Measuring SG using capacitance...Arduino brewing

[jodrell]

I'm looking to improve on my current Magic Beer Fridge (fridge & light bulb thermostatically controlled) by doing a second build out using the Arduino processor board.

I should be able to replicate the temperature control with no problems, be able to feed into from sensors to a database somewhere and even control the temperature setting remotely, but what I'd really like is to be able to measure the Specific Gravity of my brew as well.

I've had a couple of ideas of how I might do this but the best, assuming it works, would be to measure the capacitance of the liquid which should vary with it's density. I guess I'd need to start from a known point measured some other way (probably manually with my refractometer) and then use the changes in capacitance to plot the changes in SG.

Just wondering if anyone had tried this and/or knew where I could find some more information out??

 

[prolix]

Jodrell, I love it!

There may be one or two technical difficulties like the capacitance change being too low or fluctuating with the differing products and so being not only non linear but brew specific.

Oh and bubbles, not Michael Jacksons monkey but the round ones will form in the plates thereby reducing the actual surface area of the plate and yeast settling on the plates will affect it too.

Apart from that go for it!

I would suggest measuring the capacitance of known sugar soultions first to get a rough idea then add vodka to them to see the effect alcohol has on the system, the measurments not yours after drinking the experimental fluids. :

Good luck mate this could be the gadget of the future as famous a TC and WOW or you might just have a lot of fun tinkering, it's a win win

 

[richc]

I have a nasty feeling you are going to find your data swamped by other effects. I have no idea what the various things effecting the dielectric coefficient of wort will be but I don't think this is going to be simple.
I'd be very tempted to try and measure the gravity optically (but then again I did specialise in optics during my instrumentation MSc many years ago). I think it would be pretty easy to build something based on a refractometer using a LED and a linear CCD type of arrangement.

 

[richc]

Hmm, you might get something from capacitance though I think the effects from alcohol and sugars might conflict. The dielectric constant for water is 80, ethanol is 24.3 and syrup (the closest thing to wort I could find) varies from 50-80.

 

[bob downe]

How about a float connected to an LVDT. You could perhaps adapt an actual hydrometer, by winding coils around the stem and use this as part of your LVDT.

Linear and accurate. Just need to calibrate to known liquid density's.

http://en.wikipedia.org/wiki/Linear_var ... ransformer

 

[jodrell]

yeah, those two were my other ideas.

The float idea was where I started from but I just have the feeling that it'll turn into a bit of a mess and be a bit tricky to clean and steralise.

The optical method means either removing a sample from the wort each time you want to take a reading (and I'd be wanting to auto monitor every 5 minutes if I can) or using a laser to measure refraction at a boundary layer. You can't do that at the air-wort boundary layer because of the head formed by the yeast so I was thinking you could mount a small laser under the surface of the wort onto a receiving point and measure the change in refraction and the SG changes.

You'd have an air/glass boundary then a glass/wort boundary but the air/glass one should remain constant so I guess that would work but I'm worried about securing the laser effectively, especially inside a plastic vessel

 

[unclepumble]

I think you might be overcomplicating things for yourself, the big boys don't do it like that they take samples daily and manually input the SG each time.

But if you like complication,I think you could also use an ultrasonic level sensor in the lid and use it to measure a hydrometer Tip, when the gravity drops so does the hydrometer, most Utrasonic sensors give a 4-20MA signal and can be set up for varying sensitivity.

I'd stick with daily samples though, at least you get a free drink after.

UP

 

[jodrell]

yep, I know it's a bit overkill but it'd be nice to get something working.

BTW I only need a couple of drops of liquid for the refractometer...that's hardly a refreshing pint ;-)

 

[bob downe]

What about 'sniffing' the beer using a gas alcahol sensor. Perhaps you could mount a pipe to your fermenting bucket with an alcahol gas sensor in the end.

At a given temp, for a given alcahol content you could expect a given reading from catching ethanol vapour from the beer.

Of course, accuracy and reliabilty are factors but hey, that's what research and development is all about.

 

[unclepumble]

yep, I know it's a bit overkill but it'd be nice to get something working.

BTW I only need a couple of drops of liquid for the refractometer...that's hardly a refreshing pint ;-)

The problem with refractometers is they don't work very well when you add alcohol, as alcohol throws the reading off, refractometersare good for sugary wort but once you start to make alcohol using yeast, you may as well throw the refractometer away.

You can use one but only by doing a very complicated mathmatical calculation, after taking a reading, & then its only an estimate.

For a truer reading you need to sample using a high end calibrated spectrophotometer , & that would be true overkill for a home brew.

Soldier on with your project, if that's what floats your boat, though I think you would be better to spend your spare time and money on acurately controlling your fermentation temperature, or sorting out a device to analyse your water additions etc it would be time better spent, I fear, & you would get a better tasting beer out of your efforts.

UP

 

[jodrell]

The problem with refractometers is they don't work very well when you add alcohol, as alcohol throws the reading off.

I've got some software I throw the Brix reading into during Fermentation to convert it to SG. I read the first few and did a traditional reading with my hydrometer and it seemed pretty close

Soldier on with your project, if that's what floats your boat, though I think you would be better to spend your spare time and money on acurately controlling your fermentation temperature, or sorting out a device to analyse your water additions etc it would be time better spent

I've got the temperature under control using a heated thermostatically controlled Fridge but interesting that you mention the water...I'm wondering if I could/should use some of the kit from my aquarium to measure water quality. What sort of things should I be looking for and trying to adjust/correct?

Essentially I'm running this project because I'm a geek and think it'd be nice to be able to view the development of my beer live online while I'm at work...and with that live monitoring I might see that the temperature if bouncing rather than remaining fairly stable and be able to make improvements

 

[alexe]

Did you get anywhere with this? I've been thinking about something like this too... (for the same reasons - geek, want to monitor beer fermentation, etc)

 

[jodrell]

I didn't manage to get anywhere myself but I found and invested in a Kickstarter project called BeerBug that achieves the same thing. I'm due to receive mine in April I think...I'll let you know how it works out.

 

[alexe]

I've heard of the Beerbug - interested to see how it works! Keep us posted...

 

[SpringSteam]

Old post i know, but i would like to know how the BeerBug worked/works out !? :)

 

[DanST]

Capacitance will change with cell density and size as the yeast cells will act like capacitors. There are probes used in industrial cell culture which work on this principal.

I haven't used these with yeast cultures (they are pleasure not business! ) but I'd suspect it would be difficult to determine if the cause of a change in capacitance was due to changes in SG from ethanol production or changes in the amount or health of the yeast.

sorry probably irrelevant now, didn't see the 2nd page of replies or the date!