Should we all be using the Weiss Distribution Technique again? Is there a right way and a wrong way to do it?

The Weiss Distribution Technique (WDT) is a distribution method for espresso making. Using a fine needle or similar tool, the barista stirs the coffee while it sits in the portafilter. A funnel placed above the portafilter helps prevent spills. The stirring action breaks up any clumps, and evens out the density of coffee within the puck. The result is reduced channelling, and higher, more even extractions.

The Weiss Distribution Technique in action.

The WDT is named for John Weiss, who developed the technique back in 2005 as a way to compensate for grinders, especially smaller home grinders, that produced excessive clumps. The WDT became well-known among home baristas, and has been written about extensively in the years since.

Commercial and ‘prosumer’ grinders generally include features designed to break up large clumps and distribute the coffee more evenly into the basket, directly from the grinder. While some grinders achieve this more effectively than others, it was generally thought to make the WDT unnecessary. For this reason, and also because of the time it adds to the workflow, the WDT is very rarely used by professional baristas.

More recently, the detailed analysis of espresso techniques made possible by pressure or flow-profiling machines like the Decent, have brought the WDT back into the limelight. By measuring pressure and flow inside the puck, we can see which techniques produce a more stable puck, and which are more prone to cause microchannelling. By this measure, the WDT seems to be highly effective.

What Does WDT Do?

Perhaps the person most responsible for bringing discussions of WDT back into the mainstream is Scott Rao, who used versions of the technique as part of a strategy to achieve very high extractions. We asked him what it was that convinced him that the WDT was the most effective distribution method.

A WDT tool. Several manufacturers sell tools like this one, designed to make the Weiss Distribution Technique easier and faster.

“The most compelling evidence for the efficacy of WDT is reduction in channelling,” Scott says. “When you use WDT well, you cannot only see a decrease in channelling but all else being equal, your shots should flow a little slower, which is a side effect of decreased channelling.”

Channels can be detected by looking at extraction curves. Increased resistance in the puck is an indication that the particles are packed more closely together, which is a key characteristic of a well-distributed puck. In a flow profiling machine, higher resistance leads to higher pressure at the puck.  “With WDT, we can see shots have a higher peak pressure and sustain it longer,” writes John Buckman, the inventor and owner of Decent Espresso. “The improvement in shot quality is obvious.”

The real test is the flavour and consistency of the shots made using the technique, however. “In the cup, using WDT should decrease the average amount of bitterness and astringency, and should make shot times and extraction levels less variable,” Rao says.

What is the Optimal Technique?

The first consideration when adopting WDT is using the right tool. Our testing has shown that anything more than 1mm in diameter is counterproductive, so a toothpick, for example, would not be suitable.

It’s also important to stir carefully and evenly throughout the bed. “It’s easy to cause uneven density throughout the coffee bed if you do WDT sloppily or too aggressively,” Rao says.

There is debate about whether it is preferable to stir only the grounds at the surface, sometimes called ‘puck raking’, or to stir right to the bottom of the basket, referred to as ‘deep WDT’. In a recent White Paper published on Barista Hustle, coffee blogger (and astrophysicist) Jonathan Gagne compared the two methods, using puck resistance as a measure of how effective the technique was.

He found that stirring right to the bottom of the puck led to higher puck resistance overall, and more importantly, less variation in the resistance from one shot to the next. This suggests that deep WDT is more effective than puck raking.

While deep WDT may be more effective, both techniques are effective compared to other distribution methods, and puck raking is easier, Buckman argues. “Gagne’s results are convincing, but the improvement going to the bottom is slight”.

Nonetheless, the difference in effectiveness was enough to convince Rao, who had previously argued that puck raking was superior. “The reason I believed that for a little while was likely because I wasn’t doing the WDT well enough,” Rao says.

Should Professional Baristas Adopt WDT?

The difficulties Rao acknowledged in developing a deep WDT workflow point to one of the issues with using the technique behind a bar: namely that it takes time and attention to do correctly. “With manual WDT, it is difficult to achieve consistency,” says BH founder Matt Perger. This is likely to be a barrier to adoption for a lot of coffee bars, where speed and consistency are paramount.

However, the higher extractions that can be achieved with optimal techniques have two big advantages: the flavour is likely better, and less coffee needs to be used to make the same drink. “With attention and care you can get a lot farther with WDT than almost any other method,” Perger says.

A distribution tool. Distribution tools like this create a flat surface for tamping, but generally do not seem to affect the distribution of coffee lower in the puck.

This means that WDT, or a well-designed tool that automates the process, could find a place in high end coffee bars soon. After all, a lot of espresso bars currently include an extra step in their workflow in the form of a ‘distribution tool’, despite the lack of evidence that distribution tools are effective. “Most of the ‘distribution tools’ out there do not re-distribute the coffee,” Rao says. “They are effectively tampers. WDT is unique in that it has the ability to break up clumps and re-distribute the coffee bed from top to bottom.” Replacing this step with some form of WDT, so long as it’s carried out correctly, has the potential to improve quality and consistency behind the bar.