Hey guys,

I've got a Breville Dual Boiler 920, and I've started to doubt the accuracy of its displayed temperature. I think that my machine has started putting out water that is several degrees colder than it states. Without changing any parameters with coffees I've had dialed in for months now, shots have started to taste more and more sour over the last couple of weeks. For instance, a coffee I'd normally extract at 200 F will now have more of an acidic taste than it used to, unless I bump the temperature up to 202 or 203F.

This has been consistent across three different types of beans.

Has anyone else had anything like this happen with their machine? Is this an easy fix? Or does anyone have any tips on how I can correct this?
Or is there an easy way to verify the accuracy of the temperature?

I've tried using my thermapen Mk4 to measure the temperature of water coming out of the showerscreen directly, and it's been consistently about 7F colder than the machine states. But this is obviously not a very precise way of measuring temperature, and I have no idea whether that much heat loss would be accurate anyways.

Any tips or suggestions would be appreciated.

Thank you

I agree that measuring it like this is wildly inaccurate, but I have a thermapen handy so I can at least give you a sanity check. I ran a 30s empty portafilter extraction into a cup, let it sit for 30s to warm up the cup, then dumped it and ran another 30s shot. My machine is currently set for 199F and the second shot measured 189.9 F, so roughly a 9 degree difference.

Edit to add that the ambient temp is currently 70F outdoors and 74F indoors.

Thank you! Setting mine at 201 and doing the exact same method as you, my second shot was about 186 F, so a good 15 degrees difference by the time it hits the cup. And it's about 74F indoors.

Maybe my taste buds are just changing and nothing is wrong with my machine at all, but this does make me think something is off on the machine side.

Ideally, you'd measure with a Scace device. Short of that, you can probably jam a thermocouple into the portafilter to get a more accurate reading - or at least collect the water in a low heat capacity vessel (metal or plastic cup).

I think the BDB measures temperature at the boiler, so you wouldn't expect grouphead temp to match the readout unless there's an offset to compensate.

NoStream wrote:I think the BDB measures temperature at the boiler, so you wouldn't expect grouphead temp to match the readout unless there's an offset to compensate.

Besides having a PID for both the steam boiler and the brew boiler, the BDB also has a PID for the group head to control the temp, which is heated independently of the boilers by means of a heating element inside the group head.

Could it be the beans aging? Are you redialing them in as they age? How fresh are they/how long do you keep them? Also have you checked with the roaster to see if any changes have been made in the roast? I know sometimes roasters have to change components of a blend during different seasons.

Not trying to say there isn't an issue with the machine just giving you something else to consider.

Also how old is your grinder? If it was a new grinder you may have put enough through it to season the burrs and might need a finer grind.

Just giving some other possible ideas to think about before you start taking apart the machine or send it to breville for repairs.

Definitely appreciate it.

The beans are all fresh from the roaster within a week, and a pound never lasts for more than a week, so I've ruled out freshness.
The grinder is 9 months old now. I've added a shim to it once, but it's not an issue of how fine the coffee is either in this case. The shots are pulling in the correct time frame, and so long as I increase the temperature a couple of degrees, there is no issue.

I'm beginning to wonder if it has something to do with the fact that I'm in Calgary. I was living in Portland until a month ago, and now I'm at a much higher elevation, and the water is generally much harder here. But from my understanding water being too soft could lead to sour coffee, not hard water.

https://en.wikipedia.org/wiki/High-altitude_cooking

Hafta noodle on the effect of this relative to the BDB.

It could be the elevation itself. I remember reading a few threads about the difficulty of high elevation brewing. I don't know if Calgary's 3500' qualifies as high, but it's certainly different than Portland.

Yeah I say "high" relative to Portland haha. Although funnily enough, that difference was absolutely killer my first week back. I'm a runner and I was certainly noticing the lower oxygen.

In any case, I'm just going to elevate the temp a bit and overfill the portafilter to bring out some more bitter notes until I can figure this out. For most beans this works. It's with my Malabar Gold I'm getting pissy, even at 205 on the BDB it's coming through without any sweetness, and when I was in Portland using MG, it was like drinking chocolate.