# What Bar is best?



## Filthy_rich85 (Jan 20, 2011)

Hi coffee geek

The magic number is actually 9 bar but that's out of the group head. The 15/19 bar manufacturers refer to is the pressure produced from the boiler. If you're looking go a new machine I would recommend enquiring about pressure achieved in the group head rather than the boiler. Some machines such as the Silvia can be tweaked to ensure the 9 bar is achieved


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## jimbow (Oct 13, 2011)

I think the 15/19 bar is actually what is coming out of the pump. In most domestic machines this will be a vibe pump which means that it is typically producing up to 15 bar of pressure. To compensate for the fluctuation in pressure with vibe pumps, these machines typically have an Over Pressure Valve to stop the pressure at the group head exceeding 9 bar.

Higher end machines with a steam boiler do indeed have pressure build up within the boiler but this is usually to 1 to 1.5 bar.


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## jimbow (Oct 13, 2011)

Trying not to open a whole can of worms here, but 92 degrees C is a fairly typical target temperature for brew water. Some people will like higher temperatures and some lower and some will say that the target temperature will depend upon the coffee. SquareMile coffee will recommend temperatures for different coffees they roast and sell.

Most domestic machines use a thermostat on the brew boiler to control the heating element. Precise control of the brew temperature with a thermostat is not really possible and the best that can really be hoped for is a consistent temperature from one shot to the next. These thermostats often tend to have quite a large dead band (the swing in temperature between where the element is activated at the bottom, cold end to where it is deactivated at the top, hot end). This swing can sometimes be as much as 10 degrees (perhaps 5 degrees either side of the target temperature). This is why many people employ a trick known as "temperature surfing" to return the boiler to a known, consistent temperature immediately before brewing the espresso.

To temperature surf, simply run brew water through the group head without the portafiler engaged. This draws cold water from the tank into the boiler, lowering the overall temperature of the water in the boiler. The amount of water to draw through will depend upon the size of the boiler but draw water at least until the temperature is low enough that the heating element comes on (there should be an indicator bulb for the heating element or perhaps a "ready to brew" light - in which case, this will go off at this point rather than come on). Once the light has come on (or gone off depending upon whether the bulb indicates that the element is on or that the boiler is up to temperature and ready to brew respectively), wait for the bulb to switch off (or on depending upon...). This means that the water in the boiler is now at the top of the thermostat's temperature band. Some people like to brew as soon as the boiler is at the top of band, other's like to wait a pre-determined number of seconds for the temperature to fall to an ideal temperature.

As an alternative, some people fit something called a PID to their machines which gives highly accurate temperature control to within a degree. These also come as standard on some higher end double and single boiler machines.


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## MikeHag (Mar 13, 2011)

66C is too low by far to brew espresso, so either it is malfunctioning or whatever means your using to measure the brew water temperature isn't accurate. I'm guessing the latter, cos if it was the former then you'd know from the horrible espresso it made. How are you measuring?


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## Glenn (Jun 14, 2008)

Where are you measuring the temperature, and are you using a Fluke or similar probe fit for purpose?

Are you measuring up through the portafilter or with the shower screen exposed?

66c sounds far too low


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## MikeHag (Mar 13, 2011)

Let's see who gets in first...









Unfortunately measuring the water coming out at the brew head is not that simple. The water will have lost a surprising amount of heat between the machine and the cup ... 66 isn't all that unusual in the cup (maybe a bit low) but you'll need to take more detailed steps to get something approaching accurate. I bought a cheap digital thermometer with k type thermocouple wire that I run over the top of a blind basket during backflushing. Maybe you could try similar, but during brewing rather than backflushing (since backflush prob isnt an option on your machine)


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## jimbow (Oct 13, 2011)

The water tends to loose a lot of heat as it falls into the cup. There is a polystyrene cup method that tends to give a more accurate representation of the brew temperature at the group head. Have a search on the forum or google but it basically involves sticking a probe thermometer through a polystyrene cup and then jamming the cup into the group head to prevent heat loss.


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## jimbow (Oct 13, 2011)

MikeHag said:


> Let's see who gets in first...


Beat me!


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