Science of Scotch: How whisky is made
In this special episode of The Naked Scientists, join Chris Smith on a journey from farm to whisky tumbler, as he witnesses the intricate processes behind producing high quality Scotch. Richard Broadbent leads a tour of Bairds Malt's site in Witham, explaining how British barley is prepared for its transformation into the delicious spirit, before Alistair McDonald of the Clydeside Distillery in Glasgow walks us through the five hundred year old craft of distilling malt whisky...
In this episode
00:44 - Malting barley to make the best whisky
Malting barley to make the best whisky
Richard Broadbent, Station Maltings
Making great whisky starts with the malting process, where the best quality barley is steeped in water to start it germinating, so it ramps up enzyme activity and beings to unlock the chemical energy stored in the barley seeds. Chris Smith met up with Richard Broadbent of Station Maltings in the nearby town of Witham, in Essex…
Richard - So we're heading down to our barley intake weighbridge area. Each lorry load of barley that comes to us will weigh around about 29 tonnes, and we have to carry out a number of quality analysis on each load that arrives on site before we tip it and accept it from the farmer. We keep around about 35,000 tonnes of stock at any given point. During harvest, we take in the majority and then we fill up our silos as as full as we can get them. And then as we use barley through the rest of the year, we refill them.
Chris - Now why barley? Why is that so special?
Richard - Barley is the perfect cereal for making whisky. Barley has a very strong husk, which protects the grain during our processing. It has a high amount of starch, protein and enzyme potential, all of which are important to the brewers and distillers later. And our climate is perfect in the UK for growing multi barley as well.
Chris - Where are we going now?
Richard - We'll head up to the barley weighbridge up here, and have a look at some of the barley that we brought in today.
Chris - Lead the way
Richard - So we're in our barley intake lab. So this is where we carry out all the quality analysis on the grain to make sure that the grain that we're seeing on our weighbridge is the grain that we've contracted from the farmer and to make sure that the grain is going to grow in our maltings when we actually get to the point of processing it at some point in the future.
Chris - When you drink a single malt, what goes into that, is it a huge great collection of different barleys that you've started with or do you work in a strict batch? This is one farm, one batch process.
Richard - We would contract with a number of our farmers. So around about this site we probably have about a hundred farmers. We contract certain varieties at certain quality parameters, and then we will bring those in at roughly the same time to then fill up some of the bins that you saw behind us. So we might fill up a 2000 tonne bin with maybe 20 farms of the same variety, the same quality parameters, and we will then process that bin for our customers thereafter.
Chris - So what happens now? You've got a batch of barley, you say it passes muster. What's the next step?
Richard - So after the intake process, we put the barley into our stores and then we recover the barley and make sure that the barley is going to grow when it gets actually into our steep tank. So in the UK we have a very light amount of dormancy in our grain. So it probably grows six or eight weeks after harvest, and then we'll take it to our steep tanks. And the steeping process is the first phase of the malting process. That's where we're going next.
Richard - It's going to be hot. Okay. We'll literally only be in there for a minute then. So we've come up to the first phase of the malting process, which is steeping, which is where we take our raw barley and we add moisture, which initiates the biochemical processes within the grain.
Chris - That's germination, isn't it? You're starting it growing.
Richard - Exactly, so the barley grain is effectively a seed that we are commencing the germination phase of. Each and every one of the millions and billions of seeds in every batch that we make. So we need to add moisture and the steeping process is how we do that.
Chris - Why do you need to germinate it? What does that do that is useful to yielding and releasing what's locked up in that seed?
Richard - The barley grain is starch globules covered in protein. And there is some enzyme there, but it's very low levels. And what we do in the steeping process is hydrate the endosperm. We initiate all the enzyme potential and increase those enzymes and then those enzymes will then break down the protein and they will break down the cell material. So at the end of germination, we have got a much smaller level of proteins. The starch is there, but it's now released from its bound protein matrix that it was in as barley. And the enzymes are all around about the starch. And at that point we put it in our kiln, which is effectively a big oven, to then dry it down and fix that enzymic protein and starch mix that we have created.
Chris - I think I need to grow a bit to see into these tanks, but they're enormous. They must be about four or five metres across these big circular tanks and I can see damp grain in there.
