Using electronic scales for running gravity reading

[schrodinger]

BTW, because gas flow out of the fermenter (i.e., bubbling) is at steady state with CO2 addition to the headspace, which means the bubbling flow rate equals the rate of CO2 production. This means you don't have to measure CO2 concentration even during the first day, before the headspace becomes saturated with CO2.

There would be a small correction for the fact that the bubbles of CO2 emerging from the beer will also be saturated with water vapour (around 2.1% at 18C), so the CO2 production is really ~= 98% of the airlock bubbling rate.

 

[ekul]

Schrodinger, i think your calculations are wrong. For 106 moles of co2 to be produced you'd need 53 moles of glucose to be fermented out which is 180.16 x 53 = 9.55 kg glucose.

if malt malt extract is 55% (quick search, probably wrong) maltose (which is 2 glucose molecules stuck together) and you get 80% attenuation the 4kg of dme would yield 9.76 moles of glucose ---> 19.5mol co2.

ArgM. If you knew the profile of your extract or grain you could probably just measure the volume of gas that is produced. 1mole of co2 takes up 22.4L volume @ standard temp and pressure.

You could just have an accurate flowmeter on the airlock and use PV = nRT to work out what volume is being produced, ferment @ 20C and you can assume that each mole of is 22.4L

Either that or just measure the CO2 loss with scales. 19.5 mole of CO2 is ~860g, a decent set of scales would be able to measure this.


You will have to check the composition of your extract (whether it be grain or malt extract) but it should be fairly easy to work out and how much the CO2 dissolves into the liquid. You could take manual gravity readings and correlate this with the loss of CO2.

 

[MastersBrewery]

As stated in a previously linked thread tracking gravity by measuring CO2 output is accomplished more easily with a Mass flow controller and that some of these even calculate this volume for you. Obviously you'd need a starting gravity. Check the post by MalFet

 

[ArgM]

Yeah, Ive managed to find a DIY Mass flow controller project online I think Im going to have a shot at as well

Ekul, how would you check the composition of the extract?

 

[schrodinger]

Schrodinger, i think your calculations are wrong. For 106 moles of co2 to be produced you'd need 53 moles of glucose to be fermented out which is 180.16 x 53 = 9.55 kg glucose.

My calculation was internally correct but it was the wrong calculation!


Here was my calculation:

4 kg DME x (1000 g DME/1 kg DME) x (72 g C/180 g DME) x (1 mol CO2/12 g C) = 133 mol CO2

As long as DME is 100% carbohydrate (C6H12O2 in whatever form -- maltose, glucose, etc), it will have 72 g C per 180 g DME. DME will have some other solids besides carbs, but I believe it's still over 90% carbohydrate. So the fact that it's 55% maltose might not be relevant. I suppose it depends on the yeast, but I always thought that unfermentables reduced attenuation, so this is already captured in the 80% factor.


The total mass loss is the amount of CO2 produced by metabolising 3.2 kg of C6H12O2 (80% attenuation of 4 kg). First, find the mass of CO2 produced:

3.2 kg C6H12O2 x (72 kg C/180 kg DME) x (1 mol CO2/0.012 kg C) x (0.044 kg CO2/1 mol CO2) = 4.7 kg CO2


My mistake was forgetting that this is mostly anaerobic respiration, not aerobic respiration, so only one-third rather than 100% of the carbon leaves the system as CO2. So if you assume all the DME was consumed anaerobically, the correct answers are 44.4 mol CO2 and 1.56 kg CO2.

 

[schrodinger]

Yeah, Ive managed to find a DIY Mass flow controller project online I think Im going to have a shot at as well

Ekul, how would you check the composition of the extract?

You'll want a mass flow meter, not controller. The beer controls the rate of CO2 efflux.

 

[MastersBrewery]

You'll want a mass flow meter, not controller. The beer controls the rate of CO2 efflux.

no actually the controller as it allows a set volume to escape at a set rate, this will also allow you to pressurize the ferment if you choose to do so the meter will not

Ed:

Mass flow controller
From Wikipedia, the free encyclopedia




A mass flow controller


A mass flow controller (MFC) is a device used to measure and control the flow of fluids and gases. A mass flow controller is designed and calibrated to control a specific type of fluid or gas at a particular range of flow rates. The MFC can be given a setpoint from 0 to 100% of its full scale range but is typically operated in the 10 to 90% of full scale where the best accuracy is achieved. The device will then control the rate of flow to the given setpoint. MFCs can be either analog or digital, a digital flow controller is usually able to control more than one type of fluid or gas whereas an analog controller is limited to the fluid for which it was calibrated.
All mass flow controllers have an inlet port, an outlet port, a mass flow sensor and a proportional control valve. The MFC is fitted with a closed loop control system which is given an input signal by the operator (or an external circuit/computer) that it compares to the value from the mass flow sensor and adjusts the proportional valve accordingly to achieve the required flow. The flow rate is specified as a percentage of its calibrated full scale flow and is supplied to the MFC as a voltage signal.
Mass flow controllers require the supply gas to be within a specific pressure range. Low pressure will starve the MFC of gas and it may fail to achieve its setpoint. High pressure may cause erratic flow rates.

