"Wet Milling Process vs Dry Milling Process - The Ultimate Guide: Top 5 Differences Between "

Ever wondered why your morning brew tastes so good? Coffee, the world’s favorite wake-up call, goes through a lot before it hits your cup.

The two key players in this journey are “wet milling process” and “dry milling process”. These processes shape your coffee’s flavor, quality, and even its price tag.

But what’s the difference? And why should you care? In this deep dive, we’re spilling the beans on wet vs dry milling. We’ll break down how each method works, their pros and cons, and how they impact your daily grind.

Whether you’re a coffee connoisseur or just curious, stick around. You’re about to become the most knowledgeable person at your local café.

Comparison Table: Wet Milling Process vs. Dry Milling Process in Coffee Production

Wet Milling Process in Coffee Production

Wet Milling Process Overview

Read more about Wet milling process

Wet milling process, often referred to as the washed process, is widely recognized for its ability to produce clean, bright coffee with clear acidity and consistent flavor profiles. This method is commonly used in coffee-producing countries like Colombia, Kenya, and Ethiopia, which are known for their specialty-grade Arabica coffee. The process involves several stages and requires a significant amount of water.

Stages of Wet Milling

1. Selective Harvesting: Wet milling process begins with the selective picking of ripe cherries. Unlike dry milling process, which can use a mix of ripe and unripe cherries, wet milling requires only fully ripe cherries to achieve optimal results. Picking the cherries at their peak ripeness ensures the best flavor​.
2. Pulping: The cherries are transported to a wet mill soon after harvesting. Here, the cherries are pulped using a machine that strips the outer skin, exposing the beans surrounded by sticky mucilage. This step is crucial as it separates the beans from the fruit, removing a major source of unwanted flavors​.
3. Fermentation: Once the cherries are pulped, the beans are placed in fermentation tanks for 12 to 48 hours, depending on temperature and humidity conditions. The fermentation step helps break down the mucilage, and careful monitoring ensures that the beans don’t over-ferment, which can result in undesirable flavors. The length of fermentation and the specific conditions in the tanks can significantly affect the coffee’s acidity, flavor clarity, and body​.
4. Washing: After fermentation, the beans are washed with fresh water to remove the remaining mucilage. Some regions may use mechanical scrubbers for this step, while others rely on water channels to gently clean the beans.
5. Drying: The washed beans, often referred to as “parchment coffee,” are then spread on drying beds or patios to dry. The beans need to reach a moisture content of around 10-12% to be stable for storage and further processing​. Drying can take anywhere from a few days to several weeks, depending on weather conditions. Some mills use mechanical dryers to speed up the process.
6. Storage: Once dried, the beans are stored in their parchment form until they are ready for dry milling, where the parchment layer will be removed.

Advantages of Wet Milling Process

• Cleaner flavor profile: Wet milling process is renowned for producing clean, crisp coffees that allow the inherent flavors of the bean to shine. The fermentation and washing stages remove the fruit and mucilage, which can mask the bean’s natural qualities​.
• Consistency: By carefully controlling the fermentation process and removing impurities, wet milling process can produce more consistent results than dry milling, especially when dealing with large-scale production.
• Higher value: Wet-milled coffees, particularly washed Arabicas, often fetch higher prices on the market due to their clarity of flavor and consistency​.

Disadvantages of Wet Milling Process

• Water consumption: Wet milling process uses vast quantities of water, which is a significant drawback in regions where water is scarce. The process also produces large amounts of wastewater, which must be properly managed to avoid environmental damage​.
• Infrastructure and cost: Wet milling process requires specialized equipment, including pulping machines, fermentation tanks, and drying facilities, which can be costly to set up and maintain. This makes wet milling less accessible to small-scale farmers​.
• Risk of spoilage: If the cherries are not processed within hours of being harvested, there is a risk of fermentation starting prematurely, which can lead to spoilage and off-flavors​.

Dry Milling Process in Coffee Production

Dry milling is the final stage of coffee processing before export and involves removing the parchment layer (for wet-processed beans) or the entire dried cherry husk (for dry-processed beans). It plays a vital role in determining the quality and consistency of the coffee, as it prepares the beans for roasting.

