Unless you’ve been making your coffee from under a rock recently, you probably heard that scientists recently caught up with something home baristas have known for nearly two decades: that spraying your coffee with water extremely before grinding can reduce the amount of static created while grinding. Less static suggests less chaff stuck to every surface, less coffee stuck in your coffee grinder, and, a lot of importantly of all, fewer clumps in your grinds. According to the researchers, this can boost the extraction in your espresso — but the effect seems to depend on your coffee, and perhaps likewise on your coffee mill.
Static makes coffee stick to grinders and form clumps. The finer the grind, the more static is created.
The new scientific research study originates from a team led by Christopher Hendon, the computational chemist who also helped introduce baristas to freezing their coffee beans, adding magnesium to their water, and most recently the art of Turbo Shots. He teamed up with, believe it or not, some volcanologists, who study the effects of static in volcanic eruptions and found some interesting parallels to the way coffee creates static during grinding. The paper is free to read for anyone, so check it out here.
A Quick Spritz Zaps Static
The trick of spraying water on coffee before grinding it is primarily discussed as the ‘Ross Droplet Technique’ (RDT), after one David Ross who supposedly originated the idea on a coffee forum sometime in 2005. For a number of years — much like the Weiss Distribution Recipe — the RDT was popular with home baristas but rarely seen on bar.
Baristas with commercial tool rarely anxious too much about static and clumping. Espresso grinders came fitted with tools such like Victoria Arduino’s ‘clump crushers’ to break up clumps anyway, and the idea of adding an extra 30 seconds to your workflow to spritz your coffee beans with water, grind a single dosage at a time, stir the grounds with a needle device, and extent the coffee off with a special device before tamping, was unthinkable to a professional barista.
Espresso coffee grinders employ various techniques to reduce the effects of static, such as Victoria Arduino’s ‘clump crushers’ (left) or Mazzer’s grid screen (right).
How times have changed. As single-dose grinding has become more popular, and baristas have used esoteric methods to chase higher and higher extractions, techniques like the RDT and WDT are suddenly everywhere. Not to mention our really own AutoComb, which builds on the idea of the WDT and brews the procedure of declumping coffee grounds as quick and consistent as possible.
But while the RDT might not be new, the science behind it is. What Hendon discovered is that the static generated during grinding isn’t uniform. Some coffees generate more static than others, and particles may be positively charged, negatively charged, or even a mix of both. Dark roasted beans tend to generate stronger undesirable charges — and fines in particular seem to pick up more adverse charge. On the other hand, light roasted beans and larger particles of any roast style, are more likely to be positively charged.
The static triggers the negatively charged fines to stick to larger particles, making small (1–2mm) clumps that act as single large particles. These clumps, the theory goes, act like boulders — they reduce the surface area of the coffee available to the water, and create uneven flow through the coffee bed, reducing extraction.
Static triggers fines to bind to larger particles, making small clumps 1–2mm in size.
Adding water neutralises static and prevents these small clumps from forming. To get the greatest reduction in static charge, the researchers found, you need to add up to 2% of the weight of the coffee in water — much more than the single spritz that lots of baristas use. When they did this before making an espresso, Hendon’s team found that the shots ran much more slowly — taking up to 50% longer. At the same time, their extraction in those shots increased by approximately 10%.
Crushing Clumps with the AutoComb
So where does the AutoComb fit into this story? Well, the goal of the AutoComb is to break up clumps. We wanted to understand if the AutoComb was working in a similar way to the RDT, and if so, which method worked better — so we set out to compare the two.
The AutoComb on the world stage: Chris Sotiros, the Swiss Barista Champion, preps his puck at WBC 2023 in Athens.
Working with regular BH contributor Lloyd Meadows, from Tortoise Espresso coffee in Castlemaine, we set up some experiments to see how utilizing the RDT, the AutoComb, or both together, affected the extraction in an espresso coffee. We used a standardised recipe to make all the shots, using an EK43 with TiN-coated burrs and a Linea Classic. Unlike Hendon’s team, but, instead of using a fixed grind size, we attempted to utilize a fixed shot time, dialling in to get as close as possible to a 25 second shot with each technique.