Richard - Yeah, so this batch has been in here for roughly 24 hours. We steep in a new batch every day and this batch will be in these tanks for two days. So we've got another set of steep tanks just through the wall there as well.
Chris - I can see water dribbling into one of the tanks next to us. So basically you put 28ish tonnes or whatever of barley in there and then half fill it up to just soak the grain and then drain that off. And you just repeat that a few times, do you?
Richard - Yes. So we repeat that one more time. So there's the first immersion where we put the grain in and then we fill the water to just above the grain bed so that all of the grain is homogeneously covered in water. And then we rise it a bit to make sure, again, that it's all well mixed. And then that first wet phase might be six or eight hours and then we'll drain it off. And then that's an air rest for, it could be 10 hours. And then we'll again fill the tank with water above the green bed for maybe another six or eight hours. And that second immersion should take the moisture level from the initial starting point of 12% up to say 44% moisture. And then there's a small air rest at the end until it's ready to move to germination. So we'll go to one of the four germination vessels that we have on site.
Chris - Hopefully it's a bit warmer because it's a bit chilly in here.
Richard - It's definitely warmer.
Chris - They're tall, those tanks, aren't they? Because we've just come down all the stairs that correspond to how tall they would've been. So they're quite big.
Richard - Yeah. So I think the green bed is around about three metres deep in those tanks.
Chris - And the conveyors will bring what we were just watching once it's had its immersions, they'll bring it over here.
Richard - Yeah. So they'll take the fully steeped grain. Damp barley effectively that started its germination process. So it's 170 tonnes of that grain along the rubber conveying belts that you can see behind us into the vessel. And we'll load this vessel in about three hours and then we'll look after it in here for four days.
10:16 - Distillery ready: germinating and kilning barley
Distillery ready: germinating and kilning barley
Richard Broadbent, Bairds Malt
Keeping the conditions just right is the challenge for malting barley in the quantities processed at Station Maltings...
Chris - Oh my goodness. You weren't wrong, were you, when you said it'll be warmer in here. It's like a hurricane force wind of hot damp air coming out the door.
Richard - Yeah, so we maintain the temperature level in here around about 16 degrees centigrade air on, and maybe 18 or 19 degrees centigrade air off. So hence the nice warm feeling that we got coming through the door.
Chris - This is a bit like the ring in a circus. It's that sort of size, isn't it? The floor is a whole heap of barley and you have a device that effectively stirs it and spreads it out as though you are spreading sand around the floor of your circus ring. And how often do you turn it over then to mix it up?
Richard - So this turning machine that you can see in front of us actually moves very slowly. It takes around about three hours to get a full circumference of the vessel. So we make sure that we keep the vessel turned a couple of times a day anyway. And that keeps the rootlets from matting together. It allows the air that you can feel coming past us to evenly flow through the bed. And effectively what we're doing is replacing the air, which is around about the grain. So it's respiring, it's taking in oxygen and producing CO2 much as we would. So we are using large amounts of air to replace the oxygen and also control the temperature to the setpoint temperatures that we're after.
Chris - How long will it stay in here?
Richard - So we germinate and heat these vessels for four days. And that is the perfect amount of time to break down the proteins as we need to and generate enough of the enzymes for our customers to use in their process later on.
Chris - And then where next?
Richard - So from this germination vessel, we'll go to the kiln. It's going to be very hot
Chris - Good grief. Not even in there yet. You have to pay a fortune in Finland for an experience like this, you know, Richard. Good grief!
Richard - We don't take tourists in here, for sure.
Chris - How is the heat produced? Is this gas or electricity?
Richard - Currently this is gas.
Chris - It's incredibly hot. I mean that's sauna temperature. That's really, really hot. What's your gas bill like?
Richard - It's huge. Yes, it's absolutely huge.
Chris - The current economic climate must have made that even trickier.
Richard - Yes, it has. It's made our products more expensive. It's made the beer that everybody buys in the pub or the supermarket, it has made that more expensive and it's made the whisky, which is being laid down for the future, more expensive as well.
