Now let's talk now about some model experiments that were done when in my early days at UC Davis. This work was done by a chap called Greg Cap. What I charge Greg with was the the task of comparing the foam properties of the hordeins and the albumins. We have talked about these a little earlier. Remember the albumins are water soluble and the hordeins not very water soluble. But there is a heck of a lot more hordeins than there is albumin. There is more abundant hordeins and there is albumin. How important is that? Remember that the albumins contain the lipid transfer protein and the protein Z. What I asked him to do was to do this using model systems to pull out the albumins and pull out the hordeins from barley and compare them. Now if you are doing that, if you do not have a carbonated beers in my lab, you have got to have some way of comparing different solutions for their foam stability. What Greg devised is a shaking technique. He had a tube and you put your solution of protein in there, whether it is albumin or protein or whatever it is, and you shake it 10 times. Fifteen in-charge, that's the distance he was moving through. Within three seconds doing this, so you are generating the foam. You are nucleating the foam. Then you let it stand for about 30 min, and then you measure the depth of the foam. The deeper the foam, the more is the foam stability. This is a very simple way of comparing solutions for the amount of foam potentials. Now, here we are comparing the albumins A with the hordeins and we're comparing them after denaturation. What Greg did was denature the proteins, in other words, unfold them in two ways. He either used acid or he heated them. You can see that if you take the albumin or you take the hordein, if you denature them, you improve the foam stability. Now actually, what he found was those albumins were better at stabilizing foam than the hordeins. That is a very important observation. If you measure the hydrophobicity, let's not get hung up on how we did that, but you see that as you denature, you increase the hydrophobicity. What Greg did was to mimic what happens during malting. If you take barley, of course, the first stage commercial is to malt it, to steep it, and to germinate it. When you germinate, you develop enzymes, so-called proteases that chew up the hordein and dissolve more of the hordein. Now, the last count, and Hitchhiker's Guide to the Galaxy lovers will appreciate this. At the last count, there are 42 different proteinases in malt. It's very complicated. What Greg used was model enzymes and in particularly in this experiment here, he used ficin, which comes from figs. If you look at albumin and you treat the albumin solution with ficin over a period of 125 minutes, not a lot happens. If you take hordein right at the start, it is not got very good foam stability. But if you partially hydrolyze it for a minute or five minutes, the foam stability gets better. That is probably because you are taking these big, relatively insoluble hordein molecules, chopping them up and releasing smaller proteins that have got hydrophobic character, and therefore, they are able to stabilize the foam. But if you go too far, you will start to break them down and make them too small. Now this particular experiment was with an enzyme, a proteinase isolated from yeast. It's actually called proteinase A. You can see that neither albumin nor hordein like proteinase A. It seriously decreases the foam stability from the albumins. That data point at 114 hours for a hordein and is a genuine one, it ain't there. There is no foam stability. Brewing yeast produces enzymes that damage the proteins that stabilize the foam. I will come back to that point later on in the course. Now here is another student. This was Christian Melanie. The point I made to Christian was, Greg's done some great work, but of course, he used the proteins in isolation, hordeins, albumins. In beer they are all altogether. You have got hydrolyzed albumins and you got hydrolyzed hordeins all present in the beer. They competing or are they? What I asked him to do is to look at the foam stability of mixtures of these protein types. Now along the y-axis here, you have got the foam stability, the foam height. Along the x-axis, you have got increasing amounts of albumin. We did this at a series of fixed concentrations of hydrolyzed hordein. Let me walk you through it. If you look at zero on the left-hand side, zero is where there is no albumin. Therefore, if you add just no albumin in this solution, there will be no foam stability. If you look at the black squares. Now, we've got a fixed concentration of hydrolyzed hordein, naught 0.25. The figure you get at zero albumin, the foam stability is the foam stability due to hordein, Christian kept back constant, and added increasing amounts of albumin and you can see that the full stability increased. Now, it took another job you like, and he double the amount of hydrolyzed hordein, now 0.5. Now the foam stability is twice what it was at naught 0.25. That's the foam stability due to the hordein. But if you kept that constant, and you added more albumin, the foam stability does not go up as much, as it does at the lower hordein level, and so on to even higher levels of hordein, the albumin can't improve the foam stability. What's the explanation to this? The analogy, I always think is goalkeeper analogy, because I always bring things back to goalkeepers, that's what I wanted to be when I was a kid. I wanted to be the Wolverhampton Wanderers goalkeeper. Imagine many of you, you're going to be young and fit. Imagine me not so much, but I'm probably a very much better goalkeeper than you are, and it was a race to get into the goal. The first person to get to the goal and take that position would be you, and when you get there you're not very good. I would lumber in there, but if I managed to get that'd be a far better goalkeeper. Teasing, by the way, some of you may have played for your country. I'm just making a point here. It's a competition, hydrolyzed hordein is you, and hydrolyze albumin, is me. I'm actually better at foam stability, but hordein gets into the foam more readily. When it gets there it's not as good, it's more foamable, and it squeezes out the better albumins. Probably yes, lipid transport protein and protein Z, probably are better inherent foam stabilizing materials, but they are competed with by hordein. Now, this is something that the brewing industry are aware of now, but practically what do you do about it? Because you're going to have hydrolyzed hordein in there. But you got to be mindful of the fact that potentially if you minimize the amount of hordein that's present, then the foam stability pro rata, as long as you've got enough albumin, is going to be better. Hops. We're all familiar with resins and hops, the main resin and hops, alpha acid, of course, converted during boiling or chemically in a factory into iso-Alpha acids, and these improve foam stability. The reason is, they're hydrophobic, they got hydrophobic nature. Look at those side