1.7 Estimating scaling rates in espresso machines (Water for coffee)
Description
This article is from the Water for coffee FAQ, by Jim Schulman with numerous contributions by others.
1.7 Estimating scaling rates in espresso machines (Water for coffee)
When a given lot of water has dropped enough scale to lower
its LI to zero, it doesn't scale any more. So scaling is not dependent
on how long an espresso machine is on or how much water it holds; it
depends solely on how much water goes through it (this is a slightly
conservative approximation, since the water may not completely descale
if it's at maximum temperature for only a short time).
So the scaling tables given above can be used to estimate the
amount of scale that your espresso machine is accumulating. The only
thing required is an estimate of the number of liters of water heated
to coffee and steaming temperatures going through your machine.
Multiply this figure with the amount of scale given for your water's
hardness and alkalinity, and you have the scale estimate.
In order to aid in this calculation, I have included a water
volume table for different types of drinks, as well as some examples.
LITERS PER MONTH FOR 1 DRINK PER DAY
--------------------------------------------------------------- Drink Espr+0 Espr+2 Espr+4 Espr+6 1CapSteam Americano Liters 1.80 3.60 5.40 7.20 0.61 3.60 ---------------------------------------------------------------
Some explanations:
The espresso + 2,4,6 refers to running ounces of water prior
to pulling the shot: on single boiler machines, to temperature surf;
on HX machines, to cool down the water or temper the head after idle
time. Use the figures appropriate to your practice. Commercial
estimates require knowing how often the baristas run water.
Sometimes espresso volumes go against the 125C table. On a
home machine cappa, the entire amount used for the espresso is
replaced in the boiler, then heated to steam temperature, thus the
usage creates 125C level scaling. If the boiler is never set to steam,
the 95C table should be used. On an HX machine, HX water used after
idling is at 125C; whereas "follow on" shots during high traffic are
at 95C.
Americanos pulled from water temp home boilers go to the 95C
table, those pulled directly from a steam boiler go to the 125C table.
Those made via a 2nd HX system go to the 125C table if there's been
idle time, otherwise to the 95C table. The Americano amount given is
additional to the espresso total.
If water scales at all at boiler temperature, the cappa
steaming volumes should be calculated at the lower of the water's
hardness or alkalinity figure, rather than the 125C figure, since all
minerals from the steamed water remain behind and scale out.
Some examples:
1. A Sylvia running 175 hardness, 125 alkalinity water is used
for 1 cappa, 1 americano, and 3 espressos daily. The temperature surf
is 4 ounces.
The cappa shot is on the 125C table: 5.4 * 92 /1000 = 0.50
The three espressos on the 95C one: 16.2 * 77 /1000 = 1.25
The americano also on the 95C one: 3.6 * 77 /1000 = 0.28
The steam use drops 125 mg 0.61*125 /1000 = 0.08
Total ... 2.11 grams per month
2. A coffee shop dual heat exchanger machine running 100
hardness, 50 alkalinity water (perfect coffee water) is used for 20
espressos, 400 milk drinks, and 80 Americanos per day. About 100
drinks are made after idle times and require 4 ounce HX flushes, the
rest are "follow on" shots without HX flushes. All the Americanos are
made with pauses in between.
Boiler scale: 400 drinks * .61 liters * 50 mg = 12.2
grams/month
Water HX scale 80 drinks * 3.6 liters * 17 mg = 4.9
grams/month
Espr HX scale 100 idlers * 5.4 liters * 17 mg = 9.2
grams/month
Espr HX scale 400 follows* 1.8 liters * 2 mg = 1.4
grams/month
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