I need to descale my espresso machine. What’s next?

Well, first, and most importantly it depends on the type of espresso machine you have.

This article will focus on home espresso machines. Commercial espresso machines (or machines that are plumbed in) never need descaling. We know that you are using filtered water and are keeping up with filter changes, so the chances that something else will fail on the machine is greater than an issue caused by scaling. For more information on water filtration click here.

If your espresso machine has a screen that displays a message that says something like “Descale Now”, then it is perfectly fine to do what it ask. Consult your machine user manual for the proper descaling procedure

Liquid Espresso Machine Descaler

In general, there are several different types of espresso machines that exist. They operate on the same premise that a quality espresso shot is dispensed at 9 bars of pressure (130.5psi). The difference, when it comes to descaling, lies in how the hot water is created and how it is dispensed internally.

TypeImageDescriptionBoiler SizeDescale?
Fully-Automatic (Super Auto)The water in this style machine is typically heated on demand. This means that the cold inlet water is routed through a heated metal block that has a maze style path with a diameter roughly the size of a sewing needle. You could imagine how quickly bad water could clog these up! These machines will need to be descaled and usually will display a message when it is time to descale.On-Demand
Pro-SumerNormally, purified drinking water is put in a reservoir tank and when the machine calls for water, it is gravity fed to the pump and dispensing commences. If the steam boiler calls for water, it will continually fill the boiler until it reaches a certain level and is satisfied. Whether a single or double boiler, these machines do NOT need to be descaled. If you would like to read our humble opinion on why this is, then read on. ~ 1 liter
Semi-AutomaticSimilar to a pro-sumer espresso machine, water is added into a reservoir tank and is pulled out of the tank when the user activates the pump. One of the main differences in these machines vs the pro-sumer machines is that these require the user to manually fill the boil for proper use. The pro-sumer machines will keep the steam boiler full automatically. In this style machine, usually the steam boiler shares the same space as the hot water boiler. In the pro-sumer machines, there is usually a heat exchanger in the steam tank to heat the group head dispensing water.
These machines can usually be descaled without any issues, but feel free to read our humble opinion on why these probably do not need a descaling.
~ 1 cup
ManualThese fun machines accept a pour of water directly into the boiler. By unscrewing the cap to put water in, you can actually inspect the heating element to see if there is scale building up. The best thing about these is that usually there are no small orifices to get clogged up, so these can take some serious usage before descaling is needed.~ 4 cupsMaybe? Ok, NO.

Our humble opinion on why you should never descale your espresso machine (unless it ask you to).

A descaling procedure involves putting acid (most commonly citric acid) in the water supply reservoir and filling the boiler. This means that your pump is ready to go through a work out and your machine is going to hate you.

There are at least 3 problems that arise when you do this.

  • the descaling solution does its job and dislodges chunks of particulate that is then sent downstream in efforts to be pushed out of the tiny group head or hot water wand orifices. This one speaks for itself.
  • the acid solution is corrosive and wears things like gaskets and o-rings.
  • secondly it takes forever to actually flush your boiler out after you have filled it with acid.
  • keep in mind that most pro-sumer espresso machines utilize a heat exhanger inside the steam boiler. So, if your steam boiler is already full of water, then you would just be pushing descaling solution through the heat exchanger and out the group head.

    Still Interested? Keep reading.

Let’s keep things simple and assume that the magic number is 1.
– The espresso machine boiler takes about 1 L of water.
– A powdered descaling solution packet of 30 grams is mixed properly with 1 liter of water – The main pump will operate at 1 liter per minute (1 L/min).

Let’s assume you have Pro-Sumer style machine.

The instructions would probably say to fill your water tank reservoir with the said 1 liter of acid solution and pump all of it through until empty. Let it set a while. Fill water tank reservoir with 1 liter of clean water. Flush.

Bring in the Math. Please be warned this is not for critical application and is just for fun. We have been known to make errors in our collegiate exams, rendering pages and pages of calculations useless. Whoa!!

In a few ways, this is a perfect scenario of a Differential Equations mixing tank problem. Let’s see how long it takes to completely flush out the boiler that is full of descaling solution

Note: For the math below, we are going to skip the step of pre-mixing the acid solution in the water reservoir with the current water contents of the boiler.
We will do that math in a little bit to see what amount of acid is actually in there to start when adding descaling solution to a boiler already full of water. For this math experiment, we are just going to assume that the boiler is empty and we just filled it with 1L of our descaling solution. In our case, it was 1 liter of water mixed with one 30g powdered descaling packet.

How to find the amount of solution A (acid) in the tank at any time, and after a specific amount of time has passed.

We will start with the mixing problem formula (da/dt​​=C​1​​r​1​​−C​2​​r​2​​) and just plug things in.

C1 = 0 kg/L since no acid is being added to the boiler. We are flushing it out with clean water.
r1 = 1L/min is the rate at which our clean water is flowing into the boiler to flush it out.
C2 = a/(1+t) kg/L because we do not know how much acid is leaving the tank, but we know how much acid solution we started with.
r2 = 1L/min because the water leaves the boiler at the same rate the machine is pumping.

After this math, the differential equation is simplified to:

a = C/1+t

So if we have:

C = .03kg because that is how much acid powder we had in our packet.
t = 1… for one minute.
a = .015kg or 1.5 grams.

This math works out. In 1 minute of pumping, the acidic descaling solution concentration is cut in half. This also means that if we went with one 30g packet of descaling powder mixed in 1 L of water and then added this to an already full boiler of water, we would end up with half of the concentration of the original acidic descaling solution. Is it being effective at all at this point? Probably not.

What happens if we let the pump run continuously for say 5 minutes pumping fresh water (that’s 5 liters) in the boiler in order to get rid of the acidic descaling solution. How much acid powder still remains?

C= .03kg because that is how much acid powder we had in our packet.
t = 5 … for 5 minutes
a = .005 or .5 grams.

So after stressing the pump out by running 5 liters of water through the machine, you still have a 1 liter boiler with water that has .5 grams of acid in it. How does your shot taste?