A way to find alcohol percentage without even opening the fermenter!

[mew]

I just realized that mass and Fg (force of gravity) of the two waste products of alcohol fermentation are almost exactly equal (fiddle with the alcohol ferm. equation and molecular weights of CO2 and ethanol, you'll see). That means that the mass of the CO2 released during fermentation equals the mass of the ethanol in the container. By using the density of ethanol and the mass of the liquid inside the container, one could easily calculate the ABV of the liquid by weighing it before and after fermentation, without ever opening the fermenter! Blow off tubes would not be appropriate with this technique, and the scale would need to be a nice one that is accurate, if possible, to the gram. This method would also not be affected by temperature, another plus! I was exited when I thought of this because I like to brew many small batches and I don't like taking any beer out for hydrometer readings. Thought I'd share it with you guys even though other people have probably posted about it.

 

[Evan!]

Good thought...but finding a scale that can handle a full carboy, and is accurate down to the gram/ounce sounds much more difficult (and expensive!) than just buying a hydrometer.

 

[Sir Humpsalot]

Allow me to inject a bit of Rube Goldberg ingenuity into the mix...

Instead of needing a super-accurate scale, what if you mounted a bathroom scale upside down and put the carboy at the end of a long lever. So that each ounce of downforce at the carboy equals a pound of upforce at the scale?

Maybe you could even use a fishing-type scale with the pounds and kilos replaced by ABV. Just think... you could walk into your fermentation room, and just read the ABV directly off a scale on the wall...

 

[Evan!]

My next DIY project:

you drop the marble into the funnel, it travels down the tube, knocks the little foot, which kicks the block, which falls on the seesaw, which lights a match, which burns a string, which drops a weight, which launches a ball into a scale, which, finally...removes the bung from the carboy when you're ready to rack.

Jesus. With all the time you might spend building these elaborate contraptions, you could be brewing beer. And therein lies the real crime.

 

[Sir Humpsalot]

Dude. A lever, a piece of wood, and two eye-bolts. You could have the thing set up in under an hour. Calibrating it might take longer though.

 

[Orfy]

Yes but it fun to think about these things.

I don't think there's a brewer out there who doesn't like gadgets or building things.

I like the KISS philosophy.... Keep It Simple Stupid

But I still design and Build my own bits.

 

[mew]

That's pretty ingenius Toot!
It'd be fairly easy to calibrate by estimating the torque on the scale end of the lever arm using simple newtonian equations:
The sum of the torques in the y-direction = 0
T=(F)(R) F=(M)(g)

I'm going to try this! (I'm a gadget freak)

 

[Sir Humpsalot]

Thanks mew!

I would probably try something like a 5 pound fishing scale, since it would probably have the required accuracy.

Now, in order to balance out the weight of the carboy, you could use barbell weights, suspended underneath the scale.


Carboy...............................................fulcrum.........scale

50lbs.....................................................^...............100lbs of weight


then using a scale pulling up on the hundred pounds side, which should be roughly balanced by the carboy. Of course, you can use whatever kind of weights you have handy... bricks, stones, whatever, until you have about maybe 4 pounds indicated on the scale.

Then as the fermentation does its thing, the brew gets lighter and the scale goes down, indicating some percentage of alcohol.



Just curious... how many ounces(?) of change would there be in 5 gallons of wort?

 

[Orfy]

How long would the arm have to be and what about friction at the fulcrum?

 

[Sir Humpsalot]

How long would the arm have to be and what about friction at the fulcrum?

I would use something like sheet metal for the fulcrum. I mean, no hinges or anything like that. Or, tilt a piece of square-tube steel 45 degrees and use that. Use a metal plate on the bottom of the plank to minimize friction (wood on metal would tend to dig in). This ought to give you a very low-friction set up.

As for the length of the arm, I guess you'd have to know how much mass is lost in converting 5 gallons of beer into 5% ABV. Once we know that, we can figure out how long the fulcrum has to be, but generally, I would say that longer will yield more accurate results.

 

[david_42]

What you really care about is the change in weight, not the total weight. For 5 gallons at 6% w/w, that is on the order of 2.5 pounds.

Begin with a simple balance beam. Place your fermenter at one end and an equal weight at the other. Put a precision scale that can measure 2 Kg under the standard weight. As the brew ferments, the scale will give you the grams of CO2 lost.

Construction and calibration are left as an exercise for the student.

[If you use buckets, it could be as simple as three eyelets, a board and some string. And of course, something to hang it from.]

 

[mew]

We'd have to know the coefficient of friction to determine Ffr, but I think it's pretty much negligable because it the friction is acting on the point of rotation.

 

[Orfy]

I have a feeling that it would need to be so long that the flex in it would make inoperable.

I think there's a lot of head scratching and long sums to be done.
Good idea but I'll stick with my turkey baster and hydrometer.

 

[mew]

It wasn't necessarily meant to be implemented, but more to think about it. I do a lot of small batches that I'll try it with because a scale that measures that low a weight wouldn't be all that expensive. Good food for thought.

 

[Sir Humpsalot]

I have a feeling that it would need to be so long that the flex in it would make inoperable.

I think there's a lot of head scratching and long sums to be done.
Good idea but I'll stick with my turkey baster and hydrometer.

