Descale Like a Pro: Understanding and Conquering Scale in Any Coffee Machine

Water is a complex substance. Known as the universal solvent, water has the power to dissolve almost anything over time. That means that as water travels—through reservoirs, lakes, and bodies of water, it picks up molecules from the objects it interacts with. Most water has some level of dissolved minerals and other compounds.

Water is also the base for all coffee drinks. Espresso is about 95% water, while drip coffee is over 98% water.

As heat and pressure are applied, water will let go of some of the molecules that it’s dissolved. Espresso machines and other coffee brewing devices apply heat and pressure to water—that’s how espresso is made. So as time goes on, more and more of these dissolved solids will evaporate from your water and end up in your espresso machine. And that’s called scale.

Is this your first time hearing about scale and your coffee machine? Don’t worry—although most people don’t know what scale is, scale a common problem for almost any piece of coffee equipment. and We're here to talk you through what scale is, and how to deal with scale on your coffee brewing equipment.

What Exactly Are We Talking About?

If this is your first time reading about scale, don’t worry—even coffee experts have been confused about scale.

“For the longest time I didn't know what scale was,” says Andrew Bettis, education and development manager for Rancilio North America. “I thought scale was coffee buildup inside the machine, but espresso machines have systems that keep coffee from building up inside the machine.”

Scale is when limestone builds up in your coffee brewer. “When water moves through bedrock as groundwater, it will dissolve limestone. And so limestone is usually calcium carbonate, or CaCO3,” says Andrew.

When water heats and expands, the minerals it picks up as it moves through bedrock disassociate. The minerals then hang onto the surfaces they interact with, slowly building up over time. Scale is that build up—hardened calcium and other minerals that can affect both the taste and performance of your brewing equipment.

You’ve likely seen scale in some form, usually around a faucet or a shower knob. But it can be difficult to see scale on your coffee brewer. Scale builds up slowly and usually builds in places you might not be able to see well within your machine.

Because scale is hard to detect visually, you need to have a regular descaling schedule.

Now Is The Time

How can you tell when it’s time to descale your machine?

“There are usually a couple of clues that can tell you if your coffee equipment is in need of a descale,” says Melissa Vaiden, coffee technician for Counter Culture Coffee in New York City. “In my experience, scale typically builds up quicker on espresso machines than coffee brewers/kettles. On an espresso machine, it's a bit hard to tell if things are building up scale because opening up the boiler is a pretty tedious task.”

Even though espresso machines are trickier to diagnose, Vaiden says there are a few signs to watch out for. “If you notice your group head putting out less water over time and/or clogging all together frequently, it's probably fair to say that you are having some scale issues,” she notes. “For brewers, if you can open it up and see into the boiler then you should be able to visibly see the scale.”

Along with slower brewing times, other signs of scale can be weird sounds or your brewer taking a lot longer to get to temperature than usual. But descaling your machine is more a matter of preventative maintenance—technicians like Vaiden and Bettis recommend that you get your machine on a regular descaling schedule.

So, if you’re reading this article and you can’t remember the last time you descaled your machine, the time is now.

Watch the Water

Although we’re talking about scale, Bettis points out that there’s more to the story. “A conversation about scale is really a conversation about water.”

“Water basically exists in two states of being: either soft or hard,” he says. “I actually like to think of water almost like a toxic relationship. Water either has a lot of baggage that it comes with or it shows up and wants to consume a lot.”

To use Bettis’ analogy, water with a lot of “baggage” is hard, or has a high number of total dissolved solids, or the minerals that contribute to scale build up. On the other end, soft water has a lower amount of dissolved solids, so scale builds up slower if the water is softer.

To determine the water hardness in your area, you can buy test strips that tell you the parts per million (ppm) of dissolved solids in your water. You can also check your city or town’s municipal information. Most cities will collect and publish reports about where water is coming from and how hard or soft the water is.

Certain areas are more prone to hard water than others. If you live in an area with hard water, you can buy water softeners or invest in a water filtration system. A softener or a filter will reduce the number of dissolved solids and slow down the buildup of scale.

Water quality isn’t the only thing contributing to scale. “Another factor that could accelerate scale buildup would be the frequency of use the machine gets,” says Vaiden.

However, the relationship between frequency and scale isn’t always linear. A machine that goes dormant can actually build up scale more quickly than one in constant use. “I would recommend using the machine at least every couple of days to keep water from sitting for a prolonged amount of time,” Vaiden suggests. “Cycling freshwater through the system will keep scale from wanting to build up.”

What Happens When You Don’t Descale?

It might seem like soft water, or maybe even distilled water (which has no dissolved solids) would be better for your coffee brewer, right? You could avoid scale altogether.

“It’s much better to have slightly harder water because it is much easier to descale a machine than fix a corroded piece of equipment,” says Bettis. Remember what he said about water? It either leaves things behind (hard water leaves scale) or it takes away. If there aren’t enough dissolved solids in water, the water will start to corrode away your equipment. Once your equipment starts to oxidize and corrosion occurs, you can’t turn back.

“This year my coworker and I have replaced countless boilers because of straight up corrosive water,” shares Vaiden. Both Bettis and Vaiden agree that it's better to treat scale than it is to replace corroded machinery.

Scale build up is expected, but Vaiden recounts a particularly notable experience. “The craziest scale I've seen was in a coffee brewer in New Jersey. The machine was overheating and when I pulled out the probe that reads the temperature, it was covered in the most beautiful scale I've ever seen. That brewer was filtered through a pretty heavy duty filtration system and still managed to accumulate probably the most scale I've seen at one time in my life. It was quite impressive.”

Most technicians have seen both sides of water damage, and agree it’s better to descale your machine than to try using very soft or distilled water. Along with soft water being corrosive, descaling your machine isn’t difficult. “When you run a descaling agent through a machine, it is slowly dissolving those particles,” Vaiden says. “When you flush the machine with clean water, the scale will come with it.”

“A descaler is an acid and you're using the acid to dissociate and basically neutralize the scale so that it enters the solution again,” Bettis adds.

Regularly descaling — Urnex recommends descaling once every three months — will help preserve the longevity of your machine. Not only will your machine thank you, but the process of descaling takes longer the more scale is built up.

If you’re intimidated by the process of descaling your machine, don’t worry. Urnex has a number of videos and tutorials for descaling your machine, along with a helpful guide on how to tell if you need to give your machine a quick clean, or if you need to descale. Descaling is a regular part of coffee maintenance, and once you see the process done, it’s easy to do on your own!