a bit more technical - brewing machines

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a bit more technical - brewing machines

Postby dsc » Sun Feb 26, 2012 10:18 pm

Hi everyone,

I'm tinkering with the idea of making an automatic filter brewer, but before I start going wild with the design I was curious if anyone here knows or owns an auto filter / brewed coffee brewer at home? smth like this for example:

http://www.amazon.co.uk/Morphy-Richards ... 397&sr=1-1

?

They are dirt cheap and I reckon brew with boiling hot water, but I'm interested in what internal bits they have. Does it have a pump of some sort? a nozzle? any info is appreciated:)

Regards,
dsc.
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RE: a bit more technical - brewing machines

Postby CakeBoy » Mon Feb 27, 2012 12:39 pm

We would also be interested in a filter design that utilised water at optimum temperatures. There could of course be various designs out there, with some incorporating more technology than others, but as far as I am aware, the majority, if not all, are nothing more than electronic timers between the power supply and what is basically a bog standard filter. In which case, boiling water may be required in those designs (percolator style) to compensate for a lack of a pump to push water at lower temperatures around the system.
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RE: a bit more technical - brewing machines

Postby dsc » Mon Feb 27, 2012 1:40 pm

Hi Cakey,

it is indeed just a simple pipe + boil water approach, which is why those brewers are so sh*t for brewed coffee. I think the main problems in designing a brewer which allows for precise temperature and flow control are:

- dispersion, some sort of brew head would be needed, maybe brew nozzle?

- flow control, roughly 1.5 - 2.5ml per sec which is quite low, I'm looking at various pumps, but most of the do higher flows rather then lower flows

- heating up the water, a standard boiler + pump scenario or pump + thermoblock approach

Any suggestions? feel free to chip in:)

Regards,
dsc.
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RE: a bit more technical - brewing machines

Postby CakeBoy » Mon Feb 27, 2012 2:34 pm

I doubt that I could add anything that you haven't thought of mate. There are others on the forum who will probably be able to offer a meaningful contribution. I have seen the amazing things you have fabricated in the past. I do think these is probably a real market for a proper filter brewing system with temperature contol. We would certainly be interested in buying a unit if you do get anything going. Meanwhile, I will nudge you if any ideas appear in my addled muffin powered brain :)
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re

Postby dsc » Mon Feb 27, 2012 3:18 pm

Lovely! more muffins = more brain power!!:)

Regards,
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RE: re

Postby bruceb » Mon Feb 27, 2012 4:33 pm

I always recommend Technivorm brewers, have had a few good cups from them, but don't know much about their innards. Is that just a simple boiler machine?
BTW, in my experience, the problem with most filter machines is that the water is too cold when it hits the coffee, not too hot. I've measured the temperature on a number of machines and even though the water had to be boiling when it left the boiler it was between 85 and 90°C when it went into the filter. I guess that is the result of loss in the aluminum pipe leading from the boiler to the outlet.
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RE: re

Postby Beanie » Mon Feb 27, 2012 7:30 pm

Why can't the water be abovethe grinds as it heats and then just rely on gravity? As for speed of water flow down...I'm picturing an hourglass concept. I'm also thinking using PID to determine whatever temp...when temp achieved, heating element shuts off and immediately triggers water spout to open for the infusion and brewing to begin. I have simple thoughts.
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RE: re

Postby dsc » Mon Feb 27, 2012 7:44 pm

I've worked with Technivorm, wasn't very impressed, the temp was all over the place and most of the time too high. It works on the same principle as other brewers, water boils in a small tube and the bubbles push the water out. I reckon Technivorm must have insulated tubes to keep the water temp above 90*C.

As for the 'water dump' idea, I've got it on my list, but it's not so great me thinks. You can put a simple solenoid valve to drop the water, control the 'boiler' (it can be a simple open ended container with a heater dropped in the water) with a PID, keep it nice and simple, but you loose the ability to water the grounds evenly in the beginning. If you add a shower screen for even extraction, the water will be gone in an eye blink as it will definitely flow faster than 1.5 - 2.5 ml/s. With a pump you can build up the pressure a bit and force the water where you want it (using a nozzle), spraying, dripping, doing whatever. With gravity, there's limitations.

Regards,
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Postby easylife » Mon Feb 27, 2012 10:51 pm

DSC - You might find this interesting to follow up.

The ECBC and the SCAA both test and evaluate commercially available drip brewers.

ECBC tests are defined here:-

http://www.kaffe.no/certification-standards/

SCAA tests are defined here:-

http://scaa.org/?page=cert2

Both organisations approve the technivorm brewers as meeting their standards.

The ECBC also approves the the Melitta Excellence Thermo-steel (I might have that title slightly wrong as it's a clumsy translation from German.) and it's direct equivalent the Bonavita machine in the USA gets approval there by the SCAA.

It seems to me they both go about things in a very scientific way using precise measurements, so It's strange your own results from a technivorm didn't measure up.