I don't think flex would matter much... because you'd still have a fulcrum. Sure, it'd be a TINY bit shorter, but you could account for that...

 

[boo boo]

All fine ideas, but I think I'll keep my fermenter in my fridge where it can't accidently be broken by levers and fulcrums and such.

 

[ajf]

I read the OP and though Bull****.
Then I did the math, and realized just how much CO2 was being generated.

I'll admit that my Bull**** thought was premature.

Could this excessive CO2 generation be responsible for the apparent suffocation of five of my wife's pet cats in the last four months in the vicinity of my fermenting room?

Then I realized the CO2 is a greenhouse gas, and that home brewing is a major contributor to global warming.

As a responsible person, I shall immediately stop any further brewing (until Sunday, when my next starter should be ready).

-a.

 

[Kaiser]

This method would also not be affected by temperature, another plus!

It is actually affected by the temerature since the temperature of the beer will determine the amount of CO2 that remains in the beer. But the change is not big enough to cause a substantial error though.

Another factor that can be accounted for is that 1g of extract is actually converted into 0.483g CO2, 0.462g alcohol and 0.053g yeast. For an average 5g batch that is about 100g yeast (~3oz).

Kai

 

[Vermicous]

I failed physics, so I may be thinking wrong. Couldn't you immerse the entire fermenter and measure the displacment before and after?

 

[Kaiser]

I failed physics, so I may be thinking wrong. Couldn't you immerse the entire fermenter and measure the displacment before and after?

I thought about this as well, by the error might be to large since the difference between before and after will only be a few 1/32 of an inch.

Another, actually practical method would be a precision flow meter that you attach in place on an airlock. This would measure the CO2 that escapes the fermenter and with some mathematics you can get a fairly precise gravity reading. If you could make one for less than $100, especially if it is coupled with a thermometer probe that goes into the beer, you shouldn't have a hard time selling this gadget. The only problem is, that you must not get any kraeusen into these instruments.

Kai

 

[mew]

It is actually affected by the temerature since the temperature of the beer will determine the amount of CO2 that remains in the beer. But the change is not big enough to cause a substantial error though.

Another factor that can be accounted for is that 1g of extract is actually converted into 0.483g CO2, 0.462g alcohol and 0.053g yeast. For an average 5g batch that is about 100g yeast (~3oz).

Kai

That's true, but it would be easy to account for. Just use the ratio of CO2 to ethanol instead of a 1:1 approximation. I hadn't thought of the conversion to yeast, but you're quite right; the yeast do grow in number and overall mass.

Also, displacement only measures volume, and the volume of the fermenter would not change regardless of what's inside it.

 

[Kaiser]

Also, displacement only measures volume, and the volume of the fermenter would not change regardless of what's inside it.

The volume wouldn't change, but its weight and with that the amount of displaced water. It's almost like an inverse hydrometer. You float the carboy in water and as CO2 is driven off it will float a little higher.

Kai

 

[mew]

Ahhh! I see. Thanks for the clarification.

 

[Sir Humpsalot]

It is actually affected by the temerature since the temperature of the beer will determine the amount of CO2 that remains in the beer. But the change is not big enough to cause a substantial error though.

Another factor that can be accounted for is that 1g of extract is actually converted into 0.483g CO2, 0.462g alcohol and 0.053g yeast. For an average 5g batch that is about 100g yeast (~3oz).

Kai

But lets assume you have a fish scale that read linearly. Sure, maybe you'd have more yeast production or whatever, but by comparing your early results to a hydrometer reading, you'd be able to take that into account when you create your overlay onto the scale which tells you the alcohol level.

In other words, I would think that it could wind up as a "hidden variable" that's there but is accounted for in such a way that it really doesn't matter. I'm quite intrigued by this. Did any of you math lovers figure out how much of a change in mass we are talking about here?

 

[Kaiser]

Did any of you math lovers figure out how much of a change in mass we are talking about here?

David already mentiond that it is about 2.5 lb which is about 6% of the initial batch's weight. If you have 1% error in your scale you can determine the current gravity with an error of about 16% which is actually not that bad.

Maybe something like that: http://www.davis.com/showpage.asp?L3ID=2633

could give you an error of less than 1%

Kai

 

[Kaiser]

David already mentiond that it is about 2.5 lb

If you think about it, two 5 gal batches produce as much CO2 as you get in your 5lb CO2 bottle used for kegging. That's why big brewries actually store the fermentation CO2 for further use in the brewery.

 

[the_bird]

Kai, did you just quote yourself?

 

[mew]

If you want a cheap way to get a weight accurate to the gram, a balance would be really easy to make. In order to use half as many gram or half gram weights you could cut the carboy-side lever arm in half.

Carboy.............^................................weights

 

[Kaiser]

Kai, did you just quote yourself?

Yes I did as I found it pretty interesting how much CO2 is actually produced.

Kai

 

[Sir Humpsalot]

If you want a cheap way to get a weight accurate to the gram, a balance would be really easy to make. In order to use half as many gram or half gram weights you could cut the carboy-side lever arm in half.

Carboy.............^................................weights

You are right, but the other issue is what range is your scale and how accurate do you want it to be? The further away you get the scale from the fulcrum, the more exaggerated the forces on it will be.