Why Spray Water Before Grinding Coffee Beans? Can RDT Really Make Coffee Taste Better?

Introduction to RDT: Ross Droplet Technique

Believe it or not, you've likely seen various "special techniques" for coffee preparation on different media platforms or in FrontStreet Coffee's articles. For example, digging a small hole in the center of the coffee bed or performing "acupuncture" on the coffee grounds – these are various auxiliary methods invented by industry experts to craft a better cup of delicious coffee!

Besides these commonly seen methods in daily practice, there's another technique called "RDT" that can also assist us in making a delicious cup of coffee.

Understanding Static Electricity in Coffee Grounds

As we all know, coffee beans are very prone to generating static electricity during the grinding process. This is caused by friction between coffee beans and grinder blades, as well as uneven charge distribution during the cracking process of the beans. The darker the coffee beans are roasted (lower moisture content) and the finer they are ground, the more static electricity will be generated during grinding. The presence of static electricity creates adhesion in coffee grounds, causing finer, lighter particles to adhere to larger particles and form clumps.

When coffee grounds clump together, their surface area for water contact decreases, which will lead to a reduction in coffee extraction rate. At the same time, clumped coffee grounds can easily promote channeling effects, especially in espresso extraction. Water flow is likely to bypass the clumped coffee grounds and focus on extracting the surrounding areas with relatively looser texture. This will result in extremely uneven coffee extraction, which is what we commonly call the channeling effect. If we need to consistently make a good cup of coffee when there are many clumped coffee grounds, we need to use some auxiliary methods to eliminate the impact of static electricity. Besides the distribution needles mentioned by FrontStreet Coffee a couple of days ago, there's also "RDT" implemented before grinding coffee beans.

What is RDT?

So-called RDT is short for Ross Droplet Technique, which translates to "Ross Droplet Technique." It first appeared in 2005 on a coffee forum called "Alt.Coffee." Although it sounds quite sophisticated, this method actually only requires spraying water on coffee beans or moistening them. With just this simple operation, we can reduce the occurrence of clumped coffee grounds and lower the probability of channeling during coffee extraction. Since the person who invented this method is named David Ross, people named this technique the Ross Droplet Technique, abbreviated as RDT.

Scientific Validation and Practical Considerations

At the end of the year before last, the latest paper published by the University of Oregon in the journal "Matter" also confirmed this theory. FrontStreet Coffee has also verified through practice that spraying water on coffee beans can indeed effectively reduce clumping and decrease the adsorption phenomenon of coffee grounds. Therefore, we can learn that RDT is indeed a feasible optimization solution. However, the RDT method still has certain drawbacks, which prevent it from being well-suited for daily coffee production in coffee shops. There are two main reasons: one is that RDT is only suitable for "single-dose" coffee beans and is difficult to apply in batch processing. From the moment water spray contacts the coffee beans, they begin to absorb moisture. Although slowly, the flavor compounds in the coffee beans have already started to decompose, which requires us to grind and use this moistened coffee powder within a short time, otherwise the coffee's aroma will be greatly diminished.

Therefore, RDT is difficult to use in situations with high cup production volumes, as it will significantly increase the time cost of coffee making, greatly reducing efficiency. Moreover, the main objects affected by clumped coffee grounds are espresso. For espresso, coffee shops that only use "single-dose" coffee beans at one time are few and far between. Using distribution needles would be more practical.

Proper Application of RDT

Secondly, the water quantity control for RDT actually requires relatively high precision. Spraying too little won't have much effect, while spraying too much will instead make coffee grounds more prone to clumping due to moisture, and this type of clumping can even have more negative effects than those caused by static electricity. In addition, when grinder burrs have long-term contact with water without timely cleaning, there's a probability of rust occurring. In other words, when we use it improperly, it's easy to suffer losses that outweigh the gains. Therefore, FrontStreet Coffee does not recommend using RDT without proper guarantees. If there are indeed many, many clumped coffee grounds and RDT is really needed to reduce the amount of clumping, then FrontStreet Coffee would more highly recommend the method shared by coffee guru James Hoffmann: dip a spoon handle into water, then use the water-beaded spoon handle to quickly stir the coffee beans. When the coffee beans are roughly evenly coated, you can start grinding. If not, then distribution needles would be a safer option~

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