Just wondering what the general consensus is on something as simple as this, with the BDB. I know it's not an HX machine, but do most users flush a little (or a lot) of water immediately before inserting the portafilter and brewing on this machine?

The only thing I've noticed in my own experience is that there is sometimes a second or two delay before visible flow of water, if I haven't flushed just before the shot.

Just looking for insight/experiences!

Same delay on my bdb. I've got the the single shot programmed for a 4 second pre shot flush and the double shot button for a 7 second post shot flush to get the group head clean.

Excellent idea!

Also a very good suggestion!

GregoryJ wrote:I only tend to run water if I just changed the temperature. Because when I change 1 or 2 degrees F, it reads the new temperature immediately. I am a little suspicious, so I run some water to try and force it to seek out the new temperature.

I think the boiler is NOT kept at the temperature you set in the window. It's some amount cooler than that. The final heating is done in the group head where there is a second PID heater. So if you drop the temp by a few degrees or raise it by a few the group heater will run more or less to provide the final selected temperature, if you were to run a Scace test.

-Peter

Whew, this ended up being a wall of text so I'll start by saying that flushing shots can help... sometimes.

Between the auto-on setting and a fairly consistent morning schedule, my machine is usually fully warmed and temperature stable by the time I want to pull a shot. I use really short flush shots afterwards to help clean out the residual grinds and oil as part of my cleanup routine. Later in the day my shots are more adhoc and I'm starting from idle temperatures. In this case I use flush shots to help bring the portafilter (and other parts) back to temperature more quickly. I find I can get the machine to 'good enough' in 3-5 minutes or fully temperature stable under 10 minutes using this method.

Like some of you noted, the temperature readout is a little suspicious because if you watch it climb while warming up it'll jump several degrees to the target temperature at the very end. The same tends to happen when adjusting the temperature settings, showing that it's instantly at the new target temperature. I suspect the BDB allows for as much as +/- 5 degrees F variability, which is a shocking large window. The heated grouphead is an integral part of the BDB design and helps drive the final temperature. Unfortunately, I don't think it fully compensates at the extremes of the allowable temperature window. This is most noticeable on startup; try this as an experiment:

1. Wake the BDB from idle and wait until the temperature display locks in at your target temperature. Pull a shot and take note of how it tastes.
2. Wait another 5-10 minutes for the boiler temperature to stabilize. Pull another shot and note how it tastes compared to the first shot.

Both shots are pulled when the machine says it's ready, but I bet you they taste different. My morning shots are similar to #2 and always super consistent. The adhoc shots later in the day are more like #1, sometimes great and sometimes less so depending on how long I waited on the warm-up. Eventually I found that I pull adhoc shots closer to #2 without having to wait so long by forcing all the parts to warm up with flushing shots.

The issues with getting to to the initial temperature come down to the boiler design trade-off between time and accuracy. The boiler runs at full throttle at the beginning, but as the water gets closer to the target temperature it needs to dial back so it doesn't overshoot the target. A wider temperature window means the machine can be more aggressive with the heating and still end up somewhere in the window. I think because of the target consumer market, Breville opted to keep the startup time lower because most people won't notice the difference anyways.

Do you need to flush between shots like on an HX? No. The machine is very temperature stable overall. Once the machine is at temp, the grouphead does a fantastic job keeping it locked in. It's honestly one of the better features of our machine.

Interesting theory. Might bode some testing. We already know it's a Scace test killer (Phil said it was literally designed using Scace devices, for this purpose).

BUT now that you have presented an anecdotal situation based on your testing, we should try to get some numbers. Not many ordinary users have a Scace device, but unless you are making comparisons to other machines, you do not necessarily need one. One of the guys in a small private group I am in, almost has a "poor man's" Scace made up of one of the stock Breville pressurized baskets and a silicone disc with a hole in the middle. Get a k-type thermocouple in there and you have essentially a Scace (though you can't compare numbers with an actual one). This would be enough to test the theory present above.

Here's something you guys might find interesting... I have my BDB plumbed and running an external rotary pump (under the kitchen sink). Well, without a puck, the rotary can wail out some water. On the order of 3x the flow rate of the stock vibe pump if I open my needle valve all the way, (see the BDB Slayer shots thread). Well, if I run it full throttle long enough, the display will start to flash because I would have evacuated enough of the stable water in the brew boiler that the cold water coming in quickly drops it out of spec for a few seconds. This experiment is of no practical value because you would never do it to make espresso. Just an observation.

By the way, this reminds me of something that current GS/3 MP users are discovering with the current conical valve design. As with the water tap pressure dump you can do with the stock BDB, the conical valve GS/3 dumps the excess water overboard into the drip tray. And it really fills it fast if you are doing a long pre infusion because you like light roasts. Lots of water waste. But that's not the point. What happens during large water wasting events is you get large boiler fills too... enough apparently to drop the boiler temp by a few degrees. Not what you normally expect in a saturated brew group design.

BTW I programmed a button for a seven second flush at line pressure (my BDB is plumbed), mostly to warm the cup.

-Peter

pcrussell50 wrote:... a "poor man's" Scace made up of one of the stock Breville pressurized baskets and a silicone disc with a hole in the middle. Get a k-type thermocouple in there and you have essentially a Scace (though you can't compare numbers with an actual one). This would be enough to test the theory present above.

I'll read up on how the Scace works and see if I can build a knock-off to test with. I don't mind sacrificing a pressurized basket or two.

Short version of Scace: it mimics a puck by allowing pressure to build to about 9bar while flowing about 1.5ml/s which is a typical flow rate. Give or take.

In order to test your theory, you don't need identicality with Scace. However if you build something that close to a Scace, then who needs to buy one

-Peter