calculating abv

flanaganred

Hi was wondering how abv is calculated without knowing the SG or is it only possible in a lab with expensive equipment?

Khannie

There's a vinometer you can get, but it's not super-accurate AFAIK.

oblivious

flanaganred wrote: »

Hi was wondering how abv is calculated without knowing the SG or is it only possible in a lab with expensive equipment?

If you know the recipe and volume of beer, you could work out an approximate SG and use the following equation SG-OG/7.46 to get a ball park ABV value

rubadub

I think the vinometers are calibrated/suited to dry brews, fully fermented out.

Is there any reason you need to be precise? or just wondering about the theory of it.

flanaganred

rubadub wrote: »

I think the vinometers are calibrated/suited to dry brews, fully fermented out.

Is there any reason you need to be precise? or just wondering about the theory of it.

A neighbour made some cider with a variety of different apples only adding sugar and hoping the natural yeast would ferment it.I tasted a bottle and it was very sweet was trying to get an idea of abv as he took no SG and it did get me thinking what testing equipment was available other then a hydrometer

Ratsathome

Take a reading with your hydrometer now and take about 500ml of the cider and heat it to about 79C for 15 min so that the alcohol evaporate.Take another reading after it is cooled down.You will get your OG withing a few units.

oblivious

Ratsathome wrote: »

Take a reading with your hydrometer now and take about 500ml of the cider and heat it to about 79C for 15 min so that the alcohol evaporate.Take another reading after it is cooled down.You will get your OG withing a few units.

They will need to to up with distilled water to bring the original sample back to the staring volume, for a correct measurement

rubadub

The vinometer will not work well as you said it was sweet, you need to get the fizz out too

http://www.hambletonbard.com/how-to-make-wine-beer-moonshine-alcohol/wine-alcohol-meter-homebrew-vinometer.html

Remember: This meter will only work on normal home brew wines. If you check a liqueur, a sweet dessert wine or similar it will give you anything but the right value.

Ratsathome wrote: »

Take a reading with your hydrometer now and take about 500ml of the cider and heat it to about 79C for 15 min so that the alcohol evaporate.

Distillation doesn't work like that, wish it did!

oblivious

rubadub wrote: »

Distillation doesn't work like that, wish it did!

Its an old method from the mid 19th century developed for wine that alcohol will cause the same depression in SG as distilled water will. Its just something that you can use in a pinch

flanaganred

oblivious wrote: »

Its an old method from the mid 19th century developed for wine that alcohol will cause the same depression in SG as distilled water will. Its just something that you can use in a pinch

Will give it a shot for curiosity

rubadub

oblivious wrote: »

Its an old method from the mid 19th century developed for wine that alcohol will cause the same depression in SG as distilled water will.

Not sure what you mean here. Are you agreeing that heating wine to 79C for 15mins will remove all the alcohol?

It won't, its a common misconception, this myth is perpetuated by many ignorant TV chefs too, who often claim they have boiled off every scrap of alcohol. Look up any distillation site and it is usually in amongst all the other myths.

You would want to boil it for a good while until it has dropped in volume a significant amount.

oblivious

rubadub wrote: »

Not sure what you mean here. Are you agreeing that heating wine to 79C for 15mins will remove all the alcohol?

No

rubadub wrote: »

It won't, its a common misconception, this myth is perpetuated by many ignorant TV chefs too, who often claim they have boiled off every scrap of alcohol. Look up any distillation site and it is usually in amongst all the other myths.

You would want to boil it for a good while until it has dropped in volume a significant amount.

The original methods require boiling till a 50% reduction in volume, but its still just an educated guess

rubadub

oblivious wrote: »

The original methods require boiling till a 50% reduction in volume, but its still just an educated guess

That sounds reasonable.

An online calculator estimates if you have a 1L of 6% wash/cider and boil it till there is 500ml left then that 500ml left over will be reduced to 0.01%.

These calculators can throw out odd results for unusual requests, but it sounds reasonable.

Chimaera

With alcohol-water mixtures, heating them up vaporises both alcohol and water together. The amount of each in the vapour changes as you boil off more liquid. This image shows the relationship between alcohol content and boiling point:
.
At 79 *C you will remove some alcohol, but not as much as you'd think, and it gets harder as you lose more of it. (Of course, you could burn it off )

This is why separating them requires fractional distillation: each plate in the fractioning column separates them a little more until you get the desired separation at the top.

A quick look online suggests the main analytical technique used for quantifying ethanol content is GC-MS which very few homebrewers are likely to have access to I need to do a little research on other possible techniques that might be accessible to the homebrewer.

oblivious

Chimaera wrote: »

A quick look online suggests the main analytical technique used for quantifying ethanol content is GC-MS which very few homebrewers are likely to have access to .

Oh I wouldn't be to sure of that

rubadub

Chimaera wrote: »

At 79 *C you will remove some alcohol, but not as much as you'd think, and it gets harder as you lose more of it. (Of course, you could burn it off )

At 79C the cider/mixture will not be boiling though. Anything coming off will be simple evaporation, and it will be a mixture of alcohol & water evaporating off, not just alcohol.

The 79C figure comes about from the incorrect theory is that alcohol boils at around 78C and water at 100C, so if you heat to 79C it is wrongly believed that all of the alcohol will come off on its own. (this is the usual mistaken theory chefs will use to explain it too). Some are thinking of it sort of like a sieve, where the alcohol is like sand and the water like ping pong balls, and easily separated.

A fractional still will allow more water to be left behind, but there is no real need for this guys purposes. He need to just boil away until 50% or so is gone. This is also a lot easier as he does not need to control the power input to maintain the 79C suggested. The higher the power applied the faster it boils off.

If you want to use a thermometer in the experiment it would be to monitor the steam temperature, when it approaches 100C you know you have little or no alcohol left. Your thermometer will usually be off a little bit so as a test you can boil normal tap water first in your pot and measure the temp of the steam coming off it. You can put a lid on the pot so there is not much heat loss to the surrounding air, and the thermometer is being properly heated. You could also measure the temperature of the boiling liquid, but if its high in sugar I the boiling point changes, not sure by how much.

Carawaystick

Just hold a chilled plate over the steam and lick the condensate off your little finger.
Technically, to the letter of the law, this is illegal though, as you're distilling.

rubadub

If you do this boil off method I am wondering if a normal beer hydrometer will be able to show the difference. I don't think it will.

I have a spirit hydrometer myself as the regular ones were nowhere near accurate enough. i.e. I believe there is a small change in SG. While a hydrometer used for pre-brew & post-brew sugar solutions is in a relatively much higher range. Dunno if anybody has actually done it.