 

[schrodinger]

I know what a mass flow controller is, as I have a dozen or so in my laboratory. I don't know why you would want to pressurise the fermentation, particularly in a vessel that is not designed to withstand pressure, such as a glass or plastic carboy.

If you used an MFC for this application, there would be nothing to measure: you would be imposing the rate of CO2 loss rather than measuring it.

But go ahead and try it. Recommend you keep the kids away, as shards of glass from an exploding carboy will leave a mark.

 

[TheWiggman]

Refer topic - what happened to the scales man?
Or maybe get a fermenter set up with:

Scales
Mass flow meter
Ultrasonic sensor
Float on load cell

Calculate average, then confirm with hydrometer. Then realise the hydrometer works pretty well

 

[ArgM]

Thank god I have a plastic fermenter and no kids!

I dunno, scales didn't seem as useful as first imagined..
Hopefully will get them all running, I want to try and observe how everything interacts, no clue what I'll do with the information beyond that though!

 

[MastersBrewery]

I don't know why you would want to pressurise the fermentation, particularly in a vessel that is not designed to withstand pressure, such as a glass or plastic carboy.

Perhaps you should enlighten your self then, or you could try the duck nuts. I'm well sure no one is stupid enough to pressurise glass( seems comical a lab rat would make such a suggestion), I believe most Commercial breweries use Stainless and if you'd read the link the user on HBT using the mass flow controller was using a sanke keg.

 

[schrodinger]

The OP is using a plastic fermenter, as are the great majority of homebrewers.

 

[TheWiggman]

Masters, the flow controller that MalFet is quoting in the link also has a meter on it. Like schrodinger says a meter is required to measure the mass flow, not a controller. Maybe MalFet's idea was to have the controller to maintain a certain pressure in the fementer (albeit bugger all) to ensure air cannot get back in before or after fermentation. Or otherwise coupled with a keg to pressurise the fermentation, is a pretty funky concept. It would require a pressure sensor though for feedback, because unless you know the exact rate of CO2 production, you'll never be able to sustain a constant pressure.
The next iteration of the WW perhaps?

ArgM, I still think the scales are feasible. It would be a piece of piss to trial provided you have the scales, so why not give it a go?

 

[MastersBrewery]

MalFet was using a pressure transducer to read the pressure in the vessel and controlling that with the MFC, in either case a micro controller could easily do the math for you.

Ed: In any case it's a matter of how far down the rabbit hole one wants or dares to venture

 

[hotmelt]

This might do the trick

Take initial reading with hydrometer,add weight to float,set up dial gauge, connect to PC then mark SG at needle of start point.Simple

 

[TheWiggman]

Won't quite work hotmelt, the mass's force has to be equal to the float force. As soon as the SG drops the mass will fall.

 

[hotmelt]

I meant to change that to - add weights to counterweight to sink float below surface then set up dial gauge to zero - then as SG drops the mass would move gauge.I clicked post instead of back ,no time to change.

 

[TheWiggman]

I meant to change that to - add weights to counterweight to sink float below surface then set up dial gauge to zero - then as SG drops the mass would move gauge.I clicked post instead of back ,no time to change.

If I understand you correctly, that still won't work.
Once the float is below the surface it's buoyancy (which is relative to the fluid it's submersed in) will require a given force to hold it down. If it was under the water, then the downward force of the counterweight (mg) would have to be equal to that force as you've drawn it. So, once the SG of the wort increases, the float will require less force to hold it down; this will cause the counterweight to simply drop on the dial gauge. Well mostly, because the dial gauges have a spring in them to push the tip against the surface being measured. The spring isn't something I'd trust as reliable to do this role in this case.
For this example, you would be better to ditch the dial gauge and simply fix a spring to the ground and use the meter at the top to measure the SG. Again though, the choice of spring would have a huge bearing on it's performance for reasons I won't go into. Think F=kx^2 from high school physics.
As has been suggested above, measuring the force alone would be the best way to measure SG using buoyancy.

 

[TheWiggman]

This may be the solution you were after, albeit without scales -

http://brewnanny.com/brewnanny-base-model/

 

[ArgM]

Without watching the 20 min video, is there any where that describes how the BrewNanny works? Can't seem to find anything on the site that actually describes the product..

 

[dent]

Near as I can tell they release the CO2 at a certain measured pressure and attempt to use that release timing data to estimate your fermentation progress. Pulling a long bow with that I reckon.

 

[431neb]

I use a hydrometer.
And sleep in a bed with my wife.

Nah, just kiddding. Sounds interesting. I'll be interested to see if this goes anywhere.

You use a hydrometer on your wife when she sleeps in a bed?!!

Oh, my bad. As you were.

 

[MastersBrewery]

Near as I can tell they release the CO2 at a certain measured pressure and attempt to use that release timing data to estimate your fermentation progress. Pulling a long bow with that I reckon.

