Moka Pot - A Crema MONSTER. Wait What?? - Page 3

Coffee preparation techniques besides espresso like pourover.
jpender

#21: Post by jpender »

cari66ean wrote:Your analysis here is rather contradicting: "Higher heating rate means a faster flow. A faster flow requires higher pressure. Higher pressure requires a higher temperature."

Ok... so a "higher heating rate means a faster flow. A faster flow requires higher pressure". Well if this is the case, wouldn't you agree that the higher heating rate might simply be the cause for higher pressure?

Again, it's not the static temperature of the water per se that is creating pressure, but the increasing temperature expanding the water and especially the trapped air within the chamber.
I don't understand what you see as a contradiction. Flow and pressure are correlated. As a first approximation one can use Darcy's Law to model the relationship. Coffee pucks are complicated and they change as the brew progresses but nonetheless as a general rule increased flow requires increased pressure.

The pressure is primarily due to the vaporization of the water and secondarily to the expansion of the fraction of trapped air. Liquid expansion plays an insignificant role. Because the liquid-vapor is not in equilibrium you can't use the steam tables. The vapor is cooler than the liquid in the boiler. This difference is exacerbated by the heating rate. A very slow heating rate would be quasi-static. That's one of the two reasons I think it would result in the lowest possible temperature. The other is that the flow rate would be almost zero so the required pressure would be at a minimum.

This is just basic physics. You can read an excellent paper on moka pot physics written by Luciano Navarini. It's over ten years old but still probably the best theoretical and experimental paper on the subject.

http://www.msc.univ-paris-diderot.fr/~p ... ticle2.pdf

Baratza: skilled in the art of grinding
Sponsored by Baratza
jpender

#22: Post by jpender »

cari66ean wrote:It's a bit funny when you say you think I'm wrong, yet it's such an easy thing to try and clearly see the results of. Go ahead and crank up the heat on your Brikka and you'll see a rather quick extraction with a non-burnt fairly cool coffee. Turn the heat down to medium and it will take longer with a hotter coffee that might already start getting the "characteristic" (=because people are doing it wrong) burnt moka taste. Turn the heat down to low and you might wait for ages for the coffee to sputter out - if it even does and you're going to get an ultra bitter coffee for sure.
Like most people who use a moka pot or Brikka I've experimented with the stove setting. My experience is different than yours. I long ago came to the conclusion that a high heat setting didn't work well. I haven't actually measured the temperature in my Brikka. It's not trivial to embed a sensor. You could measure the temperature in the top of the pot or in your cup but who is to say how well that correlates? There is a nice video with graphs of the internal temperature of a Brikka. Heating rate wasn't looked at but it's interesting nonetheless.

I have embedded sensors in a regular moka pot. For a while I had a pot with a thermistor just below the coffee puck.



I admittedly didn't methodically vary the stove setting and record different profiles but my recollection is that a moderate heat setting was best. I could do this again. It would take me a few days to set it up. Maybe I'd be surprised.

DaveB

#23: Post by DaveB »

I had never heard of the Brikka prior to seeing this thread. I found this, which might be helpful to others. The comments are worth reading as well:

http://101coffeemachines.info/moka/brik ... a-express/
Von meinem iPhone gesendet

cskorton

#24: Post by cskorton »

I used to use a basic bialetti moka pot before I got into espresso and I could consistently get thick crema with Neapolitan blends that contained large amounts of robusta. I found that the amount of robusta in a blend was the key to getting thick crema.

Unfortunately, I think folks on this board gravitate towards the kind of equipment they have and it's effects in the cup. While equipment will make a difference, the biggest difference maker that newer folks always overlook are the kind of coffee they're using and the skill of the person making it.

Of course, with that said, I did notice a big improvement in the cup when I moved to a espresso machine from a moka pot, with even more body and crema.

cerradodude

#25: Post by cerradodude »

Interesting thread. The Brikka has potential, IMO it's capable of better things than the moka pot, but not quite as good as serious espresso machine. The good news is that it's a bit easier to maintain than a serious machine. During the pandemic my Brikka, with some high-percentage robusta classic blends, has become my daily driver: it's reliable and I can stock up for a while, so it reduces the need to go out in public.

Also, this guy has become the nexus of Brikka twitter. Lots of blends and origins have produced an impressive *looking* beverage:

https://twitter.com/hugowiz/status/1349997055255707648

Finally, I'm not trying to out OP here, but I'm wondering if their crema isn't a result of the old cream of tartar trick? I've been looking online to see parameters for it, but I can't find any. Do any of you remember how to do it???

cskorton

#26: Post by cskorton » replying to cerradodude »

Yeah, I agree with your espresso assessment. Even somewhat suboptimal espresso I used to pull on my old barista express was better than the best stuff I could pull out of a moka pot.

Does anyone else find it ironic that a lot of these bleeding edge profile machines more or less are reproducing pressures similar to a moka pot? Maybe not all of them (slayer and blooming shots come to mind) but anything around 2 bar seems to be on par with a moka.

jpender

#27: Post by jpender »

cskorton wrote:Does anyone else find it ironic that a lot of these bleeding edge profile machines more or less are reproducing pressures similar to a moka pot? Maybe not all of them (slayer and blooming shots come to mind) but anything around 2 bar seems to be on par with a moka.

Moka pot pressure typically does not exceed 1 bar.

Weber Workshops: tools for building better coffee
Sponsored by Weber Workshops
cskorton

#28: Post by cskorton »

jpender wrote: Moka pot pressure typically does not exceed 1 bar.
You are absolutely right. I believe though that differences of 1 bar are indistinguishable in the cup.

Jeff
Team HB

#29: Post by Jeff »

In my experience, dropping below around 4 bar tends to transition out of "espresso" and into moka-like or early 20th century "caffe espresso" (steam driven, prior to levers). Exceeding somewhere around 9 bar also impacts the flavor, often in a negative way.

This is separate from the flow-rate effects. Within, say, a 4-9 bar range, the flow-rate change with pressure tends to be less as the flow rate seems to be proportional to the square root of the pressure; a 10% change is pressure is very roughly a 5% change in flow.

Note: These are brew-chamber pressures, which tend to be a bit lower than pump or OPV pressures.

jpender

#30: Post by jpender »

Are there really espresso machines that operate at 2 bar?