Chris - For people who didn't get to experience the sauna. It looked pretty similar to where we just were, except that it was 9 million degrees. It was really, really hot. But it's basically the same thing. You've got a thinner bed of malt and you're turning that for a period of time and you're just drying it out. So how long will it spend in there doing that?
Richard - Our heating process, our burn process, is about 19 hours. And then there's the filling and emptying as well. And that allows us to take the moisture maybe from about 40% going in, reduce the moisture level down, and then start to build the temperature up towards the end of the process, which we just felt there just now. And those latter stages, they start to create the flavour and colour compounds and also fix the enzyme potential. Holds those enzymes in stasis for the onward processing at brewing or distilling phase.
Chris - So despite the extreme heat in there, the enzymes in the grains do remain viable and intact. And when they go to the brewery or the distillery, they will reactivate, reanimate, and start to break down the seed.
Richard - It's absolutely imperative that we give the brewer and distiller a high degree of enzymes as well as the starch, which we're giving them. So the brewer needs the starch to then convert into sugar. But to convert it into sugar, it needs the enzyme. So we need to give them a high level of enzymes as well. And of course, once the brewer, say, has converted their starch into sugar with the enzymes, that's when the yeast can then utilise the sugar to convert into alcohol.
Chris - Where does it go next after it's been dried?
Richard - So we put it into our storage facility where we take a sample and we analyse it in our central laboratory in Arbroath. When we have a full set of analysis, we can then determine that it meets our customer specifications and we can then set it for delivery to one of our many customers from this site, either in the UK or abroad, along the lines of their schedule.
Chris - And then next stop for stuff that comes out of here is your home hunting ground where you hail from. And that's going to be Scotland and the whisky industry.
Richard - Yes, exactly. So the whisky distilling industry requires a very high quantity of malted products each year. Largely distilling malt, plain distilling malt, and a little bit of peated malt, which we produce for our customers in Scotland.
Chris - Well, I've had a blast. It's been amazing to see this. And I started by saying I've stood outside this plant on that railway station and looked up at this for so many years and wondered what goes on here. And now I know.
Richard - Well, I'm very pleased to be able to show you and allow your listeners to hear about what we do. You know, people don't really understand what it takes to get a pint of beer on the bar or a bottle of whisky on the shelf.
Chris - Are you a Burns Night man?
Richard - I definitely am. Yes. I'm going to a Burns supper in the outskirts of Edinburgh.
Chris - Do you get some freebies? Will you be able to turn up with a decent bottle of stuff?
Richard - Sadly, we don't get too many freebies from our customers, so, no. No, sadly not
16:08 - How to make great whisky: Milling, mashing and fermenting
How to make great whisky: Milling, mashing and fermenting
Alistair McDonald, The Clydeside Distillery
Thanks to Richard, we’re now familiar with how the best quality barley is prepared for turning into the best quality whisky. But now it’s time to find out how the magic really happens. I’ve been to visit Alistair McDonald who manages the Clydeside Distillery in Glasgow to taste this most Scottish of tipples…
Alistair - Alistair McDonald. I'm the distillery manager here at the Clydeside Distillery in Glasgow, and I'm responsible for all things production and health and safety for the site.
Chris - Brilliant. Right. Take us on our way. Off we go.
Alistair - So this is us going into the first part of the production process, the mill room.
Chris - I've obviously seen the malting process. That's what I was doing down in Essex. Where do you get the grain from here?
Alistair - At Clydeside, we have four farms that grow for us here, and these guys supply barley to the maltings. But the important part for us at Clydeside is that it's all Scottish barley.
Chris - Does it have to be Scottish in order for it to be Scotch?
Alistair - No, it doesn't legally have to be Scottish to be called Scotch whisky, but we have years of experience using different types of barley. We used to import barley from farms abroad that weren't of the quality of Scottish barley. So quality is the most important. This is malted barley that's come from the farm. It's gone through the malting process that you've seen. It contains starch, and to expose the starch, what we have to do is drop it down through a four-roller mill. It all becomes combined. The malted barley goes through the mill, and it comes out as grist. Grist has a ratio, and we set up the mill to achieve 70% middles or grits, 20% husks—which is the outer casing of the barley—and then 10% flour. We feel that's the optimum ratio to help the conversion of starch into sugar in the next part of the process: the mashing.