As it happens I have both a technivorm and the Melitta thingie. Both work extremely well, probably because they have hefty (1400w) heaters compared to almost all the other domestic brewers around. Also - and it's a brilliant (not) bit of design in most other machines, that in those the tube with the hot water in often goes directly through the cold water tank.....

Got slagged off on here some time ago for even thinking of buying an auto drip machine - seems it isn't purist enough for some. So take care !

Ho hum. :roll:

Don't a lot of the commercial machines pre-boil the water in a tank up top, and then let it drip down through ? Pretty sure the Bunn machines do anyway.
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Postby lukas » Mon Feb 27, 2012 11:39 pm

The Technivorm isn't all that bad. Well actually it's the best auto drip for the home I've ever owned - it reproducibly (!) makes delicous filter coffee. Manual brews can be better if you get everything right, but it takes so much more effort. Also, I haven't yet found a way to reliably brew more than 750ml with any manual method. I always seem to mess those up :/

An auto drip that reliably gives you the quality of a really well done filter brew on the other hand, that would be heaven. Bonus points for brewing anything from 250ml to 1.5l equally well (for me, manual brews shine from 150 to 500ml, the moccamaster does from 500ml to 1.25l).
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Postby dsc » Tue Feb 28, 2012 11:51 pm

Cheers for the input guys!

easylife: thank you for the links, will go through them. It baffles me that Technivorm somehow got through the uniformity of extraction test, it simply spits out water from 3-5 holes directly into the middle of the filter:O I've also done some quick temperature tests on the Technivorm (with an Omega datalogger) and the temps were all over the place, ranging from 90-96degC, this is with a thermocouple in the metal tube above the grounds. Why the hell SCAA is using RTDs stuck in the coffee bed (which screws up the readings even more) is beyond me.

lukas: I think volume shouldn't be a limit if the design is right, maybe a different nozzle can be used for larger brews.

Regards,
dsc.
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Postby easylife » Wed Feb 29, 2012 10:26 am

Are you sure you were not using a faulty unit ? or perhaps scaled up ? My Technivorm doesn't exactly flow evenly from all the holes, but it doesn't seem to as you say spit out water from 3-5 holes in the middle. The Melitta machine does do a better job of this, but I prefer to use the Technivorm - it's much easier to clean for one thing.

I guess a problem with almost all automatic drip filters is that the bloom on the grounds rises to the top and doesn't seem to get mixed in thoroughly with the rest of the "slurry". I know some folk do a quick stir for that reason. I've tried doing so and not doing so, and it doesn't seem to make much difference to what is in the final brew. I always do stir syphon brews though, as otherwise things can get hardly mixed at all.

Perhaps that's an issue you can address. I think the Bunn Trifecta attempts to do just that.

I don't know enough about ideal brewing standards to critique the SCAA and ECBC test methods, but I assume they want to test the temperature where the extraction itself takes place rather than anywhere else in the process. The water temperature in the spray arm won't necessarily be the same as when it mixes with everything else at the point at which it hits the coffee.
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re

Postby dsc » Wed Feb 29, 2012 2:55 pm

Hi easylife,

I agree that TechniVorm I was using was a bit scaled up, but I'm sure that not to a point of affecting the dispersion. The arm that delivers the water only has 3 or 5 holes anyway, so you end up with a single / dual stream of water hitting the coffee straight bang in the middle (most of the time). A shower screen like an espresso machine brew head would be much better, but then you are delivering quite a high amount of fluid per sec, due to the amount of holes in the dispersion screen. I might simply borrow my parents Technivorm for a few weeks and play with it more, maybe mod it a bit, as it has a tank and a heating plate that I can work with, throw in a pump, an additional thermoblock and I'm home:)

Regarding SCAA temp measurement I was surprised by the RTD sensor they use, it's a rather slow method of measuring temperature, normally one would stick a thermocouple where you want to check temps and datalog it to death.

Regards,
dsc.
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Re: re

Postby easylife » Wed Feb 29, 2012 7:09 pm

dsc wrote:I agree that TechniVorm I was using was a bit scaled up, but I'm sure that not to a point of affecting the dispersion. The arm that delivers the water only has 3 or 5 holes anyway, so you end up with a single / dual stream of water hitting the coffee straight bang in the middle (most of the time).


Is it an old machine ? Current models have 9 holes.

Have you looked at something like the Bunn Phase Brew machines ? They already seem to be quite close to what you are intending to develop. Not sure you can get them here. They're really designed for the US where running a reasonably powerful instantaneous heater as in a drip machine is tricky due to their low domestic voltage. I think most of larger Bunn machines and some domestic ones pre-heat the water in a boiler then release it in a steady flow.

What shape of filter basket are you proposing to use ? Presumably that will also influence the pattern of water distribution you want to achieve.
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RE: Re: re

Postby dsc » Sun Mar 04, 2012 8:24 pm

Not sure how old it is, but it might as well have 9 holes in all honesty, I don't recall the exact amount now.

I haven't thought about filter baskets at all, just your ordinary V60 / Kalita under the brew head nozzle.

Regards,
dsc.
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