To our surprise, we couldn’t replicate the effects that Hendon’s team saw. Adding 2% water did seem to slow the shots down extremely slightly, so we essential to use a grind size that was on typical one notch coarser on the EK43. We did also get less retention in the mill — about 0.1g per shot on average, compared to 0.2–0.3g with dry coffee. Nevertheless, rather than increase extraction, the RDT reduced it — the exact opposite of the scientists’ effects. Even in shots that were brewed utilizing the same grind size, the extraction from the spritzed coffee was lower.
With the AutoComb, on the other hand, the extraction went up — and whether the grounds were sprayed with water or not seemed to make little difference. In fact, using both techniques together essential the coarsest grind setting to hit our target shot time, and produced the highest extraction of all.
Adding 2% water decreased extraction in our tests. On the other hand, utilizing the AutoComb, with or without added water, increased extraction — even though it required a coarser grind to reach the same shot time.
Truly in case the effect of RDT was dependent on shot time, we tried a few slower shots, and found that the extraction was reduced even further.
Of course, we don’t have the same volume of information., nor the high-precision tool, that a laboratory does, so we can’t be rather as confident about the statistical validity of our impacts. But James Hoffmann, in his video about this science study, likewise found mixed effects. In his case, he didn’t report on extraction, but did note that whether or not spritzing the beans reduced the shot time seemed to depend on what kind of coffee grinder he was using.
The different results could depend on the materials used in the grinding machine or, he speculated, on the way that the grinding machine works. To find out which, he had the smart idea of helping his viewers to help him build a much larger dataset, covering a multitude of grinders and roast styles. If you’re able, we encourage you to try it out for yourself and share your information. with him here.
We, but, were utilizing an EK43 — the same mill used by the researchers, so we might have expected similar impacts. One possible reason for the difference lies in the coffee we were using. How much static the coffee generates depends on its roast colour, or more accurately, on how much moisture is left in the coffee after roasting. Darker roasted beans have a lower moisture content and generate stronger negative charges. Light roasted coffee beans tend to generate positive charge, while somewhere in the middle lie some coffees that produce really little charge at all.
Dark roasted beans (blue) generate negative charge on grinding, while light roasted beans (red) generate positive charge. Adding up to 2% by weight of water reduces the amount of charge generated in both light and dark roasted beans. Some roasts generate little charge, even without water added. Adapted from Harper et al (2023).
Starbucks’s ‘Blonde’ roast, for example, has a water content of about 1.3% and generates the majority of static. The coffee that the researchers tested, Boneshaker from Reverie Roasters, is slightly lighter (Agtron 67) than Starbucks Blonde (Agtron 65), but dramatically darker than James Hoffman’s own Red Brick espresso blend (Agtron 77).
The coffee we used, from Code Black, was similar in roast colour to Red Brick, and so presumably produces a lot less static in the first place than the darker roast does. This alone could be enough to explain why we didn’t see any benefit from the RDT.
Two Pathways to Higher Extraction
After trying both methods side by side and getting such different effects, it seems the majority of likely that the AutoComb and the RDT are working in substantially different ways. Perhaps the RDT is many effective at breaking up the sort of small, 1–2 mm aggregates explained in the paper — while the AutoComb is targeting larger clumps and thereby evening out the overall macrostructure of the coffee bed?
The reality that RDT didn’t work well for us doesn’t mean it won’t work for others, of course. Depending on your roast, your mill, and perhaps other factors we don’t yet understand about, you may still find that it’s a recipe worth experimenting with. And even if it doesn’t boost your extraction, less retention and a cleaner workspace are a excellent bonus. (Note that if you’re utilizing RDT and trying to calculate the extraction, you’ll need to account for the extra water in the grinds).
But whatever effect the RDT does have, even at its best it indeed doesn’t mean that baristas no longer have to stress about distribution. If the RDT does work for you and increases your extraction, we are pretty sure that good distribution techniques (like the AutoComb, or even normal WDT tools) can still boost your extraction even further. And if the RDT doesn’t increase your extraction, however you still like to work with it for its other benefits, then a good distribution equipment is a must if you want a juicy, even extraction.