Chris - I've always wondered where the term 'grist to the mill' came from. Now I've actually seen it in the flesh.The other thing I was surprised by—so you mill it down, and all of the stuff, all of the husk and everything, is going into the process. You're not separating it out, like if we were making flour for bread, we'd keep the starch and throw away the hard bits. You keep the lot.
Alistair - Yeah, it all ends up in the mash itself. The difference here is that when it comes through the mill, the top rollers of the mill basically do a rough grind, and it throws the outer case—the husk—over the top of the roller. The husk is important for drainage. If you can see the size of the husk, the particles of the husk allow the sugary liquid we're converting to drain out through the mash.
Chris - How big is each batch that you run, then, and where does it go next?
Alistair - It's a one-and-a-half-ton batch. Once we've run this through the mill—it takes about two hours to run it through—it's transferred into the grist bin, which gets it ready for the next part of the process: the mashing process. So that's where we're going next.
Chris - Let's do it.
Alistair - And here we are at the mash tun. You can see this vessel with the copper top on it. This is where the next part of the process starts.
Chris - It's a massive tank. There's a window in the front where we can look inside and see what's going on. There's a big pipe coming in from above—is that how you load it with the material we saw being milled?
Alistair - Yes, the one-and-a-half tons that we've just milled sits in this tank above the mash tun. We gravity-feed that grist down into the mash tun at the same time as adding hot water. The two mix into a solution, and what's important to us is that the grist comes in at a certain flow rate along with water at a specific temperature. That strike temperature is important for converting the starch into sugar.
Chris - One-and-a-half tons of grist—the starting material—how much water?
Alistair - It's 5,900 litres for the first water.
Chris - Water's really important, isn't it? Where do you get yours? Not out of the Clyde out the
window, presumably—that looks a bit dirty.
Alistair - No, definitely not from the River Clyde. It's actually from a loch called Loch Katrine. It's about 30 to 40 miles from here and is good Scottish soft water. In fact, it's Glasgow's town water, so it's high-quality Scottish soft water, which is important for whisky distilling.
Chris - So, in the tun in front of us, we've got that one-and-a-half tons of grist. You're beginning to add nearly 6,000 litres of Glasgow tap water, and it's slowly being turned and mixed. What's actually happening in there, then?
Alistair - The conversion of starch into sugar happens through chemistry. It's enzymes breaking down the starches into sugars. The sugar solution is called wort in the industry. We pump the wort into the washback, and what we're left with is some remaining sugars in the bottom of this mash. To reclaim the last of these sugars, we use water at a higher temperature. At Clydeside, we aim to create a clear wort, which looks like a pilsner or lager as it moves through the pipes before fermentation. We find that works well for the flavour profile we're looking for in this Lowland-style single malt whisky.
Chris - Now tell us about the yeast side of it as we walk to where you’re pumping this stuff to. The tun we were just seeing—the material that’s in there, the liquid—has now been piped over to one of these enormous... I mean, these are huge, great tanks.
Alistair - Yeah, you’re right. That’s seven and a half thousand litres of stainless steel tanks. We pump the sugary liquid from the mash tun across into this vessel. We put it through a heat exchanger and cool it down to 36 degrees initially for the first 200 litres. The reason we do that is to rehydrate the yeast, and we have to do that at a slightly higher temperature. It just shocks the preservative coating on the yeast and allows the yeast to start taking in oxygen. If we were to leave it at 36 degrees, it would have a negative effect—it would kill all the yeast, and we wouldn’t have any conversion of sugar into alcohol. So we have to then start reducing the temperature as we’re filling it. The temperature goes from 36 degrees right down to probably about 19 degrees. As long as we’re below 20 degrees Celsius.
Chris - How long will it spend in that tank undergoing that fermentation, then?
Alistair - Again, it’s down to personal taste and flavour profiles. Here at Clydeside, we actually do a 72-hour fermentation. We feel as though that’s the optimum. The alcohol tends to stop being produced around the 48-hour mark, but we feel that from a flavour point of view, 72 hours works very well for us.
Chris - What does it look like at that stage, then? Is it a bit like a kind of beer, effectively?
