Nuova Simonelli Oscar II - starts dripping too late - Page 2

Need help with equipment usage or want to share your latest discovery?
Beezer
Posts: 1355
Joined: 17 years ago

#11: Post by Beezer »

I don't think anyone's asked yet, so I'll do it. What kind of coffee and grinder are you using? 90% of the time, these kind of problems are caused by either stale coffee or a cheap grinder, or both.

That said, the variations in volume of water when there's no PF in the group don't make any sense to me. I don't know the Oscar II, but I thought most volumetric machines use a flowmeter, so if there's no flow restriction from a coffee puck, the amount of water for a given time should be the same every time. If you're getting large variations in flow when there's no PF in the group, there might be a problem with the automatic dosing system.
Lock and load!

User avatar
bluesman
Posts: 1594
Joined: 10 years ago

#12: Post by bluesman »

Beezer wrote:90% of the time, these kind of problems are caused by either stale coffee or a cheap grinder, or both.
bluesman wrote:Again, this kind of variance in shot times & volumes is most often the result of poor or inconsistent grinding, dosing, distributing and/or tamping.
Yes indeed - problems with shot times and volumes are almost always somewhere in the portafilter basket. The hooker here is the reported variance in unrestricted volume flow, which I simply don't understand and can't explain.
Beezer wrote:most volumetric machines use a flowmeter, so if there's no flow restriction from a coffee puck, the amount of water for a given time should be the same every time. If you're getting large variations in flow when there's no PF in the group, there might be a problem with the automatic dosing system.
The amount of coffee produced should be as consistent as the amount of water pumped into the PF for a true volumetric machine - there's nowhere else for the water to go but out the bottom of the PF (except for the tiny amount retained in the puck, which should also be very consistent with the same coffee, dose, grind, and tamp).

The term "volumetric" is used in some places to describe Oscar II. But I just reread all the NS literature on Oscar II, and there's nothing in the parts list or electrical diagram to suggest that it has a flowmeter or any other internal volume measurement capability. It looks to me like the buttons are variable timers that you "program" by watching or measuring what goes into the cup. As you suggest, true volumetric dosing requires measuring the volume of water that's pumped into the PF, not the volume &/or weight of the espresso coming out - and Oscar II doesn't seem to have this capability.

deusdeorum (original poster)
Posts: 10
Joined: 8 years ago

#13: Post by deusdeorum (original poster) »

bluesman wrote:It might be instructive to build a PF / pressure gauge with a variable orifice in the bottom
I was going to build a system with a faucet to be able to adjust the flow, and test it with variable resistance. Something like this.
Beezer wrote:What kind of coffee and grinder are you using?
I use relatively expensive coffee from the local coffee house, which they use for making coffee there. As for today, it was roasted 9 days ago, but I've never used coffee older than 2 weeks. The grinder is Mazzer Super Jolly Manual, and grinding fineness seems consistent to my newbie eye, but when I was buying it (used), I had my barista friend with me. And I haven't changed any settings for a couple days, during all these tests.
bluesman wrote:and there's nothing in the parts list or electrical diagram to suggest that it has a flowmeter or any other internal volume measurement capability
Yes, the buttons are programmed to fixed time. I set 28 seconds for the double button and haven't changed it.

So I've made the video. A little later, I'll show you my espresso volume/time test.
Here in the video, the sequence is the following: 20mins preheating - flush - flush - flush - 10 mins idle - flush - 20 mins idle - flush - flush
The results, as you can see, are: 265g, 198g, 193g, 191g, 188g, 196g
Seems quite consistent after the first run, but the pattern is the same: it gives more after no flush, and less after flush, it will be more clear with espresso.

deusdeorum (original poster)
Posts: 10
Joined: 8 years ago

#14: Post by deusdeorum (original poster) »

so! I built a pressure gauge for my portafilter

Then I adjusted the needle valve for the pressure to be 10bar, and did this test repeatedly:
1) Run it without portafilter
2) Run it with portafilter with pressure gauge
3) Run it with portafilter with pressure gauge
4) Run it with portafilter with pressure gauge

And all the times I ran it I got the same result:
1) When I run it after flush (running without portafilter) the pressure goes to 10 bar in 19 seconds
2) When I run it again the pressure goes to 10 bar in 5 seconds
3) If I run again - same 5 seconds

It's very consistent. I did it many times.

