp acidity, while unrinsed coffee tends to have more body and a milder acidity.
Considering the impact on taste perception
The reason why rinsed coffee feels clean and has a pronounced acidity is not only due to the difference in oil penetration but also has scientific reasons related to taste balance.
1. Masking effect of oil
Coffee oils spread like a film in the mouth, playing a role in softening bitterness and acidity.
• Rinsed → Oil is suppressed, and acidity is felt directly.
• Unrinsed → More oil dissolves, and acidity and sharpness feel milder.
2. Clean cup effect
• When oils and fine particles are caught by the paper, the brewed liquid has a more transparent taste.
• When other flavor elements are reduced, acidity becomes relatively easier to perceive.
• In other words, "acidity stands out because other elements are reduced" rather than "acidity increases."
3. Difference in retention time in the oral cavity
• Liquids with less oil allow water-soluble components to directly touch the tongue, leading to quicker contact with acidity.
• Therefore, it is easy to feel "a sharp acidity."
• Liquids with more oil spread slower on the tongue, and the onset of taste is milder.
→ Result
Rinsed → Reduced oil, clean liquid. Acidity is more prominent.
Unrinsed → More oil, milder acidity, and more emphasis on body.
Let's delve deeper.
Considering surface tension and initial penetration of paper
1. Why rinsing makes it clean
The entire paper already has a water film. The water film creates a "continuous hydrophilic environment," so the coffee liquid that comes later is drawn into the same path (water channel). Oils are blocked by this water film and are absorbed by the paper or tend to remain inside the dripper.
→ Result
The entire paper acts as a "water barrier," making it difficult for oil to pass through.→ A single path controlled by water = clean taste.
2. Why unrinsed coffee tends to have more body
The paper is dry. Air remains in the gaps between the fibers. When coffee liquid comes into contact, due to differences in surface tension, "water goes to gaps that prefer water, and oil goes to gaps that oil can easily enter." This "branching point" ensures a pathway for oil, mixing more oil into the extracted liquid.
→ Result
With the paper fibers still in a disorganized state, "selective pathways" are created during the initial influx of liquid. This allows a small amount of oil to escape and flow into the extracted liquid.Multiple flow paths (water + oil) are created due to differences in surface tension, allowing oil to escape easily = increased body.
In fact, analyses have reported that unrinsed coffee tends to have higher lipid components (such as triglycerides).
Also, while acidic components are primarily extracted in the initial stages of brewing, in the case of rinsing, acidic components are extracted linearly due to the effect of the water film. In the case of no rinsing, they are absorbed to some extent by the paper fibers, so the amount of acidic components extracted is considered to be relatively smaller than with rinsing.
About rib adhesion
One of the purposes of paper rinsing is often said to be to improve the adhesion of the paper to the dripper. However, the original role and purpose of ribs in a dripper with a high-rib structure, such as the HARIO V60 dripper, is to create a gap between the paper and the dripper, allowing air and gases generated during brewing to escape, and stabilizing the flow rate of extraction.
For drippers with high ribs like the V60, we believe that the degree of paper adhesion has little effect on extraction.
In fact, many drippers have recently been developed where the paper does not adhere too closely to the ribs, or hardly touches them at all, and it is not uncommon for baristas using such drippers to win awards in competitions.
On the other hand, for drippers with a special extraction design that have almost no ribs, such as the MUGEN dripper, paper rinsing should naturally be performed.
Conclusion
Whether or not to perform paper rinsing can be determined not only for the purpose of removing paper odor, etc., but also by what kind of coffee taste you desire or want to express.
Considering the fact that the flavor differs depending on the presence or absence of rinsing, as described above, you will be able to gain a perspective and way of thinking to decide whether to rinse based on which method suits your taste better or is closer to the coffee taste you want to express.
Considering THE WORD COFFEE's roasting approach, brewing recipe composition, and concept, and assuming the use of a V60 as mentioned above, we believe that not performing paper rinsing is optimal for expressing the ideal coffee we seek.
I apologize for the length, but I hope this has been helpful.
Summary: How to brew: THE WORD COFFEE/Recipe Collection
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References, partly cited from:
1. Structure and hydrophilicity of paper filters
• It is a common knowledge in materials science and food engineering literature that coffee filters are mainly made of cellulose fibers and have strong hydrophilicity.
• Reference: Research on the hydrophilicity of cellulose in food packaging paper (e.g., Carbohydrate Polymers)
2. Research on oil capture in coffee
• Several papers have shown that paper filters significantly reduce lipids (oils) in coffee.
• Reference: Gross, G. et al., “Cholesterol-raising factor from coffee beans” (J. Lipid Res., 1997)
• This study reported that paper filters almost completely remove oils such as cafestol.
3. Effects of penetration and surface tension
• It is widely known in basic research on capillary phenomena that when liquid penetrates fibrous materials, "which path is preferentially taken" changes depending on the liquid's surface tension and viscosity.
• Reference: Washburn, E.W. (1921). “The Dynamics of Capillary Flow”. Physical Review.
4. Practical knowledge about the effect of rinsing
• While specialized books and barista guides state that "rinsing makes it clean," one of the reasons behind this is thought to be "oil blockage by the water film" in addition to "removal of paper flavor."
• Reference: Scott Rao, “The Coffee Brewing Handbook” and others