This article is from the Water for coffee FAQ, by Jim Schulman with numerous contributions by others.
DESCALING SOLUTION Generally, a flush through descaler uses
about .5 to .75 fluid ounces (1 to 1.5 tablespoons, or 8 to 12 grams)
of citric or tartaric (grape) acid powder dissolved in 1 liter of
water. This is a 2.25% to 3.5% solution, equivalent to 33% to 50%
dilute lemon juice. Cleancaf and other coffee manufacturers' descalers
use this formula. Theoretically, these amounts will dissolve about 12
to 18 grams of scale per liter, but that would require leaving the
solution in for several days; in practice, it is used for an hour or
two to dissolve up to 5 grams of scale.
The formula is mild enough to be harmless to espresso machine
components, but it will come out of brass or copper machines with a
slight greenish tinge. This comes from milligram levels of dissolved
copper and is no cause for alarm.
5 lb bags of citric or tartaric acid cost about $10 at home
brewers' or soapmakers' supply stores. This is roughly a 20 year
DESCALING INTERVALS Know the hardness of the water you're
using, and how much you use the machine. Descale when accumulations
are between 2.5 and 5 grams. More often is a waste of time, less often
may result in scale build up. Check out section 1.7 for instructions
on determining your set up's scaling rate.
SINGLE BOILER MACHINES For single boiler machines, preventive
descaling is no problem, just follow the instructions given by the
manufacturer. In general, this involves filling the boiler, letting
the solution work for about ten minutes, and replacing it by running
it out of the steam wand under pump pressure. This procedure is
repeated three to five times, until about a liter of descaler is used
up. Then the machine is flushed with water until any taste is gone.
Manufacturer's recommendations differ on whether the brewhead
should be flushed or not. This is not surprising. The water's
temperature drops and LI rises as it moves from the boiler to the
head, so scale won't form there. In scaled machines however, fragments
can move from the boiler into the head, fouling the gicleur valve. My
guess is that with regular descaling, flushing the head is unnecessary
I do not know if the dual boiler Techno can be descaled in
this way, or if there is some procedure peculiar to it.
HEAT EXCHANGERS HX machines have two things to descale, the
boiler and the heat exchanger(s). Any descaling of a plumbed in
machine will involve moving the water inlet pipe to a tank that can
hold the solution.
Doing the heat exchanger is as easy as a single boiler
machine. Just run descaler through it until it exits the brewhead (or
HXed tap). Leave the descaler in for 5 to 10 minutes with the machine
off (or 2 to 4 with it on), then run out a 3/4 cup worth, repeat six
times until you've used up a liter of descaler. If the boiler refill
comes on during this period, very little harm is done, since it will
be adding only 20 ml or so to a liter or more of boiler water. Boiler
flushes (see below) can be scheduled after an HX descaling to minimize
this problem even further. However, ONLY USE CITRIC OR TARTARIC ACID
FOR HX MACHINE DESCALING, since if any remains in the boiler it's no
big deal, whereas smelly vinegar or cleancaf's detergent could be a
problem even at low concentrations.
HX MACHINE BOILERS Descaling the boiler is much more of a
headache. If you cook, you know that scale preferentially forms at the
waterline. This means that filling the boiler with descaling solution
only to the autofill line is not going to be very effective, since the
descaler will barely be in contact with the bulk of the scale.
Disconnecting the autofill (a wand like device sticking out of the top
of the boiler with a single wire attached) will fill the boiler to a
higher level and allow the descaler to work on this "rim".
In machines with a direct boiler tap, the boiler can be filled
by opening the water tap, and letting the autofill refill the boiler
with descaler. When that's done, close the tap, and disconnect the
autofill for 30 seconds or so to fill the boiler a little above the
regular water line. On machines without a direct boiler tap, the
autofill has to be disconnected, and the fill may have to proceed by
flushing the boiler through the steam wand. If there's an easily
accessible drain, it may be easier to use it in conjunction with the
If you're draining via the steam wand, don't let the machine
get too cold, otherwise the vacuum breaker will leak.
Disconnecting the autofill at the sensor risks shifting the
sensor's depth, so it's best to buy a spade lug and its mate, or an
inline switch that is rated for 130C ambient, and use them to make a
disconnect in the wire to the sensor. One can even extend the wiring
so this can be done without removing the case (i.e. so it's reachable
at the water tank).
Once the boiler is filled with descaler, leave it in for two
and half hours with the machine off, or one hour with the machine on.
The descaler is flushed out using the same procedure that
brought it in, either via the tap, steamwand or drain. Keep flushing
and refilling until there's no more lemon taste. This may take about
twice as much water as is usually in the boiler. It's best to refill
the boiler with RO water (see below). Add 5% to 10% tap water to keep
the autofill happy.