It's the same pattern as with "dripping start" with my espresso. If I flush, the required pressure is achieved in a very long time (19 seconds).
So to make espresso I need to make another espresso and pour it out.
Is this the expected behaviour? If not - can I fix it myself? If not - what should I tell to the NS support?

seekjim20
Posts: 5
Joined: 8 years ago

#15: Post by seekjim20 »

I also bought a Oscar II a few months ago. I have exactly the same experience as you do. Here is what I understand from experience and conversation with NS support.

(1) You do need to flush it before making espressos. For two reasons. One, the water in the pipe after the machine is warmed up (20-30 mins) is overheated; two, it is also "stale" water that have been left in the pipe for a long time, compared with the fresh water in the tank. So it is not good for your espresso.

(2) The machine is supposed to run with back pressure. For unrestricted flow, the machine doesn't consistently put out the same amount of water in the same amount of time. The support person in NS told me so when I asked. I'm not sure the reason, but it doesn't seem to affect the espresso shot, see below.

(3) Before each shot, I flush the machine until the water coming out of the screen doesn't have that hissing sound, which indicates flash boiling, plus a few more seconds. Then I put the portafilter back in, loaded with 16 g coffee, distributed, tamped. When you hit the start button, the machine slowly ramps up the pressure. At around 3 sec, you'll hear a click, which is the first time water starts coming out of the shower screen. If you have a bottomless portafilter (I do), you'll see some liquid just starting to come out from the bottom of the basket. At around 15 sec, espresso starts to really come out. I usually aim for the total time counting from that 3 sec to the end of the shot to be 30 sec, 30 g in weight. The exact time depends on personal taste, but what I found is if you weigh your input, and distribute and tamp properly, the output is usually pretty consistent, to be within +-1 g.

I feel that this late dripping is similar to the pre-infusion function in other heat exchange machines. Although for some reason, when I asked the tech support from NS, he hesitated to agree.

I really like the machine, now that I've become used to it. My favorite is to watch that two streams of dark, viscous liquid coming out of the spouts of the portafilter. My suggestion will be: give it some time, and start with the manual control (overwrite the program), so that you can have the chance to salvage a not so good shot. After a few weeks, when you get the hang of the machine, you can start doing automatic shot.

Good luck. Enjoy your espresso.

deusdeorum (original poster)
Posts: 10
Joined: 8 years ago

#16: Post by deusdeorum (original poster) »

I do agree, that it is possible to make a good coffee, and to get used to live with it.
But still it seems to be a problem for me.
If you aim to 30sec, and the pressure raises after 15sec, then it's more likely to be 15 second shot with 15 second preinfusion, as for me. And so the fineness should be coarser, if you really get the desired volume. But if you get your best espresso - then no questions.
I get my best espresso with the 2nd cup, made just after I waste the first one, without a flush in between.

I googled a bit, and found multiple topics about dwell time delay for Oscar I, but no clear reason or a clear fix for this.
It was sometimes 3-way valve, sometimes retention valve (?) and sometimes OPV (which i don't have).

User avatar
Bob_McBob
Posts: 2324
Joined: 15 years ago

#17: Post by Bob_McBob »

The reason it takes so long for the pressure to climb the first time is because all the recesses of your portafilter and gauge have to fill with water first. On the subsequent measurements it is already full and thus rises immediately.
Chris

deusdeorum (original poster)
Posts: 10
Joined: 8 years ago

#18: Post by deusdeorum (original poster) replying to Bob_McBob »

Probably I did this mistake while doing the experiment. But this cannot be applied when I'm doing a series of espressos. I detach the portafilter, clean it, put new coffee inside, but still the time is short, if I don't do a cooling flush before.

andreugv1
Posts: 65
Joined: 8 years ago

#19: Post by andreugv1 replying to deusdeorum »

Did you ever solved it? I recently bought a NS Oscar II and fill like I am in the same problem as you.

deusdeorum (original poster)
Posts: 10
Joined: 8 years ago

#20: Post by deusdeorum (original poster) »

andreugv1 wrote:Did you ever solved it?
I can't say I solved it, but I found a workaround. Before each cup (after the cooling flush) I turn on the pipe for <3 seconds (before the click sound) 3 or 4 times. I can tell, that the pressure is fine by the sound (it becomes quiet). And by doing this I have necessary consistency every time.