“Using Wet Weiss Method for Espresso Preparation: A Guide for Baristas”

About six months ago, Dan Shusett from Tricolate introduced us to the idea of Wet Weiss Distribution — that is, using a Weiss distribution device to stir wet coffee grounds during brewing. It turns out that Wet Weiss Distribution is surprisingly effective — not literally in no-bypass brewers like the Tricolate, but likewise in conventional filter brewers like the V60.

Traditional stirring methods, with a spoon or spatula, can increase extraction, at the cost of slowing down the brew time. In extreme cases this leads to choking and channelling, making a bitter, ashy brew.

On the other hand, using the fine needles of a Weiss distribution equipment to stir the bloom or the slurry in your brewer can increase extraction without causing the brew time to slow down. Wet Weiss can therefore give you increased extraction without an increased risk of channelling. So if you haven’t already adopted this recipe for your American coffee, then you must probably give it a try.

Naturally, though, our experiments didn’t end there. The Weiss Distribution Technique was, after all, invented for espresso coffee — why wouldn’t Wet Weiss work for espresso as well?

The answer is that it doesn’t. Actually, it was a disaster. First of all, there are some practical difficulties: For example, have you ever tried tamping wet coffee? It isn’t easy! But even when we solved these problems, we found that the Wet Weiss procedure crafted it more or less impossible to brew a tasty espresso.

However, utilizing Wet Weiss in espresso did raise some interesting questions about what takes place inside an espresso coffee puck when we tamp, and how preinfusion and ‘blooming’ work in espresso coffee. It also means one reason why high humidity conditions can cause such problems for baristas.

Wet Weiss and Jamming

As with all our perfect and wildest experiments, our investigation of Wet Weiss for espresso coffee began with a conversation with multidisciplinary industrial scientist Professor Abbott. He shown that adding some water before tamping might allow us to pack the bed of coffee more tightly together.

Back when we were researching our Advanced Espresso course, we were exploring the scientific research of ‘jamming’ and how it relates to coffee. Jamming explains how powders — like ground coffee — can form structures that resist forces on them — like tamping.

Loose powders can flow, in a similar way to a liquid. Under certain conditions, the particles in a powder can form structures, such as arches, that ‘jam’, or block the flow.

Sand particles in an hourglass can spontaneously form an arch structure, causing the flow of sand through the hourglass to jam.

The same principle limits how tightly coffee can pack together in an espresso coffee puck. When you tamp the ground coffee, the puck compresses up to the point that the particles connect and become jammed. After that, tamping harder has no further effect on the structure of the puck.

In several circumstances, adding water helps overcome jamming. A small amount of water can create ‘capillary bridges’ and cause particles to stick together — as anyone who has tried to pour damp salt out of a shaker knows. On the other hand, if you add a larger amount of water — when mixing cement, for example — it functions as a plasticiser. A plasticiser stops particles from sticking together, and allows them to move more freely.

In coffee, moisture also has an additional effect: it steeps coffee’s cell walls more flexible (Mateus et al 2007), allowing the particles to deform more easily. This would make it easier for the tamping force to break up a jam in the ground coffee.

Between these two results, we thought there was a good chance that adding some moisture before tamping might allow us to create a super-dense coffee puck. Furthermore, we wondered if creating a super-dense puck this way — if it turned out to be possible — would reduce channelling or boost extraction.

The Wet Tamping Challenge

The first problem to overcome was how to tamp wet coffee without it sticking to the puck. The most effective process we found was to work with cling film on top of the wet coffee. 

We began by mixing ground coffee with boiling water in a cup, using the Comb WDT device to ensure the water and coffee were fully mixed. We scooped the wet coffee into a portafilter basket, stirred with the Comb again to ensure even distribution, then laid a layer of cling film on top before tamping.

A layer of cling film is required for tamping wet coffee

Once the coffee was tamped, we could gently peel off the clingfilm, leaving a perfectly tamped, wet puck.

With this problem solved, we started pulling shots, and almost immediately realised that wet tamping was not going to work the way we had hoped. The shots literally flew through the machine, no issue how finely ground the coffee was. We were creating the espressos utilizing a well-aligned EK43, with the burrs touching, and still getting incredibly quick shot times.

The extraction was similarly dismal — even when creating espressos with yields of up to 60 grams, the highest extraction we were able to achieve was about 20% lower than that of a representative espresso coffee brewed at a 1:2 ratio. This is even more striking when you consider the extended contact time between water and coffee while creating these espressos, thanks to the time taken to stir the wet coffee. Whatever effect water was having on the puck prep, it was clearly not what we had hoped. 

Inside the Puck

To see if adding water was having any effect on the structure of the puck, we started by measuring the puck height after extraction, utilizing the same dosage and grind size for wet and dry tamping. The wet-tamped and dry-tamped pucks were the same height, to within a tenth of a millimetre. This clearly implies that the added moisture wasn’t having much effect on the overall packing density.

We also cut the two pucks open, to see if we could see any difference in the structure of coffee inside the puck. At first glance, no major differences were apparent between the two pucks.

