No-contact Device For Measuring Fermentation Progress

[chovain]

I had an idea for a device to keep track of how far through fermentation a beer was. To be honest, I have no plans to actually build this, but I'm interested in hearing what people think of it.

I have heard of ultrasonics being used to measure the density of a liquid in a tank or pipe, but apparently this measurement gets confused between alcohol and sugar (like a refractometer does), and floaties (unlike a refractometer).

My idea requires that you can calculate the amount of sugar fermented from the CO2 released. It also requires that the fermenter be sealed.

Here's how it would work: The device would consist of an air-tight, non-flexible chamber of known volume. The chamber would have in inlet pipe and outlet pipe connected, with a gas solenoid on each. The inlet would be connected to the air-lock (or directly to the fermenter if you could sanitise the device.

Using a relatively good pressure sensor (The $15 HP03D can get 0.1hPa precision), and a temperature sensor, it should be possible to allow the chamber to charge up (close outlet, open inlet) until the pressure builds up a little. Close the inlet and open the outlet, and the pressure will equalise. The device can measure the quantity of gas that has been released by taking the difference of the pressure measurements, and factoring in chamber volume and temperature.

It could be made even more accurate by putting a second pressure sensor on the outside of the device, so that it knew what the atmospheric pressure was at each release.

Does anyone see a problem with this idea (apart from being expensive)?

 

[Adamt]

It'd likely be a lot easier to just have your fermenter on a set of high-accuracy scales.

Then mass CO2 evolved = difference.

Convert to molecular quantity, etc etc.

 

[Guest Lurker]

It'd likely be a lot easier to just have your fermenter on a set of high-accuracy scales.

I think I recall someone on HBD came to the same conclusion, but rather than use conventional scales proposed the fermenter is slung on a beam balance, with a bag of pennies or similar at the counter balance, and you keep count of how many you remove to keep it balanced.

 

[newguy]

The biggest problem with measuring the weight of the fermenter has to do with the relatively small change in mass. Big changes are easy to pick up, but when the changes are small, things get much more difficult. 20l of 1.050 wort will weigh 21kg, and if the FG was 1.000 the beer will only lose 1kg. That sounds like a lot, but it's just a tiny fraction of the total. Add to that the mass of the fermenter itself and the rig/stand, and trying to measure the weight of the fermenter as it is fermenting is kind of like trying to measure how much lighter an elephant gets when it farts.

A long time ago there was a post on the HBD regarding using an air flow sensor to measure the amount of CO2 produced during fermentation and use that data to determine when fermentation was complete. It took a while, but I found the post and the page it linked here. Quite interesting stuff if you have the equipment.

 

[Gulf Brewery]

I had an idea for a device to keep track of how far through fermentation a beer was. To be honest, I have no plans to actually build this, but I'm interested in hearing what people think of it.
Does anyone see a problem with this idea (apart from being expensive)?

Mark

I have a microbrewery to test this at if you want to try your theory

You would have a rigid fermenter to cope with any shape changes when the fermenter is moved, shaken etc. Any small changes could put your calculations out by a long way. Also, you would have to cope with samples being removed from the vessel (everyone samples their worts while fermenting, don't they)

There are electronic SG sensors out there - not sure of the cost of them.

Chees
Pedro

PS - anyone want to balance 12hl of fermenting wort on a set of scales is welcome to try.

 

[mesa]

Cool idea Mark, (not that I'm really that interested in how fermentation is progressing most of the time, but cool gadgets ;-)

It got me thinking though, I wonder if you could do something similar by just counting bubbles in a simple s bend air lock. I mean an airlock should release a bubble whenever the difference in pressure between the inside and outside equals the weigh of water it has to move to let a bubble out. Except that in the airlocks most of us use once the bubble is released the water sloshes back and forth and you get some funky non linear dynamics going on. Maybe there are design parameters you could vary to damp the sloshing and get a release of gas which depends only on water depth, outside air pressure and head space on the fermenter. Then you'd just need to count the bubbles and calculate it all out ;-).

Thinking a bit more, maybe you don't even need to damp the sloshing but just get the statistics on mean time between bubbles and standard deviation of that time. Plug into a formula (empirical parameters determined from measuring a ferment with a hydrometer every hour ;-) along with water height and head space and get your total volume of CO2 released.

On the other hand maybe the error bars on these methods are astronomical ...

 

[newguy]

Just thought of another one. A bubble escaping from an airlock will jiggle it. An accelerometer (motion sensing chip) mounted right on the airlock could pick up this periodic jiggling and when it died down to a certain point, fermentation is reasonably close to complete. Not sure if a standard accelerometer would be sensitive enough to pick this up though.....

