Choosing an optimal Brew Pressure

[kav]

On my Anita HX machine, I initially worked with a max brew pressure of 9.2 bar. I found that I got nice, round, sweet flavors out of most coffees. But I didn't get the full spicy complexity out of some blends (like Artigiano's) like I was tasting in the shops, so I raised my pressure to 9.5 (which many people have recommended). I'm now finding more interesting spices in my shots, but also increased sharpness in the acidity and astringency -- and less round, pleasing cocoa flavors and sweetness.

Optimum pressure seems to vary from blend to blend, but this information is rarely discussed when people are reviewing blends. And changing pressure on most machines is somewhat of a pain to do.

How do others who have explored this extraction space handle this issue when going from blend to blend? How do top cafes handle this, assuming they don't have such fine pressure control as the Synesso or GS3?

[AndyS]

How do others who have explored this extraction space handle this issue when going from blend to blend? How do top cafes handle this, assuming they don't have such fine pressure control as the Synesso or GS3?

The GS3 doesn't have "fine" pressure control. Like most other rotary pump machines, it uses the pump's built-in bypass valve to regulate brew pressure. The right hand gauge in photo measures the brew boiler pressure; as brew water flows through the gicleur, there's a pressure drop of about 0.15 bar (the exact pressure drop depends on flow rate). Net effect is that the brew pressure at the puck is about 0.1 - 0.2 bar less than the pressure indicated on the gauge.

I don't know the details of the Synesso, but I believe it just uses the rotary bypass valve, too. Anyone?

[kav]

Are there any tips for the home barista, like how to find that optimal single setting?

Thanks,
Mike

[shadowfax]

Are there any tips for the home barista, like how to find that optimal single setting?

you could just set it at whichever pressure you like and then only buy blends that perform well at that setting.

I suppose you're "limiting your experience" by doing this, but if you don't want to reset your OPV every time you change blends, I don't see a lot of other options, other than variation you could get in brew pressure by varying grind and tamp, at the expense of varying the flow rate and volume of your shots...

[kav]

Ah, so some people really are modifying pressures per blend? If so, is that based on personal experience only, or are people sharing ideal pressures as well as ideal temps per blend? Just trying to understand if there's an opportunity here for us to do something to improve the experience.

[krus]

Kav, what is happening is when you adjust your expansion valve to increase or decrease the brew pressure you are changing the brew temp along with the pressure. A change in flow rate will change the brew temperature. I've found through trial and error that I achieve the best extraction around 9 bars. You'll get less pitting, while still producing rich shots with plenty of crema.

[RapidCoffee]

Kav, what is happening is when you adjust your expansion valve to increase or decrease the brew pressure you are changing the brew temp along with the pressure. A change in flow rate will change the brew temperature.

Maybe I'm missing something, but it seems that this effect would be indirect at best. The OPV sets the max brew pressure, not the temp. To change the brew temp, adjust the boiler pressure via the pressurestat (higher pressure => higher temp). Or play with the HX cooling flush (more idle time and smaller flush volume => higher temp).

Both the brew temp and pressure will impact the extraction and the resulting flavor in the cup.

[HB]

A change in flow rate will change the brew temperature.

The OPV sets the max brew pressure, not the temp.

You're both correct, but I think krus is referring to the same point Jon made in How to make a beautiful "naked" triple espresso:

In my opinion ristretto tastes better when pulled at slightly cooler temperatures, so flush extra before a ristretto, immediately before you lock the portafilter and brew. Brewing temperature rises in HX espresso machines when running ristretto due to slow flow through the heat exchanger. If the starting temperature is high then the cup will have "burnt edges" in both appearance and in taste.

[RapidCoffee]

As I understand it, the OPV sets the max brew pressure, which is particularly important for ristrettos - but not primarily due to increased brew temperature (an effect seen only in HX machines). Without the OPV, the pressure would otherwise shoot sky high under restricted flow with a vibe pump, and the flavor would suffer (on any type of machine). What am I missing here?