Left: a conventional, dry-tamped puck. Right: a wet-tamped puck

Zooming in on the pictures, however, revealed a possible difference. The dry-tamped puck looks muddier, as if it had retained more fines. The wet-tamped puck, meanwhile, appeared to have a more open texture.

Left: the muddy texture inside the dry-tamped puck. Right: the looser texture of the wet-tamped puck

The act of cutting the puck inevitably disturbs the structure, so we’re cautious about reading too much into a slight visual difference like this by itself. To see if there was any difference between the particles retained in each puck, we ran a particle size analysis. We took a thin slice across the centre of each puck, dried the particles, and separated them out on a lightbox. We analysed the size distribution across four separate images.

Analysing the particle size distribution

We found that, considered on the area or volume basis, the wet-tamped coffee had a mildly smaller average particle size than the dry-tamped coffee. The difference was slight but statistically significant.

Particle size diameter of wet and dry-tamped pucks. The surface area and volume basis measurements were significantly different (T-test, p<0.05)

Since this test is only based on photos of the same sample of coffee, it can only confirm the difference between these two samples — it would take a lot more analysis to extend this to wet and dry-tamped coffee in general. It does, nevertheless, contradict the idea that the dry puck is retaining more fines, as the images initially shown.

The texture difference we noticed could just be an artefact, an apparent difference caused by the way the coffee was cut — or it could be something else totally. When we cut open the pucks, we did notice that the particles in the dry-tamped puck were stuck together much more strongly than in the wet-tamped puck. However, there’s no way to be sure if this relates to differences in the structures formed during tamping, or due to the unextracted material left behind.

Barriers to Flow

So if there isn’t a clear structural difference between the pucks, why is the flow rate so different? Two possible candidates are the hydrophobic nature of dry coffee, and the gases trapped inside the particles.

Dry coffee naturally resists the flow of water due to the reality that it is hydrophobic, compared with wet coffee. This is similar to what takes place when you water a totally dry pot plant — at first the water pools on top of the soil, or bypasses the soil completely. The soil can only absorb the remaining water when it is already mildly damp.

The gases trapped inside dry coffee also seem to block the flow of water through the puck. This is why freshly roasted coffee needs a coarser grind than old coffee — it contains more trapped gases, which limits the flow of the espresso (though the story is a little different when the coffee is very fresh).

One clue to which of these factors is more important came when we repeated the wet tamping experiment, nevertheless using cold water to wet the coffee grounds initially. In this case, the difference in shot time was much lower. If the difference in shot time was only due to the dry coffee being hydrophobic, then we would expect cold water to have a similar effect.

On the other hand, the degassing rate is associated with temperature (Smrke et al 2017) and hot water seems to cause coffee grounds to release trapped gases more quickly than cold water does. Using cold water to pre-wet the grounds thereby reduces the effect on shot time, because the coffee has degassed less before brewing. However, the espresso coffee crafted this way still has a noticeably ‘stale’ aroma, which we assume is due to volatile flavors being lost when wetting the coffee.

On a whim, we also tried using steam to pre-wet the coffee grounds. In this case, the flavors coming off the coffee grounds during the pre-wet stage — aromas that would be missing from the espresso coffee — were very potent. The resulting espresso coffee gushed out in a question of seconds, and had virtually no crema at all.

All in all, it seems the majority of likely that the effect of degassing is what caused this experiment to fail. It likewise indicates one reason why preinfusion is so helpful in improving the quality of espresso coffee. In espressos crafted with pre-infusion (or the more extreme ‘blooming’ espresso) degassing allows a faster flow, and hence, a finer grind — without flavors being lost to the atmosphere as easily as wetting the grinds in the open air.

Humidity in Espresso coffee

The effect of humidity can be seen in coffee stored under humid conditions. James Hoffmann explored the effect of humidity on filter brewing in a video exploring earlier experiments by Hamad Rahsid, and found that coffee stored at high humidity had a smaller bloom and a much faster flow rate in a V60 than coffee stored in dry conditions. Similarly, coffee that is ‘quenched’ (cooled) with water at the end of the roasting technique, which has a higher moisture content, degasses faster than air-cooled coffee (Baggenstoss et al 2007).

Robert McKeon Aloe expanded on this idea for espresso, and found that humidified coffee required a much finer grind setting to achieve reasonable shot times, and that the resulting shots had much less crema. All of this points to degassing as being an important part of the effect of humidity on espresso.

Humid conditions could cause faster degassing by making the coffee structure more flexible, allowing gases to escape, explains Professor Abbot, saying: “I think the humidity is making the particle walls more mobile (i.e. lowering the glass transition temperature) so the diffusion rate of CO2 increases.”

Other factors play a part in the effect of humidity, too: humid beans are less brittle, and therefore produce less fines when they are ground (Baggenstoss et al 2008). This indicates that humid beans ought to be ground at a finer setting to achieve the same shot time. Our experiments show, but, that grind size is not the only factor.