Alistair - You could call it a rough beer. It doesn’t look like a beer, but if you were to filter off the yeast sediment and the solids from it, yeah, it just becomes like a clear, rough, malty beer.
Chris - Good?
Alistair - It’s an acquired taste. It’s not one I would sit down at home with myself, but it can be drunk, yeah.
Chris - And how much alcohol’s in that by the end of that fermentation? What have you got it to?
Alistair - At the end of the fermentation, you’re up to 8.4%, 8.5%. I know we’re joking about rough beer, but we call it fermented wash—that’s the correct terminology. What we’re doing now is taking the fermented wash to our copper pot still. We want to boil it up, capture, and concentrate the alcohol more. So let’s make our way to the still house where this happens.
22:30 - How to distil and cask high quality whisky
How to distil and cask high quality whisky
Alistair McDonald, The Clydeside Distillery
The last part of the whisky making process is concentrating the fermented wash into the final blend, ready for casking...
Chris - Wow. You’ve got the best view in Scotland, I reckon.
Alistair - Yeah, it’s a still house with a view, isn’t it? You’ve got this glass box around the still that gives it a kind of greenhouse effect. The guys in production have got the best office in the city at the moment.
Chris - They sure have. Before we talk about these two enormous stills in front of us, can you just tell us a bit about the history of this building and where we are? How did you come to be literally on the dockside of the Clyde in the middle of Glasgow?
Alistair - Yeah, so the building to the right of us here is actually an old pump house. It’s a hydraulic water pump, and its job was to open and close a hydraulic bridge, basically allowing access for ships exporting all over the world. We had the Queen’s Dock that opened in 1877, and probably a lot of the exports from the city—and whisky being one of these main exports—were being controlled by this very building that we’re standing in at the moment.
Chris - We’ve admired the view, but the dominant feature in this... I want to call it a room, but it’s like a giant conservatory, tens of metres tall, with these two enormous copper stills.
Alistair - Yeah. So this is where the distillation process happens. The fermented wash that we spoke about in the tun room and the fermentation washback gets pumped through into this big copper still. This is just like a big copper kettle, and it’s got a heating element in the bottom. If you try to describe the shape, it’s an onion-shaped still, and halfway up the neck of the onion is a sight glass. You can see the liquid dancing in the window there, boiling away. What we’re doing is capturing the vapours coming off the top of the still, through the swan neck, and condensing them back into an alcohol liquid—a distillate. This runs into this brass box you see in the middle of the still house, which we call the spirit safe. The spirit safe is important because it allows you to see the liquid running, the rate it’s running at, and also to sample the alcohol strength and temperature of the spirit, which is very important to us.
Chris - What about the stuff that we don’t want to come across? There must be some bits of yeast in there, and also, are there any chemicals that you don’t want to distil across? How do you get rid of those so that you just get good quality spirit?
Alistair - Yeah. Firstly, on the solids—you’ve got the yeast, the dead yeast cells, and some fines that may have come through from the mashing process. But as you can see, the liquid is only halfway up the neck of the still as it’s boiling, so no solids are getting above that. Only the vapours come off the top, moving onto the spirit distillation. All the spirit you collect from the wash still gets pumped into the next still, which looks similar. The difference is you’ll see there’s a ball in the middle of this one—a copper ball. What we’re doing here is boiling up using the exact same process, but this time there are some unwanted characteristics and flavour compounds we want to discard. This happens at the early stages of the still. We discard that back into the previous tank for the first 15 minutes. We call this term the ‘foreshots.’ After the foreshots, we start collecting a new-make spirit at a strength of 76.5% alcohol. Here at Clydeside, we’re trying to create a delicate, clean new-make character. So from 76.5% down to 71%, that’s our final new-make spirit, which goes into what we call the ISR—the Intermediate Spirit Receiver. Then it’s pumped to the filling store for tanking offsite.
Chris - You distil it once, collect everything, and then put what you collect into the next distillation tank and distil it again. But you put back the first 15 minutes of what comes off into that tank so that you don’t get those characteristics going into the final blend. And what comes off that second distillation is that 76% down to 71% alcohol, which is going to become the final product.
