Consistency Part 1

Exploring the consistency of the Breville Oracle Touch grinder and tamp fan.

While brewing daily with the Oracle Touch, I have observed some inconsistencies with my espresso shots, even after dialing-in and pulling several nice shots in a row. In an effort to isolate the source of these inconsistencies, I wanted to run a series of tests with the Machine. This first experiment focused on the grinder and tampfan side of the Breville Oracle Touch machine (Part 1). Part 2 will focus on the group head, specifically looking at channeling using the Breville bottomless portafilter, part 3 will look at grinder retention and single-dosing, and part 4 will review all three experiments to see what we can learn and how we can improve our consistency with the Breville Oracle Touch machine.

For this experiment, I used a medium roast coffee, and brewed at 200 degrees Fahrenheit and with a timeout of 28s. I used the Breville Double Spouted portafilter and the original double basket. The machine was already dialed-in for this bean before the experiment. For consistency, I made sure to refill the hopper every two shots to maintain the same weight pushing down on the burrs. For every shot pulled (10 total), I ground the beans and then weighed the dose, then brewed the espresso with a timeout of 28s. Upon completion of the shot, I weighed the yield and recorded the following data:


































Before we jump into the data, I want to emphasize that these results are from my machine, from a single afternoon of testing, so not really enough to draw definitive conclusions. Also, my results may vary from how your machine performs, for better or worse. As we look at the data, keep in mind that the machine was on, and in use for about twenty minutes before I started the test. So, this is not from a cold start. And lastly, during the test I made no adjustments to grind settings, or anything else on the machine.

First, looking at the dose data only, the green line represents my target dose of 20g, which is where I’ve tried to calibrate my tamp fan to… but with this machine, adjusting the tamp fan is definitely a trial and error process.

We can see that the first and sixth doses (depicted in green) were right on target, and the second through fifth doses (depicted in yellow) were within acceptable range. After that, dosage started to trend upwards, with two doses being too far out of tolerance to be able to pull a good shot at that grind setting, and the last shot, coming in at 20.3, probably right on the edge of acceptable. So eight doses out of 10 were close enough to my target dose. This is actually better than I expected.

The issue here is not the little bit of extra coffee in the dose, but the fact that if you are expecting exactly 20g, you will not understand why your yield is fluctuating so significantly. For these two doses in red, you will see on the next graph that just this amount of extra coffee will reduce your yield significantly.

The other interesting observation is that the dose was pretty steady for the first six shots, and after that started to trend upwards significantly. I am puzzled about why that might be. If you have ideas, please add them to the comments below. I am wondering if the burrs begin to shift as the machine gets warmer and warmer? Or perhaps the beans behave differently when they are ground up as they get warmer and warmer from sitting on the burrs and in the hopper? On the bright side, I imagine that most users of this machine are not pulling more than six consecutive shots in one sitting. With our use, we pull four shots every morning and sometimes a couple more in the afternoon, but never this many in a row.

Now, looking at the yield data only, the green line depicts my target yield of 40g at a timeout of 28s. You can see that the first four shots are right on, or pretty close to target, leading me to think that I’ve dialed-in the machine pretty well. Shot #3 maybe had some channeling, but it’s hard to say… we’ll explore channeling in the next video and article. But starting with the 6th shot, yield started to trend downward significantly.

I think that there are three significant observation from the above graph:

1. Shot #6 is most telling, because this one dosed right at 20g, yet the yield was well below the previous five shots, which were all also close to 20g. I think that this is an indication of the burrs indeed shifting closer, and thus delivering a finer grind. As you can see, all the subsequent shots brewed lower yields. So in this case, if you are brewing with a scale, you would notice this and shift your grind setting coarser by one or two steps, and you would be back on track.

2. The second interesting observation is that the two lowest yields, so the two reversed peaks on graph 2, match the two peaks of highest dose on graph 1. This shows that stray doses will definitely ruin shots. So if you are seeing some puzzling yields, either too much or too little espresso, it is more than likely from an over or under dosing from the tamp fan.

3. The last takeaway from this graph is the importance of brewing with a scale. If you are brewing with a higher timeout than the 28s that I set for this test, you would be able to stop the first four shots right at 40g, probably still very close to 28s, then you may be able to salvage the 6th, 8th, and 10th shots by brewing for 30s, or perhaps 31s. Brewing with a scale will also show you that something is going wrong, and you can adjust your grind coarser, and maybe not even skip a beat. If you are brewing without a scale, you can see that you could brew five pretty good shots, and five bad shots, and not really understand why. If you are drinking a latte, you may not taste the difference between the pretty good shots, but you will definitely taste the bad shots. If you are drinking espressos, cappuccinos, and maybe even americanos, you will be able to tell the difference between a great shot with adequate brew ratio, an average shot that comes close, and a bad shot.


The big takeways from this experiment are:

1. Stray doses do happen, I am sure of this now. I suspected this was the case, and the data confirms this. Random bad shots are more than likely caused by a higher than anticipated “stray” dose from the tamp fan.

2. It confirms my experience that sometimes I have to adjust my grind settings in the middle of a brewing session, even after brewing a few great shots. I believe that his may be due to heat on the burrs and/or on the beans. The Oracle Touch machine makes adjusting the grind settings really easy, so this is no big deal, but I do wonder if the all-in-one design, and potentially the heat transferred to the conical burrs and/or the beans is a significant drawback of this machine.

3. Lastly, if you are not brewing with a scale and wondering why you are brewing bad shots, I can’t recommend enough buying a simple scale like the one below for just $12. It is likely the single greatest improvement you can make to your espresso brewing, besides buying quality fresh coffee.

Watch the video!


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