CoffeeJack: One Million Dollars of Bad Coffee

[I wanted a rude username]

[m98]

Now I haven't watched all of Thunderfoots reasoning for why that espresso maker shouldn't work, but isn't he effectively arguing that it would be impossible to inflate a regular road bike tire using a handpump? Or more general, that a pump can't increase the pressure of a medium beyond the peak force put into driving it? That's absolutely ridiculous.

[Cyberdragon]

Now I haven't watched all of Thunderfoots reasoning for why that espresso maker shouldn't work, but isn't he effectively arguing that it would be impossible to inflate a regular road bike tire using a handpump? Or more general, that a pump can't increase the pressure of a medium beyond the peak force put into driving it? That's absolutely ridiculous.

It's clear that the people making the product have no idea how to make coffee, just judging from the awful demo video they put out, and there product does have design flaws (could crush the cup if you really smashed on it). HOWEVER, Thunderfoot, who usually makes rants that have a point, keeps comparing this thing to an electric coffee machine. "But you still have to boil the water!" No shit Sherlock! It wasn't until the second video that he even mentioned more than once a manual coffee maker (comparing the stresses on the container), and it seems like he has no idea of what this machine is actually trying to be...which is A FRENCH PRESS! I guarantee he has no idea how to properly use one either and would make just as bad of a coffee with a real high end press as the numpties making this thing. He really should do a proper video comparing it solely to other manuals and not complain that it doesn't boil or pump like an automatic machine does, because that's not the intended market.

[PlainName]

keeps comparing this thing to an electric coffee machine

That seems to be his modus operandi - create a strawman he can burn down with spectacular ranting and job's done. But it gets him the bucks.

[jonroger]

He seems to believe that his machine with an 8 second extraction time is superior.   But this is not even close to the Italian Espresso National Institute standard of 25 ± 5 seconds.   Typed while sipping actual espresso from a direct lever espresso machine.

[ebastler]

Why would I take advice on coffee from someone who keeps calling it "expresso"? 
Seems clear that Thunderfoot is out of his depth here.

Nevertheless, I'm not a fan of the Coffeejack design either. It is advertised as making espresso-style coffee ("barista style"), and the water temperature will certainly be too low for that by the time it has been poured into the room-temperature reservoir and worked its way through the manual pump. Also, the whole thing seems a bit shaky during the pumping process, due to its top-heavy design and relatively small footprint area.

If you want a simple, low-cost way to make "somewhat simliar to espresso"-style coffee, the Italians have solved this since the 1940s with the "moka pot" stove-top coffee maker. Available in various sizes, cheap and simple, lasts forever. And yes, I know it's not espresso since the brewing pressure is much lower (just like in the CoffeeJack...)

[PlainName]

"moka pot" stove-top coffee maker

Got one. Has the disadvantage that you need a stove top. This CoffeeJack just wants hot water, so it would be conceivable to use wherever there is a kettle or one of those hot water machines. Which also kind of gives it green credentials since your stove top isn't warming up the kitchen as well as the water

[Kilrah]

but isn't he effectively arguing that it would be impossible to inflate a regular road bike tire using a handpump?

Not impossible, but inflating a tire manually to 10+bar definitely would be extremely painful...

[PlainName]

I thought he was a physicist or something. The bicycle tyre has a large volume so to compress it 10:1 you're need 10x more volume (is that right or have is it more?), which is a lot of pumping. The CoffeeJack, on the other hand, should have hardly any volume so would need relatively little pumping for the same pressure increase. And it wouldn't necessarily be harder either since there is the small matter of leverage to consider.

[Cyberdragon]

and the water temperature will certainly be too low for that by the time it has been poured into the room-temperature reservoir and worked its way through the manual pump.

It's not at all, any more that pouring water from the kettle into a different container to steep tea. Look up how to use a french press. Water has a relatively high specific heat.

[Terry01]

Eh?  Handpump 10 BAR!?

I inflate my wheelchair tyres to 25 ish PSI which google conversion says is only 1.7 BAR!
I know when my tyres are fully pumped up properly when the pump takes my weight standing on the foot plate and it doesn't compress no more. I don't bounce to get more pressure or anything like that, just keep pumping steady till it takes my weight. When I check the dial it's always dead on.
It's one of those double barrel things that pumps the tyre up pronto, it's meant for car tyres.

I wouldn't like a slap on the head from the guy who can hand pump 10 BAR!! Must be Popeye's BIG brother or something!

On a side note, I was in hospital quite ill a few months ago and dropped 2.5 stone in weight. It doesn't seem to affect the pumping process any, I thought it would. I still just pump till it takes my weight and the 2.5 stone weight difference doesn't seem to matter any.

