Manual Expobar Brewtus II (page 11 of 12) (English)

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Bella Barista

Nene Court, The Embankment,Wellingborough, Northants, NN8 1LD

Tel: 01933 273275

e-mail: claudettep@towability.com

Brew Water Temperature

The Expobar Brewtus II does not run hot as is usual with HX machines, which are a tight

compromise between continuously available steam, and production of brew water for

espresso. The twin boilers solve that problem, the brew water boiler running at around 101c

and the steam boiler at around 121c. The group is fed by the brew water boiler and has the

thermosyphon from there as well, so the group acts much like those on a single boiler

machine. There is no need for a big cooling flush because there is no water sitting in a heat

exchanger at 125c needing to be flushed out before the brew water is cool enough to make

espresso. The E61 group works well on this machine although you still need to flush!

I found that the brew water temperature rises as water is drawn from the group and at around

3 oz (90ml) reaches a plateau at a value similar to that displayed on the digital display (which

I had set to 95). This is for two reasons:

1. The water warms the group (so doesn’t get cooled down as much)

2. There will be some cooler water in the feed pipes to get rid of

This means that a 10-12 second flush would be recommended just prior to pulling a shot and

in practice I found this to give a shot that was not sour, or with too light a crema for the coffee

I was using.

This does beg a little more explanation of the Digital temperature controller. The digital

temperature controller is not a PID (proportional-integral-derivative controller). In many

respects the design of the machine makes it unimportant that this is not a PID (which is very

expensive). The idea of pre warming the water feed to the brew water boiler as it passes

through the steam/hot water boiler, is a great one and prevent those large variations of

temperature in the brew water boiler. The controller has an error of +/- 1c and the thermal lag

is only around 1c, so the temperature doesn’t vary much at all. e.g. if it’s set to 95 the heater

cuts in at 94 and brings it back to 95. This is unlike the 4 or 6 degree difference seen on many

other non heat exchanger prosumer espresso machines!

The temperature displayed is actually less than the actual boiler temperature and is meant to

reflect the temperature of the brew water. So at 95c the water in the boiler will be around 100c

(assuming of course the offset is at the factory default of -5c). The “offset” is what allows this

to happen; the “offset” is a preprogrammed value (which can be changed) of -5c and simply

means that the controller shows a temperature 5 degrees centigrade less than that actually

registered by the thermocouple in the boiler. So 100c in the boiler becomes 95c on the

display. This allows for the fact that by the time the water passes down the pipe and into the

“cooler” E61 group it will chill down by around 5c when it hits the coffee in the portafilter

basket.

It would be tempting to increase the “offset”, having the brew water hotter, the group warmer

and a smaller cooling flush (you may also find it advised to increase the offset on the web).

This is probably not desirable for a number of reasons:

1. Your running the brew water boiler hotter than you need to (all for the sake of pulling

30cc less on the “warming” flush)

2. If you pull more than one shot, or flush too long brew water may get hotter than you

expect (with the correct offset even if you flush longer or pull a number of shots

in a row, the temperature stabilizes at the expected value). With a larger offset

although the temperature will achieve the desired value, flush for too long (or pull

more than one shot and it could exceed it.

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Expobar Brewtus II Manual

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