chains, those are hydrophobic, those are water-hating, which means that bitter substances are not that soluble. This is a model that was developed by Paul Hughes and Bill Simpson working at the Brewing Research Foundation or BRF International, was either become, a number of years ago, you've got the hydrophobic polypeptides or proteins, and they're linked together, the hydrophobic parts of the bitter acids, associate with the hydrophobic polypeptides, and then you've got a metal ion, that is bridging those iso-Alpha acids because they release hydrogen ions, they become negative. The important thing is, they have a slight negative charge, so if you have positive charge, you will link them together. Now, this is the part of what happens in beer, that is the least well-understood for foam. The nature of what those ions are. Magnesium trace and magnesium probably, and so on and so forth. But there has been a history of people putting in metal ion to improve foam stability. In Belgium, I don't think they're doing it so much now, but there has been a history in the past of putting iron in there to improve foam stability. The downside is iron promotes oxidation and actually if you're not careful, you'll end up with fairly brown foams. There was a history back in the day, some people in Canada using cobalt, that is definitely a no-no, because you don't want to kill the customer. But zinc, zinc actually works quite well, if you're legally allowed to do it, let me tell you that two milligrams per liter or two parts per million zinc, does improve foam stability. Now this interaction between the bitter acids and proteins occurs in the bubble wall. It doesn't happen in the liquid bit, it happens when they are concentrated in the foam. It takes a little bit of a time. When your next sitting down having a beer, you pour it out nicely, it got this nice foam, look at the foam, and it will start off being quite wet and quite liquid. But as the liquid drains away, the proteins and the bitter acids, aided by these divalent ions, they will link together and the foam will solidify. It will become more solid, firmer, and this is why when you then steadily drink the beer, you get the lacing patterns on the side of the glass. If you drain the glass before this foam has solidified, you don't get lacing. But if you wait awhile, you get these what I like to call beautiful cathedral windows of foam lacing the side of the glass. One of the most beautiful things that humankind has ever been exposed to. This is another good reason why you should always pour the beer out. The more bitterness, the more lacing. Maillard reaction products, melanoidin molecules on the pathway to melanoidins, they can stabilize the foam. The mechanism not very well understood. I don't think. I mentioned propylene glycol alginate. There is a risk because that can give you a clarity or insoluble, insolubility problem if you're not careful. Gums, polysaccharides. Some people have advocated using these. Some people believe that the beta-glucans in beer improve foam stability. Of themselves will not, to get enough viscosity from these beta-glucans to improve foam stability. The beer would be unfilterable. You'll have real problems. But we'll come back to that point later on. Then finally, the idea of putting extra protein in there. Indeed, we did a lot of work back in the day when I was with Bass in looking at albumin, egg white for this purpose. The reality is most beers will have sufficient protein in there and to put extra in there is not going to help too much. But some of the beers that are made with high levels of non-protein containing adjuncts, they may be improved by added proteins, but you have to be careful. Now, let me just go back to this business of gums. Let me tell you about a theory that came from a guy called Lawrence Bishop. Many years ago, Lawrence Bishop was the Research Director of the Watney the brewing company in the UK. He believed that when you kiln malt and roast malt, then you cook together proteins and polysaccharides or carbohydrates, things like beta-glucans, and they melt together. He believed this is very important for improve form stability. The theory goes that these hydrophobic polypeptides will of course, go into the bubbles and dry this carbohydrate with them. The carbohydrate, will dangle between the bubbles. Now, things like beta glucagon, of course, increase viscosity, so they'll slow down the rate at which liquid drains away. We talked about that in the physics of foaming. The beta-glucan can't concentrate in the foam unless it's attached to a protein. You need both. Bishop's theory as this is, what is happening to improve foam stability. You got the protein dragging this more viscous carbohydrate into the bubble wall. It has to be said that, there's not a lot of scientific exploration that has confirmed this one way or the other, but it's a nice story. It may be that the melanoidins and the propylene glycol alginate, they interact with the polypeptides and are dragged in and that's why they work maybe. Now let's turn to the foam negative materials. As I've said, the number one foam negative material is alcohol. The higher the alcohol level in the beer, the less stable the foam is going to be. Now a lot of people say to me, "Look, I go a barley wine, it's got a perfectly good foam stability." The answer is yes. Because you probably made it out of 100 percent malt. You've made it with some darker malts, possibly some little bit of chocolate or something. We'll come back to that later on. You've got a very high bitterness. You've got all these positives. The alcohol is competing with them. If you got a malt liquor, many of malt liquor, fairly low amount of protein coming from the malt, a lot of sugar, possibly. Very low bitterness. The alcohol is going to kill that foam pretty quickly. The answer is, it's a balance. Now of course, there's this war going on for who can come up with the most alcoholic beer. There's beers of over 60 percent alcohol. I couldn't afford to buy one an open one, but if I could, I'm pulling it out. I'm telling you there won't be any foam on that beer. Lipids. We've already talked about lipids being negative because they're hydrocarbons. Now earlier on I was talking to you about the detergents. Detergents can give you a stable foam. But what happens if you have a mixture of detergent and all lipids and proteins. The proteins can't interact with the bitter acids and stabilize the foam. The detergents can't interact with one another to stabilize the foam. They're getting in the way of one of, so these two different ways two different mechanisms to stabilizing foam, neither of them works, so it all falls apart. You got to get rid of the detergents and you got to make sure there's no lipid in the beer or on the vessel that you're pouring the beer into. We have addressed in some considerable detail the chemistry of the beer foam. In the next lesson, we'll talk about how you can quantify the form, how you can measure it, and start to make sense of what is happening in your brewing operations.