As to how to pack your puck more tightly? Well, we’re still working on it. There are a multitude of contradictory factors that affect jamming, and unpicking the impacts of each is extremely difficult. “The scientific research of how dry particles behave is lamentable,” Professor Abbott explains. “This suggests that what takes place when you dry tamp is a whole set of complicated unknowns and there aren’t any good ways to measure those unknowns anyway.” Professor Abbott did, but, come up with a new potential procedure to better understand tamping which we’re hoping to explore soon — so watch this space.

There are still plenty of factors to explore in our attempt to create the perfectly tamped bed of coffee — however we can be fairly clear that, as far as espresso coffee goes, it’s best to keep your powder dry.

Revolutionizing Coffee Brewing: The Wet Weiss Distribution Technique

Hey there, coffee lover! Have you ever heard about the Wet Weiss Distribution process? If not, buckle up because we’re about to take a deep dive into this brewing process that’s been stirring up rather a buzz in the coffee world.

The Magic of Wet Weiss Distribution

About half a year ago, our friends at Tricolate introduced us to this intriguing concept. It involves using a Weiss distribution device to stir wet coffee grounds during brewing. Sounds modest enough, right? But wait till you hear how it can transform your caffeinated drink!

This recipe has suggested to be surprisingly effective – not just in no-bypass brewers like the Tricolate but likewise in conventional filter brewers like the V60. Now, I know what you’re thinking: “Doesn’t stirring with a spoon or spatula do the same thing?” Well, yes and no.

Traditional stirring methods can certainly increase extraction however often at the cost of slowing down the brew time. In extreme cases, this leads to choking and channelling which effects in a bitter, ashy brew – and nobody wants that!

But here’s where Wet Weiss shines. Using the fine needles of a Weiss distribution equipment to stir the bloom or slurry in your brewer can increase extraction without causing the brew time to slow down. This indicates you get increased extraction without an increased risk of channelling. So if you haven’t already adopted this recipe for your American coffee, then it’s high time you gave it a try.

The Espresso coffee Experiment: A Twist in The Tale

Naturally even though, we didn’t stop there. We thought: “The Weiss Distribution Technique was invented for espresso — why wouldn’t Wet Weiss work for espresso as well?” Well, let’s simply say it was a little of a disaster.

First off, have you ever tried tamping wet coffee? It’s like trying to wrangle a slippery eel! But even when we managed to overcome these practical difficulties, we found that the Wet Weiss technique made it more or less impossible to brew a tasty espresso. Talk about a plot twist!

But, this experiment did raise some interesting questions about what takes place inside an espresso puck when we tamp, and how preinfusion and ‘blooming’ work in espresso. It also gave us insights into why high humidity conditions can be such a headache for baristas.

The Science of Coffee: Wet Weiss and Jamming

Our investigation of Wet Weiss for espresso coffee began with an enlightening conversation with multidisciplinary industrial scientist Professor Abbott. He suggested that adding some water before tamping might allow us to pack the bed of coffee more tightly together.

This concept is based on the science of ‘jamming’ which explains how powders — like ground coffee — can form structures that resist forces on them — like tamping. In several scenarios, adding water helps overcome jamming by creating ‘capillary bridges’ causing particles to stick together or acting as a plasticiser allowing particles to move more freely.

Intriguingly, moisture likewise makes coffee’s cell walls more flexible allowing the particles to deform more easily. This would make it easier for the tamping force to break up a jam in the ground coffee. So we thought there was a good chance that adding some moisture before tamping might allow us to create a super-dense coffee puck.

The Wet Tamping Challenge

The first hurdle was figuring out how to tamp wet coffee without it sticking everywhere. The the majority of effective procedure we found was to utilize cling film on top of the wet coffee. Once the coffee was tamped, we could carefully peel off the clingfilm, leaving a perfectly tamped, wet puck.

With this problem solved, we started pulling shots and almost immediately realized that wet tamping wasn’t going to work as we had hoped. The shots literally flew through the machine, no question how finely ground the coffee was. The extraction was similarly dismal — even when creating espressos with yields of up to 60 grams, the highest extraction we were able to achieve was about 20% lower than that of a traditional espresso coffee crafted at a 1:2 ratio.

Inside the Puck: A closer look

To see if adding water was having any effect on the structure of the puck, we measured the puck height after extraction using both wet and dry tamping methods. Surprisingly, there wasn’t much difference in overall packing density.

We likewise cut open both pucks to see if there were any structural differences inside. At first glance, no major differences were apparent between the two pucks. Nevertheless, upon closer inspection and particle size analysis, it seemed that wet-tamped coffee had a slightly smaller average particle size than dry-tamped coffee.

The Verdict: Keep Your Powder Dry

So what’s our takeaway from all these experiments? Well, it seems the majority of likely that degassing is what caused this experiment to fail. It likewise means one reason why preinfusion is so helpful in improving espresso coffee quality – it allows for faster flow and hence a finer grind without losing tastes as easily as when you wet your grinds in open air.

As for how to pack your puck more tightly? We’re still working on it! Nevertheless one thing’s for sure – when it comes to espresso coffee, it’s perfect to keep your powder dry. So there you have it, folks! The next time you’re brewing a coffee cup, why not give the Wet Weiss Distribution procedure a try? You might literally find out a whole new world of tastes!