Oh I weight about 10 stone just now, maybe a wee bit over...

[ebastler]

Look up how to use a french press.

Not sure why you keep relating the Coffeejack to a French press. The similarities are superficial only -- both take hot water, have a plunger, have a glass jar.

But the extraction principle in the French press is obviously very different; the coffee grinds stay in contact with the water for several minutes, floating in suspension. In contrast, the CoffeeJack claims "barista style" coffee and an extraction process similar to espresso machines.

[Psi]

Look up how to use a french press.

Not sure why you keep relating the Coffeejack to a French press. The similarities are superficial only -- both take hot water, have a plunger, have a glass jar.

But the extraction principle in the French press is obviously very different; the coffee grinds stay in contact with the water for several minutes, floating in suspension. In contrast, the CoffeeJack claims "barista style" coffee and an extraction process similar to espresso machines.

Yes, that is the key point. They claim it can do a proper espresso extraction with that level of pressure.

[thm_w]

Eh?  Handpump 10 BAR!?

Its not unusual for a bike to use ~120psi (8 bar) rated tires. You can get small telescoping hand pumps that are capable of achieving that. It takes effort and a floor pump is way better, but, you don't want to carry those around in your bag.

https://www.chainreactioncycles.com/ca/en/lifeline-performance-cnc-mini-pump/rp-prod155349 (120 psi)
https://www.chainreactioncycles.com/ca/en/topeak-race-rocket-hpx-master-blaster-road-pump-aw17/rp-prod165286 (160 psi - 11 bar)

[Cerebus]

Eh?  Handpump 10 BAR!?

I inflate my wheelchair tyres to 25 ish PSI which google conversion says is only 1.7 BAR!
I know when my tyres are fully pumped up properly when the pump takes my weight standing on the foot plate and it doesn't compress no more. I don't bounce to get more pressure or anything like that, just keep pumping steady till it takes my weight. When I check the dial it's always dead on.
It's one of those double barrel things that pumps the tyre up pronto, it's meant for car tyres.

I wouldn't like a slap on the head from the guy who can hand pump 10 BAR!! Must be Popeye's BIG brother or something!

On a side note, I was in hospital quite ill a few months ago and dropped 2.5 stone in weight. It doesn't seem to affect the pumping process any, I thought it would. I still just pump till it takes my weight and the 2.5 stone weight difference doesn't seem to matter any.

Oh I weight about 10 stone just now, maybe a wee bit over...

Have ye nay heard of levers and hydraulics laddie?

I can lift a side of my car (approx weight 1200kg) using a hydraulic jack with negligible effort. The actual piston that holds the car up has a diameter of 20mm, so an area of 2pi(0.01m)² = 0.000629 m². It's holding 1/2 the car's weight, say 600 kg, say 6000N; so the pressure on the backside of that piston is  6000N/0.000629m² = 9.55 MN/m² = 9.5 MPa = 95.5 Bar.

The magic that turns my minimal effort (perhaps 10-15 kgf) into almost ten times the pressure figure you think neigh impossible is a lever driving a small area piston. There's no reason that the same principle couldn't be applied to shifting the 30-40 ml of water at 10 Bar over 30 seconds that's required to make a shot of espresso.

Let's work it out. Magic numbers for espresso: 9 bar brewing pressure, shot of 40 ml delivered over 30 seconds.

We need 40 ml of water delivered over 30 seconds. Let's suppose a piston with a cross sectional area of 1.33 cm², move that piston through 1 cm and it will deliver 1.33 ml of water. Do that 30 times (once a second) will deliver 40 ml. Working against a pressure of 9 Bar (900 kPa) it will need 900,000 N/m², applied over 0.000133m² => ~120 N applied to the piston. Connect that piston to a lever with a 10:1 ratio and you will need to apply a force of 12 N (1.2 kgf) over a distance of 10 cm. (20:1 might be a better ergonomic compromise, 20 cm movement, 6N force).

If you can pump a lever through 10 cm, working against 1.2kgf, 30 times in thirty seconds then you can supply both the power and the pressure needed to brew a shot of espresso. I don't think too much of the machine from the video, but in principle it could be made to work.

[james_s]

"moka pot" stove-top coffee maker

Got one. Has the disadvantage that you need a stove top. This CoffeeJack just wants hot water, so it would be conceivable to use wherever there is a kettle or one of those hot water machines. Which also kind of gives it green credentials since your stove top isn't warming up the kitchen as well as the water

We have a really old one of those at our cabin, it's been there for as long as I've been part of the family. I had no idea what it even was until last summer when we took a friend from out of town there and he was looking for coffee in the morning and found it, turns out it works just fine. My partner and I both think coffee tastes vile and never drink it but I do think many of the machines for making it are fascinating for some reason.