Actually probably accurate to 0.5 of a point, of course you would have to give it an accurate OG to begin with, CO2 correlates directly to the amount of alcohol produced/ sugars consumed by yeast. There is already a doodad on ebay that does the same thing, weirdly it allows the CO2 to inflate a balloon to a certain pressure and release it, counting how many times it is inflated and correlating this to gravity points lost. Obviously these measurements are all dependent on temperature and I note both have temp sensors on board. As long as you can measure temp, volume of CO2 produced, and have an OG, the rest is high school math, an R'PI wouldn't get warm doing the calculation.

 

[dent]

Yeah but,

• It relies on a very small pressure measurements in vessels of unknown materials - the flexibility will change the volume of the vessel with increase of pressure on some vessels, not much others
• The temperature changes the pressure/moles relationship
• The measurements are of very small quantities, and there are many measurements - maybe that improves it? not sure.
• The wort itself absorbs a certain amount of CO2, which relates to temperature and maybe the strength of the wort too?
• Wort fermentables are consumed during the yeast aerobic phase which does not generate much CO2
• Assumes perfect seal on the fermenter - how many air lock not bubbling threads are there?

I dunno, it seems like there are a lot of variables. Maybe they have gone to the trouble of controlling against all of them but I've seen plenty of prettily designed products which would work wonderfully if it wasn't for those pesky laws of physics.

I think CO2 measurement can be a great estimator of ferment progress, I just don't know about using it to get your actual gravity reading, at least in this setting.

 

[MastersBrewery]

I agree with a lot of your points, from what I understand brew nanny holds the fermenter at constant low positive pressure, it measures and controls the temp, so alot of the problems are as I said mathmatical. I'd agree with the ferment seal. Flexibility is insignificant with volumes of CO2 produce.

The advantage is without touching the fermenter you can see your within a few points of terminal gravity and if gravity is stable over days. Most of us wait (like I am ATM) 10-14 days take a sample and see where it's at, too high, leave it a few days, check again, ect ad-nausea. If I check at 14 days and I'm at terminal gravity, the question is how long has it been there, are my techniques effective, did it ferment out in 5 days create high fussel alcohols, then sit on lees for a week? I can't say. Some guys here use refractormeters to measure gravity they convert from Brix use an adjustment for alcohol and temp compensation to get an FG, how accurate a figure is the result of all that math?

End of the day being within a point or 2 so you can move to the next step is all that is really required. Still I'd be using keg lube to help ensure that fermenter sealed!

 

[ekul]

to measure co2 loss you could just weigh the fermenter, no need to measure the amount of gas coming off. Measuring the volume of the gas coming off would be inefficient as the volume would change as the temperature changes. However the weight of the co2 being lost will always be the same.

 

[TheWiggman]

to measure co2 loss you could just weigh the fermenter, no need to measure the amount of gas coming off. Measuring the volume of the gas coming off would be inefficient as the volume would change as the temperature changes. However the weight of the co2 being lost will always be the same.

Check out the thread title and head back to post #1. How much?

 

[MastersBrewery]

load sensor drift

 

[ekul]

well, say you make 23L of beer and its 5% abv. That means you have 1.15L of pure alcohol. density of alcohol is 789kg per cubic metre. 1000L to the cubic metre. 789/1000 x 1.15 = 907 grams of alcohol. Molar weight of alcohol is 46.07g So for a 5% brew you have 19.69 moles of alcohol.

For every 1 mole of alcohol produced you also produce 2 moles of CO2. Molar weight of CO2 is 44.01g.

If you make 19.69 moles of alcohol you make 39.38 moles of CO2. 39.38 moles of CO2 weighs 1733.11g

So for a 23L brew at 5% your weight difference should be 1.7kg. I'm drunk though so someone should probably check these figures.

edited to add~ You may need to check the solubility of CO2 gas in your liquid at a certain temps, however as a fully carbonated beer is 2.2volumes (or whatever) this should only equate to around 90g of co2. Wort is nowhere near fully carbonated though (obviously).

 

[TheWiggman]

well, say you make 23L of beer and its 5% abv. That means you have 1.15L of pure alcohol. density of alcohol is 789kg per cubic metre. 1000L to the cubic metre. 789/1000 x 1.15 = 907 grams of alcohol. Molar weight of alcohol is 46.07g So for a 5% brew you have 19.69 moles of alcohol.

For every 1 mole of alcohol produced you also produce 2 moles of CO2. Molar weight of CO2 is 44.01g.

If you make 19.69 moles of alcohol you make 39.38 moles of CO2. 39.38 moles of CO2 weighs 1733.11g

So for a 23L brew at 5% your weight difference should be 1.7kg. I'm drunk though so someone should probably check these figures.

Quiet Tuesday on the brews?
Bust out the scales ArgM. This is basically what you were asking for the whole time. How did it all descend into buoyancy, ultrasonics and CO2 measurement?