Stages of Dry Milling

1. Hulling: The dry mill receives either parchment coffee or dried cherries. In the case of wet-processed coffee, the parchment layer is removed, while for natural or dry-processed coffee, the entire dried cherry is hulled to extract the green coffee beans. Hulling is typically done mechanically with a machine called a huller​.
2. Polishing (Optional): After hulling, some mills may choose to polish the beans to remove any remaining silver skin. While polishing is mainly aesthetic, it can sometimes affect the beans’ final appearance and market value​.
3. Sorting and Grading: The beans are then sorted by size, weight, and density using a series of screens and air jets. Defective or damaged beans are removed either by hand or using optical sorting machines. This step is crucial for ensuring uniformity in size and quality, which is particularly important for consistent roasting​.Bagging for Export: Once sorted, the beans are packed in jute bags and prepared for export. The beans at this stage are referred to as “green coffee” and are ready to be roasted.

Advantages of Dry Milling Process

• Less water-intensive: Unlike wet milling, dry milling uses very little water, making it a more sustainable option in water-scarce regions.
• Adaptability: Dry milling is flexible and can be used for both wet-processed and dry-processed coffees, making it a versatile option for producers​.
• Cost-effective: Dry milling is generally less costly than wet milling, especially for smaller operations. It requires fewer resources and infrastructure, making it more accessible to farmers with limited capital​.

Disadvantages of Dry Milling Process

• Quality control: Since dry milling often involves processing beans that have undergone different drying methods (natural vs. washed), there can be more variability in quality. Inconsistent drying during the earlier stages can lead to uneven hulling and sorting​.
• Flavor variability: For dry-processed coffees, the prolonged contact with the cherry during drying can introduce more complexity but also more variability in flavor. This can be a disadvantage for producers seeking consistent flavor profiles​.

Key Comparisons Between Wet and Dry Milling Process

Water Usage

Water is a critical differentiator between these two processes. Wet milling process requires vast quantities of water, making it less sustainable in regions where water is scarce. Dry milling process, on the other hand, uses very little water, though it depends on whether the beans were processed using the natural method or the washed method​.

Flavor Profiles

Wet-milled coffees are known for their bright acidity and clean flavors. By removing the mucilage early in the process, wet milling process allows the natural qualities of the bean to take center stage. In contrast, dry-processed coffees tend to have fuller bodies and more complex, fruit-forward flavors due to the prolonged contact between the bean and the cherry during drying​.

Environmental Impact

Wet milling process has a higher environmental footprint due to its water consumption and wastewater generation. This makes it more challenging to implement in regions with limited water resources. Conversely, dry milling, especially for natural-processed coffees, is more environmentally friendly due to its minimal water use​.

Processing Time

Wet milling process is a faster process but requires immediate attention after harvesting. Cherries must be pulped and fermented within hours to avoid spoilage. Dry milling, especially when used after natural processing, is more flexible as the cherries can be dried and processed at a later time​.

Conclusion

In summary, both wet and dry milling play crucial roles in the coffee production process, and each has distinct advantages and disadvantages. Wet milling is ideal for producing clean, consistent coffees but comes with higher costs and environmental concerns due to its water usage. Dry milling, while more sustainable and adaptable, can lead to more flavor variability and requires careful attention to quality control. Ultimately, the choice between wet and dry milling depends on the region, available resources, and the desired flavor profile of the coffee.

By understanding these processes in depth, coffee producers can make informed decisions that not only enhance the quality of their product but also support sustainability and economic viability in their regions.

FAQ

Q1: Why is wet milling more common in specialty coffee production?
Wet milling process is preferred in specialty coffee production because it produces a cleaner, more consistent flavor profile. By removing the pulp and mucilage early in the process, the bean’s natural characteristics are highlighted, making it ideal for showcasing the nuances of high-quality Arabica beans​.

Q2: Does dry milling affect the flavor of the coffee?
Dry milling process itself doesn’t directly influence flavor as much as the earlier stages (like natural processing). However, in dry-processed coffees, where the cherry dries on the bean, the prolonged contact between the fruit and bean can add complexity and fruit-forward flavors​.

Q3: Which method is more environmentally friendly?
Dry milling is generally more environmentally friendly as it uses significantly less water compared to wet milling. Wet milling requires large amounts of water for washing and fermentation, leading to higher water consumption and wastewater concerns​.

Q4: Which process is better for small-scale farmers?
Dry milling process is often more accessible and practical for small-scale farmers because it requires less infrastructure and lower upfront costs. Wet milling process, on the other hand, can be cost-prohibitive due to the need for pulping machines, fermentation tanks, and large quantities of water​.

Q5: What is the impact of wet and dry milling on coffee consistency?
Wet milling process tends to produce more consistent results because the fermentation and washing steps allow for better control over the coffee’s development. Dry milling process, especially for naturally processed beans, can result in more variability in flavor, which some consumers may find desirable for its complexity​.

Sources

• https://www3.epa.gov/ttnchie1/ap42/ch09/final/c9s09-7.pdf