Alistair - Yeah, that’s correct. And it’s not just the distillation part of the process—it’s all parts. You’ve got the mashing, you’ve got the clear worts, you’ve got the dried yeast, the type of yeast... There are a lot of variables in there that contribute to the final whisky.
Chris - And presumably the stage we haven’t yet discussed, which is that it leaves here and goes into casks. Tell us about that.
Alistair - It looks like the most boring part of the process, to be honest—the casks sitting in a warehouse for most of their life. But I would say in the region of 70% of the flavour of all whiskies comes at this part of the process. So you can do all the mashing, fermentation, and distillation, but depending on the quality of the wood—and it’s all about the wood—what’s it been used for? Has it been sherry? Has it been wine? Has it been bourbon? The time you store it... There are a lot of reactions going on.
Chris - These are second-hand casks. What’s been in those casks before is an informed judgement that will influence, or directly lead to, a characteristic in the product.
Alistair - Yes, we predominantly use bourbon casks here.
Chris - Are you going to show me some of the product?
Alistair - Absolutely, yeah. That’s the best part of today—getting the chance to go and have a nose and taste some of the final matured whiskies. Okay, so this is the new-make spirit. You can see it’s crystal clear—no colour whatsoever. This is the spirit that’s just come off the still, reduced to 63.5% and ready to go into the cask. But this is your chance to try the new-make spirit. It’s totally clear; it looks like water.
Chris - I would say that it looks like gin, doesn’t it? Let me have a sniff of it. Yeah, I mean, it smells like the classroom or lab ethanol bottle. Okay, I’m going to try it... There’s a lot of flavour to it. You can taste the barley.
Alistair - You get a kind of malt-biscuity note at the beginning, but once you get into it, you start to get more of the fruity flavours from the fermentation. So you’ve got more of a tropical fruit profile. Add a touch of water to it as well.
Chris - Is that what one is supposed to do with whisky? Because there seem to be mixed views on whether or not one should add water.
Alistair - Drink it how you like it, is the answer to that. The industry rule of thumb is that if it’s a cask-strength whisky, a touch of water takes that sharpness, that burning edge off and opens up the flavours. So, you’ve tried the new-make spirit. Now let’s move on to something a wee bit more enjoyable, I suppose.
Chris - This is now going to have the characteristic of the cask effect in it, isn’t it? Because this has been in a cask for a period of time. So whatever was in there before has now been imparted to it. Is this from a bourbon cask, then? Because it’s quite pale.
Alistair - This is actually our first release, and it’s from two casks, believe it or not—a bourbon cask and a sherry cask.
Chris - This is very smooth. The other one was quite powerful—obviously it was a lot stronger—but this is very, very smooth. It’s sort of velvety, slides around your mouth, and it’s very soft and delicate.
Alistair - Yeah, it has a really nice delicate mouthfeel and a nice oiliness. This has been aged just over five years, reduced from 63.5% down to 46%.
Chris - So you age it at high strength and then dilute it. You don’t dilute it and then start the ageing in the casks?
Alistair - No, we dilute it down to 63.5%. That’s the industry standard, which is higher than the bottle strength, as you rightly say, and we mature it at that strength. The reason you don’t go lower is that year on year, you’re losing alcohol strength, and you don’t want to get down below 40%.
Chris - Do you know what amazed me? When I read about the fraction of food and drink exports from the UK that Scotch makes up as a proportion of the industry, it’s a huge share. It’s more than a fifth, isn’t it, of our exports?
Alistair - Yeah, I believe so. I don’t know the current figures today, but recently, single malt whisky made up 25% of all food and drink exports from the UK.
Chris - Well, I’ve got to hand it to you, Alistair—thank you so much. I’ve learned so much from you in the last hour or so of looking at this process. I thought I knew basically what went into this, but I had no idea. So thank you for giving me the insights and for showing me the product going from grains of malted barley to emerging as something that’s firewater, and then with the cask, it tastes delicious. It’s been a real treat—thank you.
Alistair - It’s been a pleasure to take you through a quick journey of the processes. Thank you very much for your time, and hopefully your listeners will come and see us here the next time they’re in Glasgow to enjoy the same experience you’ve had.
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