 

[Doogiechap]

PS - anyone want to balance 12hl of fermenting wort on a set of scales is welcome to try.

:icon_offtopic:
Bloke, I think Guest Lurker has something rigged up in his backyard that should do the trick :lol: .

 

[Zierschy]

There are electronic SG sensors out there - not sure of the cost of them.

http://www.coleparmer.com/catalog/product_...asp?sku=2575040

Ouch

 

[Gulf Brewery]

http://www.coleparmer.com/catalog/product_...asp?sku=2575040

Ouch

The RS232 option is bad enough, never mind the meter itself (I have even used one of them before - nice to use).
I think there is a standalone sensor out there as well somewhere - I did find it before with google

Cheers
Pedro

 

[chovain]

You would have a rigid fermenter to cope with any shape changes when the fermenter is moved, shaken etc. Any small changes could put your calculations out by a long way. Also, you would have to cope with samples being removed from the vessel (everyone samples their worts while fermenting, don't they)

I don't think either of these would be as big an issue as you might expect. Back of the envelope calc says there's 1.25kg of sugar in 25L of 1050 wort. Assume 75% of it is glucose, and that all the glucose ferments. Glucose is 180 g/mol, so you've got 5.2 mols to ferment. Basic fermentation gives 2 mol of CO2 for every mol of glucose (along with a mol of alcohol and a load of energy). So we expect to see 10.4 mol of CO2. At 44g/mol, we'll have about 450g of gas. CO2 has a density of 1.98 kg/cu.m at STP, so you're going to get over 200L of gas out of the fermenter. If you sample/distort 2.5 L of wort (that's a lot!), you're only going to create a 1% error (on the attenuation). The device will tell you you're 74.25% attenuated instead of 75% - that's well outside the accuracy of even expensive commercial equipment.

 

[barry2]

Hello Mark.
I like new gadgets.
From what I have read some brews,for various reasons,will still release some CO2 after fermentation is complete.

 

[chovain]

The biggest problem with measuring the weight of the fermenter has to do with the relatively small change in mass. Big changes are easy to pick up, but when the changes are small, things get much more difficult. 20l of 1.050 wort will weigh 21kg, and if the FG was 1.000 the beer will only lose 1kg.

It's worse than that: There's actually a good percentage of alcohol in your beer, which is significantly less dense than water (about 80% density). The SG of wort drops for two reasons: CO2 is released, and the wort expands. Only about half of the apparent 1kg loss is actually lost mass (See the calc in my post above). The other half is expansion from alcohol. Then you've got the problem that you're not just trying to see the difference between 21kg and 20.5kg: You're trying to tell the difference between 1014 and 1012: The mass difference between those figures for any given wort is going to be about 1g/L (remember, it'll also expand to make up the 2 point loss).

 

[Gulf Brewery]

I don't think either of these would be as big an issue as you might expect.

Ok, sorry didn't explain myself
If I move / distort etc the fermenter, I will drive CO2 out of the fermenter. I am not sure how much it will drive off / alter your figures etc.
I don't think that I will ever go for this method - but like your calculations. Keep going and lets see where you get to.


Cheers
Pedro

 

[chovain]

From what I have read some brews,for various reasons,will still release some CO2 after fermentation is complete.

I'm aware that dissolved CO2 can be released, but is there any other source of new CO2?

Temperature fluctuations will drop CO2 out of solution: That's easy, because we need to know the temperature for accurate gas measurements anyway, and can infer the amount of CO2 that has been dissolved, and the amount being released from the solubility changing.

Agitation drops CO2 out too, through nucleation, and is definitely more of a problem because I can't think of any way to account for it. Agitation will lead to the attenuation reading coming out a bit high, but if more CO2 is produced, then it'll be absorbed into the wort more easily, making the reading correct itself. If you agitate at the end of fermentation though, you'll get a slightly high attenuation, giving an FG reading that is lower than it should be.

The biggest worry I have about CO2 quantities is actually when the yeast is ramping up. Those baby yeast cells are surely going to need some carbon to grow up big and healthy. The glucose must be respired differently to give them their carbon building blocks, and I have no idea what effect that has on CO2 production.

Another worry I have is I don't know if yeast behaves like most organisms in the presence of oxygen. Most organisms create 6 mols of CO2 per mol of glucose instead of 2, but skip the alcohol production. That'd completely mess up my calculations, as you'd need to know how much oxygen was dissolved in the wort!

 

[chovain]

Ok, sorry didn't explain myself
If I move / distort etc the fermenter, I will drive CO2 out of the fermenter. I am not sure how much it will drive off / alter your figures etc.