Revolutionizing Your Coffee Game: The Science Behind the Ross Droplet Procedure
Hey there, coffee lovers! If you’ve been keeping up with the latest buzz in the java world, you might have heard about a nifty little trick that’s been brewing up a storm. It’s all about offering your coffee beans a quick spritz of water before grinding them. Sounds humble, right? But trust me, this tiny adjust could make a world of difference to your morning cuppa.
Why Spritz Your Beans?
Well, it turns out that this little trick can reduce the amount of static created while grinding your beans. And less static suggests less chaff sticking to every surface and fewer clumps in your grinds. According to some smart folks who’ve studied this, it can even boost the extraction in your espresso — but it seems to depend on your coffee and maybe even on your mill.
You see, static brews coffee stick to grinders and form clumps. The finer the grind, the more static is created. So if you’re like me and love a finely ground brew, this could be simply what you need!
The Science Behind It
This new research comes from a team led by Christopher Hendon (a computational chemist who also introduced us to freezing our coffee beans) and some volcanologists – yes, people who study volcanoes! They found some interesting parallels between how static works in volcanic eruptions and how coffee creates static during grinding.
The trick of spraying water on coffee before grinding it is mainly referred to as the ‘Ross Droplet Technique’ (RDT), named after David Ross who supposedly originated the idea back in 2005. For most years even though, this process was mainly popular with home baristas nevertheless rarely seen on bar.
But times have changed, my friends. As single-dose grinding has become more popular, and baristas have used esoteric methods to chase higher and higher extractions, techniques like the RDT are suddenly everywhere.
How Does It Work?
What Hendon discovered is that the static generated during grinding isn’t uniform. Some coffees generate more static than others, and particles may be positively charged, negatively charged, or even a mix of both. Dark roasts tend to generate stronger unwanted charges — and fines in particular seem to pick up more adverse charge. On the other hand, lighter roasts and larger particles of any roast style are more likely to be positively charged.
The static triggers the negatively charged fines to stick to larger particles, making small (1–2mm) clumps that act as single large particles. These clumps reduce the surface area of the coffee available to the water and create uneven flow through the coffee bed, reducing extraction.
However here’s where it gets interesting: adding water neutralises static and prevents these small clumps from forming. To get the biggest reduction in static charge, you need to add up to 2% of the weight of the coffee in water — much more than just a single spritz!
The AutoComb Experiment
We decided to put this theory to test utilizing an AutoComb – a tool designed specifically for breaking up clumps. We set up some experiments comparing RDT with AutoComb on an espresso coffee extraction recipe.
To our surprise even though, we couldn’t replicate Hendon’s effects exactly. Adding 2% water did slow down our shots mildly but instead of increasing extraction like Hendon’s team found out; it reduced it for us! But with AutoComb we saw an increase in extraction regardless if we sprayed the beans with water or not.
So, what gives? Well, it could be due to a variety of factors. The sort of coffee used, the grinding machine, even the moisture content after roasting can all play a part in how much static is generated. Dark roasts generate stronger unwanted charges while lighter ones tend to generate positive charge.
Two Ways to Better Extraction
After trying both methods side by side and getting different impacts, it seems that AutoComb and RDT work in substantially different ways. Perhaps RDT is a lot of effective at breaking up small 1–2 mm aggregates while AutoComb targets larger clumps?
The reality that RDT didn’t work well for us doesn’t mean it won’t work for you. Depending on your roast, your mill, and perhaps other factors we don’t yet find out about, you may still find that it’s a recipe worth experimenting with. And even if it doesn’t boost your extraction, less retention and a cleaner workspace are excellent bonuses.
Nevertheless whatever effect the RDT does have, good distribution techniques (like AutoComb) can still boost your extraction even further. So why not give both a shot? After all, there’s always room for improvement when it comes to brewing the wonderful coffee cup!