[Terry01]

Eh?  Handpump 10 BAR!?

I inflate my wheelchair tyres to 25 ish PSI which google conversion says is only 1.7 BAR!
I know when my tyres are fully pumped up properly when the pump takes my weight standing on the foot plate and it doesn't compress no more. I don't bounce to get more pressure or anything like that, just keep pumping steady till it takes my weight. When I check the dial it's always dead on.
It's one of those double barrel things that pumps the tyre up pronto, it's meant for car tyres.

I wouldn't like a slap on the head from the guy who can hand pump 10 BAR!! Must be Popeye's BIG brother or something!

On a side note, I was in hospital quite ill a few months ago and dropped 2.5 stone in weight. It doesn't seem to affect the pumping process any, I thought it would. I still just pump till it takes my weight and the 2.5 stone weight difference doesn't seem to matter any.

Oh I weight about 10 stone just now, maybe a wee bit over...

Have ye nay heard of levers and hydraulics laddie?

I can lift a side of my car (approx weight 1200kg) using a hydraulic jack with negligible effort. The actual piston that holds the car up has a diameter of 20mm, so an area of 2pi(0.01m)² = 0.000629 m². It's holding 1/2 the car's weight, say 600 kg, say 6000N; so the pressure on the backside of that piston is  6000N/0.000629m² = 9.55 MN/m² = 9.5 MPa = 95.5 Bar.

The magic that turns my minimal effort (perhaps 10-15 kgf) into almost ten times the pressure figure you think neigh impossible is a lever driving a small area piston. There's no reason that the same principle couldn't be applied to shifting the 30-40 ml of water at 10 Bar over 30 seconds that's required to make a shot of espresso.

Let's work it out. Magic numbers for espresso: 9 bar brewing pressure, shot of 40 ml delivered over 30 seconds.

We need 40 ml of water delivered over 30 seconds. Let's suppose a piston with a cross sectional area of 1.33 cm², move that piston through 1 cm and it will deliver 1.33 ml of water. Do that 30 times (once a second) will deliver 40 ml. Working against a pressure of 9 Bar (900 kPa) it will need 900,000 N/m², applied over 0.000133m² => ~120 N applied to the piston. Connect that piston to a lever with a 10:1 ratio and you will need to apply a force of 12 N (1.2 kgf) over a distance of 10 cm. (20:1 might be a better ergonomic compromise, 20 cm movement, 6N force).

If you can pump a lever through 10 cm, working against 1.2kgf, 30 times in thirty seconds then you can supply both the power and the pressure needed to brew a shot of espresso. I don't think too much of the machine from the video, but in principle it could be made to work.

So ... more brains … less brawn?   

[KL27x]

You can see in the video, the coffee starts to emerge after only a couple pumps, and the flow rate appears fairly high.  This reminds me of the stuff in the Skymall catalog on the seatbacks of the airplanes, back in the 90's. Wild claims. High price. Latest technology. And made to appeal to the luxury impulse purchaser.

[thinkfat]

You can of course pressurize any volume to 10 bar, the thing with making a decent espresso is that you need these 10 bar constantly while you force the hot water through the ground coffee. For the CoffeeJack it means you need to reach 10 bar every time you push the pump. With one hand. That's going to leave some serious dents in your palm.

[thinkfat]

We need 40 ml of water delivered over 30 seconds. Let's suppose a piston with a cross sectional area of 1.33 cm², move that piston through 1 cm and it will deliver 1.33 ml of water. Do that 30 times (once a second) will deliver 40 ml. Working against a pressure of 9 Bar (900 kPa) it will need 900,000 N/m², applied over 0.000133m² => ~120 N applied to the piston. Connect that piston to a lever with a 10:1 ratio and you will need to apply a force of 12 N (1.2 kgf) over a distance of 10 cm. (20:1 might be a better ergonomic compromise, 20 cm movement, 6N force).

If you can pump a lever through 10 cm, working against 1.2kgf, 30 times in thirty seconds then you can supply both the power and the pressure needed to brew a shot of espresso. I don't think too much of the machine from the video, but in principle it could be made to work.

This will work if the chamber that holds the ground espresso powder has the same cross sectional area, right? If the area is larger, the pressure will drop proportionally.

[PlainName]

the pressure will drop proportionally

And rise proportionately the other way?

Anyone taken into account the chamber volume less the coffee grounds volume? Could be very small indeed.