I can think of two things you might mean by move/distort:

If you change the shape of the fermenter (by putting pressure on the side, for example), the amount of CO2 you drive off will be equal to the volume change in the fermenter times the pressure of the CO2. If you have wort sitting in a fermenter, which is right at the 23L mark on the side, and a pile of kegs falls against the side of the fermenter, you might expect to see the wort level rise to 24L (because the side of the fermenter has been pushed in). If the CO2 is at atmospheric pressure (it's probably be about 5-10% higher with my device), you're going to lose a 1L of CO2 - negligible compared to the 200L+ you're expecting.

If you disturb/shake the fermenter, you're going to get gas coming out of solution. As per my last point, I reckon that's a reasonably serious problem near the end of fermentation, but not a problem early on: new CO2 will be dissolved in the undercarbonated wort.

I just thought of a way of getting a good reading after you've shaken the fermenter: bring the temperature up a couple of degrees, and a normal batch will release a determinable quantity of CO2. A shaken batch won't release as much: again, I'm not sure how much of the dissolved CO2 gets released. For reference though, at 12 deg, there's 30L of CO2 dissolved in a 25L batch; at 22 deg, there should be 20L.

Another option might be to make sure the valves are not switched immediately after an increase in capture rate. Shaking will cause the pressure to increase quickly. Letting it sit without releasing the pressure will cause most of it to be reabsorbed (assuming constant temperature)

 

[redbeard]

Wont the different levels of dry / late hops used & trub produced make the weighing option not so good ?
Measuring gas is clever but what if it gets stuck ? You still need to do a hydro sample for the fg ...

Should you really measure the sugar or alcohol or both to measure fermentation progress & hence og/fg ?

 

[MHB]

How about a sight tube, fit a pressure transducer at the bottom

From P=Ro.g.h

We know g ~9.81
The hight we can measure
Rearrange to give Ro or the density.

Mark
I am sure you meant 2 Moles of Alcohol and 2 Moles of CO2, or the beer will be very hot indeed.

MHB

 

[chovain]

Wont the different levels of dry / late hops used & trub produced make the weighing option not so good ?

No, the weighing option will not be affected by solids, as they are made up of non-fermentables, which are there at the start, and there at the end. The total weight of the beer is only affected by the amount of CO2 has been released (c.f. specific gravity, which is a measure of both the wort mass and volume). The weighing approach, and gas-volume approaches are measuring exactly the same thing: quantity of gas released, hence amount of sugar fermented. They're just approaching it from different angles.

Measuring gas is clever but what if it gets stuck ? You still need to do a hydro sample for the fg ...

If you mean stuck fermentation, then that's okay - given the OG and the wort volume, the device can know the exact SG at any point in time (assuming my hypotheses about CO2 generation are correct). It could even have a warning light to tell you that the fermentation is stuck! Certainly no need to take an FG reading: I'm getting more confident that the device could tell you the change in gravity (OG - FG) much more accurately than a good hydrometer (although you'd still be basing the whole thing on an OG reading, so that's a moot point, really).

If you mean blow-over (krausen out the airlock), then you have a really good point. You'd need to make sure you didn't get krausen in it, or it would get bad measurements (the volume of the measurement vessel would change with krausen in it).

Should you really measure the sugar or alcohol or both to measure fermentation progress & hence og/fg ?

The most accurate way of measuring fermentation progress is through percentage of sugar fermented (real attenuation). One of the problems with hydrometers, and to a greater degree, refractometers, is they cannot directly tell how much sugar you've fermented by subtracting your FG from your OG. When you take a sample, you're measuring some combination of the sugar level and alcohol level: removal of sugar and production of alcohol both reduce the gravity.

If you take water, it'll come out at 1.000: you know there's no sugar in it, but not all 1.000 samples are sugar-free. If you make a 1.080 wine or mead, you know there's 80 grams of dissolved solids. When your wine hits 1.000, there is still a bit of sugar in there: just enough to balance out the lower-density alcohol.

Brewers before us came up with the concept of "apparent attenuation" to try and simplify everything. We pretend that it's the percentage sugar the yeast has fermented, but in actual fact, it's how much sugar it looks like if we pretend that alcohol is 25% heavier than it actually is.

When you get software to calculate your percentage alcohol for you, it's converting from apparent attenuation to "real attenuation" (a lower number, which you need to know both the apparent attenuation and OG to calculate), and multiplying by OG to get the amount of sugar that has been fermented. From that, it can work out how much alcohol is in there.

 

[redbeard]

so u really want a digital gas flow meter for $50 & some software ?

perhaps BB can design his conical with inbuilt load cells in the legs