Science Interviews

Interview

Sun, 7th Oct 2007

Kitchen Science - The Science of Scotch Part 2

Chris Forman, Cambridge University

Listen Now    Download as mp3 from the show Brewing and Alcohol

This is the second part of this week's Kitchen Science, you can find the first part here.

Ben -   Hello again, welcome back to kitchen science.  While I've been down at the pub, [to find out about the effect of alcohol on the liver] Chris has been keeping an eye on our distillation, and I can see that in the bottom of his pear shaped flask, he's actually collected a few milliliters of clear liquid.  Chris, what's happened while I've been away?A whisky safe

Chris -   Well you missed the exciting bubble moment, when all the beer frothed up, we've got a little pressure release valve so that wasn't a problem.  What's happened is the alcohol and water mixture has come out of the beer, condensed at the top, come down the tube and collected in this flask here.  We now have what should be almost pure alcohol in this glass.

Ben -   So can we take this out and have a closer look at it?

Chris -   We're not allowed to drink it, that would be very bad for you.  It's slightly yellowy, so that means that some of the products in the beer have come through as well as the alcohol itself, which is what you would expect.

Ben -   But it's no-where near the colour of the beer, so presumably the compounds that make up the colours in the beer have been left behind.

Chris -   The vast majority of them have, yes indeed.

Ben -   So what we have left is what could be very tasty but almost completely non-alcoholic beer.

Chris -   Well there would still be some alcohol in there, but a much smaller proportion, as most of the alcohol has come out into this flask.  In fact, if you kept the process going, what would happen is that different compounds would come out of the beer.  If we wanted to we could put another flask on, and collect another type of substance.  In the whisky distillation process, which is what we're looking at, it's very important that different stages of the distillation are siphoned off in different directions.  That is, indeed, the art of the whisky distiller - to control the flow of the fluid our of the barrel and into the final drink.  Incidentally, you cant call it whisky until it's been maturing in a barrel after the distillation process for three years.

Ben -   So if distillation is such a useful process for separating and purifying different chemicals, other than making strong alcoholic beverages, what else do we use it for?

Chris -   Well it's fantastically useful for all kinds of things, taking crude oil; distilling it into paraffin, into kerosene, into gasoline, all the different kinds of oil.  Desalinating salt water to get freshwater and salt.  Any sort of process where the boiling points of the liquids involved are more than about 10 degrees apart, you can use distillation to purify or identify individual compounds in a mixture of fluids.

Ben -   So it's a really useful process we can use to separate out all sorts of things and get the different products out of crude oil and that sort of thing, but how long has distillation been used?

Simple Distillation Set UpChris -   Distillation has been around for millennia.  Originally it was Babylonian alchemists in Mesopotamia, that's the first known set of distillation equipment, but it was refined into it's modern form by, of all people, a Muslim Arab in about 800AD.  In fact, the word alcohol itself is Arabic, and it means 'finely divided', which is very interesting.  Of course, the Arabs used it to make perfumes, rather than alcohol.

Ben -   Okay, so I have been down to the pub, and in the time that I've been away a little bit of liquid has collected in your pear shaped flask.  For all I know, that could be a bit of water that you've put in there, so is there any way that we can prove that is the alcohol distilled out of the beer?

A whisky safe Chris -   Well normally you would measure the specific gravity, and when they measure the specific gravity of whisky, customs and excise keep that section under lock and key, so that the brewery can't cheat and say that it's stronger than it really is.  What we can do today, because it's to small to measure the specific gravity, is to set fire to it, and if it burns that proves that it's flammable, and most likely to be ethanol.

Ben -   Brilliant.  Obviously this is something we should do somewhere safe, I guess?

Chris -   Of course, yeah.  I'd just like to point out that we have all been wearing safety spectacles and appropriate safety equipment and we should do the burning in a fume hood.

Ben -   Okay, well lets pour this liquid out into a beaker, take it to a fume hood and see if it lights... <The squeaky door of the fume hood opens> ...So we've come over to the fume hood now, and I see you're just pouring that into a beaker.  There's not a lot of liquid there, just a couple of milliliters.

Chris -   A very very small amount.

Ben -   Lets see if we can get this lit...   ...Oh!

Chris -    There was a flash, of blue.

Ben -   Well that was very brief, but there was clearly a flash of blue flame there, that did ignite.  So I guess this proves that you have distilled alcohol out of beer!

Chris -   That's correct, probably what we've got here is a slightly larger amount of water than we wanted, but a lot of the alcohol came out in one go.

Ben -   And that's all we have for kitchen science this week, but we will be back with more next week, so all that remains is to say thanks to Chris.

Chris -   Thank you!

Ben -   And goodbye...

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