[Cerebus]

We need 40 ml of water delivered over 30 seconds. Let's suppose a piston with a cross sectional area of 1.33 cm², move that piston through 1 cm and it will deliver 1.33 ml of water. Do that 30 times (once a second) will deliver 40 ml. Working against a pressure of 9 Bar (900 kPa) it will need 900,000 N/m², applied over 0.000133m² => ~120 N applied to the piston. Connect that piston to a lever with a 10:1 ratio and you will need to apply a force of 12 N (1.2 kgf) over a distance of 10 cm. (20:1 might be a better ergonomic compromise, 20 cm movement, 6N force).

If you can pump a lever through 10 cm, working against 1.2kgf, 30 times in thirty seconds then you can supply both the power and the pressure needed to brew a shot of espresso. I don't think too much of the machine from the video, but in principle it could be made to work.

This will work if the chamber that holds the ground espresso powder has the same cross sectional area, right? If the area is larger, the pressure will drop proportionally.

No, if all the chambers are directly connected they are at the same pressure. This is a basic property of all fluids (including those fluids called gasses). Pressure drops/rises can only happen under flow conditions across restrictions that are small and/or long relative to the viscosity of the fluid under consideration. Under steady state non flowing conditions the pressures equalize.

[ebastler]

No, if all the chambers are directly connected they are at the same pressure. This is a basic property of all fluids (including those fluids called gasses). Pressure drops/rises can only happen under flow conditions across restrictions that are small and/or long relative to the viscosity of the fluid under consideration. Under steady state non flowing conditions the pressures equalize.

Right. You can scale up force by driving a large piston from a small one, but that does not change the pressure inside this hydraulic system. Of course, the large piston will move correspondingly more slowly, so power (and work) are conserved.

But one could then have that large piston drive another small piston (by bolting them together mechanically), and build higher pressure in a secondary fluid circuit. The primary combination of small and large piston just serves as a lever -- and could be replaced by a classical mechanical lever too.

[Cerebus]

No, if all the chambers are directly connected they are at the same pressure. This is a basic property of all fluids (including those fluids called gasses). Pressure drops/rises can only happen under flow conditions across restrictions that are small and/or long relative to the viscosity of the fluid under consideration. Under steady state non flowing conditions the pressures equalize.

Right. You can scale up force by driving a large piston from a small one, but that does not change the pressure inside this hydraulic system. Of course, the large piston will move correspondingly more slowly, so power (and work) are conserved.

But the final thing we are trying to move is not another piston, it's a small quantity of water through a bed of coffee grounds at (an industry standard) pressure of 9 bar. We're just trying to pressurize water (an in-compressible fluid) and move a mere 30-40 ml through some ground coffee. You can do this with a small piston and, with the help of a short lever, very little force. If you apply X Pa pressure to the surface of that small piston, then the same X Pa pressure is applied to all surfaces in all connected vessels - this is the basic magic that makes hydraulics work.

We do no work, in the physics sense, in pressurising the water - we pressurise the water by applying a force to the small piston. We do no work until the piston moves. The work that we are trying to do is to overcome the fluid drag forces involved in moving water through (slightly compressed) ground coffee, it's not a great deal of work - based on my earlier premise it's 120N moved through 0.3m = 36 J, done over 30 seconds that's a power requirement of 1.2W (excluding losses). If it helps, think: pressure = voltage, current = water volume moved per second, the coffee puck = a resistor and the interconnected pressure chambers = a wire.

But one could then have that large piston drive another small piston (by bolting them together mechanically), and build higher pressure in a secondary fluid circuit. The primary combination of small and large piston just serves as a lever -- and could be replaced by a classical mechanical lever too.

Yes, you could replace a small piston/short lever system by a big piston/large lever system. That's already done and indeed was the standard form of espresso machines for many years:



but this (a small domestic lever machine) is not exactly pocket or shoulder bag size - heck it's not even rucksack sized. From the bottom to the top of the lever is about 500mm (height excluding the lever 320mm).

[KL27x]

Exactly.

Water is incompressible. So watch the video again, Cerebus.

When you let go of the lever on an espresso machine, the coffee stops coming out, right? It doesn't continuously spew coffee out like diarrhea, once you hit that 10 bars. That coffee leaving is taking the pressure with it. What is your storage medium for all this pressure? A big pressurized air tank? I don't think pressurized air and boiling water are a good mix in chintzy consumer garbage that you operate within arms reach of your face.

This is some kinda hybrid drip coffee maker thing that you can speed up a little to make extra weak coffee (or use 10x as much grounds to start), not espresso.