Searching for enlightenment, as usual - John

[HB]

You're missing nothing at all. The flow rate for ristrettos is slower, so the water picks up more heat for HX machines. If you plan on pulling a really tight ristretto, you might add a second or two to the flush. Otherwise you risk going overtemp for fast recovery machines. That's part of the reason I advocate the lowest boiler pressure setting that delivers good steam and desired brew temperature - it allows a wider margin of error since the rebound time is longer. For example, if I daydream 10 seconds too long with Valentina after the cooling flush, it's (almost) forgiven. The Elektra A3 would punish my inattention with dark-rimmed crema and a bitter aftertaste.

[RapidCoffee]

You're missing nothing at all. The flow rate for ristrettos is slower, so the water picks up more heat for HX machines. If you plan on pulling a really tight ristretto, you might add a second or two to the flush. Otherwise you risk going overtemp for fast recovery machines.

Thanks! I've seen this effect many times, but (ahem) unintentionally, while dialing in a grind...

[krus]

I agree with you. Earlier today I played a bit with the expansion valve and it seems as though at the lower settings (9.2 bars) the extraction isn't as rich. I adjusted it back to around 9.8 bars and immediately noticed a fuller, richer flavor with more pronounced body. I don't believe the same brew pressure on a vibe pump and rotary vane pump result in an equivalent extraction. I'm not too sure, but you could be right in believing that different blends have varying optimal brew pressures.

Kurt

[RapidCoffee]

I agree with you. Earlier today I played a bit with the expansion valve and it seems as though at the lower settings (9.2 bars) the extraction isn't as rich. I adjusted it back to around 9.8 bars and immediately noticed a fuller, richer flavor with more pronounced body. I don't believe the same brew pressure on a vibe pump and rotary vane pump result in an equivalent extraction. I'm not too sure, but you could be right in believing that different blends have varying optimal brew pressures.

That's something I need to play with too. I set my pump pressure to the "standard" 9 bars and left it there, and I'm probably missing out on the flavor nuances you describe.

The vibe pump vs. rotary pump issue is very interesting - and AFAIK unresolved. There's one well-known study that found essentially no taste difference between vibe pump and rotary pump La Cimbali Jr models. But based on subjective impressions, others claim to detect significant differences in taste. I'd love to hear more on this topic.

- John

[HB]

But based on subjective impressions, others claim to detect significant differences in taste. I'd love to hear more on this topic.

Me too.

As you know, the Quickmill Vetrano rotary pump espresso machine is currently under review. Chris' Coffee agreed to loan me an Anita as part of updating the Buyer's Guide to the Andreja Premium (the Andreja Premium and Anita share the same boiler and group). Afterall, if the Vetrano's guide were to compare these models, it should be based on side-by-side comparisons, not my memories from a report written 1-1/2 years ago. I don't anticipate any startling revelations, but I'm pleased to have the opportunity to test two machines whose only significant difference is the type of pump. Look for more in a few weeks, e.g., a group taste test at our weekly Counter Culture Coffee espresso lab meeting.

[RapidCoffee]

Me too.

As you know, the Quickmill Vetrano rotary pump espresso machine is currently under review. Chris' Coffee agreed to loan me an Anita as part of updating the Buyer's Guide to the Andreja Premium (the Andreja Premium and Anita share the same boiler and group). Afterall, if the Vetrano's guide were to compare these models, it should be based on side-by-side comparisons, not my memories from a report written 1-1/2 years ago. I don't anticipate any startling revelations, but I'm pleased to have the opportunity to test two machines whose only significant difference is the type of pump. Look for more in a few weeks, e.g., a group taste test at our weekly Counter Culture Coffee espresso lab meeting.

Good idea. That should provide a nice counterpart to the La Cimbali study (and probably some thought-provoking results). Looking forward to it!

- John