Now let me give you a little bit of basic chemistry and let me come back to this matter of water holding in on itself. Here are some water molecules and of course, I'm fond of telling people you don't need to memorize chemical formula, but it's useful if you know that the water is H_2O. Water consists of one oxygen atom, that's the bigger atom, and two hydrogens. They are, what you've got is so-called covalent linkages, the hydrogen and the oxygen. Each hydrogen shares a pair of electrons with the oxygen, I'm not going to go any more complicated than that. This is called a covalent bond. Now, the oxygen atom likes electrons more than does the hydrogen atom. Although it's sharing them, these negatively charged electrons, the oxygen drags them towards it. Because they're negative, that gives the oxygen a slight negative charge. But it gives a hydrogen because it's lost this proportion of negativity is more positive so you have this imbalance. The oxygen is slightly negative and the hydrogens are slightly positive. Now positive attracts negative so what this means is the slight positive on a hydrogen atom attracts the negative on another oxygen. You get these big linkages they're called hydrogen bonding between all the water molecules that are strongly interacting through this hydrogen bonding. This is one of the main forces wanted to drag the water in on itself to compress it. Now, I call this the Bamforth marital bed example. Let me illustrate what I'm talking about. Imagine that pair of electrons is actually a duvet and Mrs. Bamforth is oxygen and Dr. Bamforth is hydrogen. Mrs. Bamforth drags the duvet towards so she ends up with the duvet. I'm not sure there's any relevance to that, but it might help you to remember this concept of the unequal sharing of a pair of electrons. Why is something soluble in water and why is something not soluble in water? Let me give you this example in terms of sodium chloride. Sodium chloride is the stuff you sprinkle on your French fries, salt. Sodium chloride consists of a sodium, which has got a fully-fledged positive charge, so-called sodium ion, and chloride, which has got a fully-fledged negative charge, chloride. They are tracked by this positive-negative interaction. If you put them in water, they can split up. The sodium can be surrounded by water because all those negatively charged or slightly negatively charged oxygens are in the water, will surround it and interact with the positively charged sodium. All the positively charged hydrogens on the slightly positively charged hydrogen in the water can surround the chloride, the negatively charged, and so it dissolves. It divides up. If you've got something like this salt, sodium chloride, It's going to dissolve in water. Now compare and contrast that with something like an oil, a hydrocarbon. Think gasoline, think soap. Soap is not a good example, but think of fat. It doesn't dissolve in water. The reason is these hydrocarbons are exactly that. They consist of hydrogen and carbon, long chains of carbon with lots of hydrogens. The carbon and the hydrogen share the electrons equally. There's no slight positive charge on the hydrogen and there's no slight negative charge on the carbon. There's no charge whatsoever. You put that in water and it can't overcome the interactions between the water molecules. It can't overcome them. Not only that, there's no positive-negative interaction that can take place between the water and the hydrocarbon. The hydrocarbon just sticks in on itself, makes ultimately a lump. Try it yourself, go get some butter and put that into the water. It ain't going to dissolve. Anything that is a hydrocarbon or what we call hydrophobic water hating is not going to dissolve in water or indeed in beer. How do detergents give stable foams? Because detergents are blurgy hydrocarbons. The reason is a detergent, think washing up liquid, think bubble bath. I love to submerge myself in bubble bath. Please don't image that too closely. But nonetheless, detergents have got these hydrophobic chains, these hydrocarbon chain, but they've got a hydrophilic end. Something that likes water, usually got a charge on it. What happens is all of those hydrophobic groups, they all agglomerate in the middle, but the hydrophilic the water loving part is around the outside and making contact with the water. If you've got anything that's hydrophobic, it will insert itself and associate with the hydrocarbons in the middle and therefore dissolve. The whole complex will dissolve in the water because of the hydrophilic ends. This is why detergent will soak up a hydrocarbon. It will surround it, and the hydrophobic parts of the detergent will interact with it and then leaving around the outside the hydrophilic part, which is going to make it soluble in water. Proteins stabilize foams in another way. Instead of having all of these hydrophilic atoms surrounding the bubble, whereas proteins, what you have is the protein coating, the surface of the bubble, and interacting with the bitter acids, so you form this matrix. It all holds together because of the proteins and the bitter acids linking together and making a framework, a skeleton, around the bubble wall. Let me go on to explain why I've spent some time doing that. Let me talk about this fancy description, generalized, amphipathic polypeptide hypothesis. This is something that dates back, we did this in 1983. I'd say many of you are listening this today weren't even born in 1983. This is a piece of work that I did with a guy called Phillip Slack back in BRF, Brewing Research Foundation and not feel sorry back then. What we tried to do was to divide up the proteins from beer, and also from grain, using something called hydrophobic interaction chromatography. Now, let me walk you through it. Any biochemists knows there's a material called sepharose. Sepharose is a little bead, and you can attach things to it. What we attached to it was octyl. Octyl is a hydrocarbon, CH3CH2CH2CH2CH2CH2CH2CH2, eight carbon atoms. A hydro carbon chain, in other words, hydrophobic. Earlier on, I said that if you've got salt that rather dissolves in water, if you add salt solution to a beer, you will tend to exaggerate these hydrophobic interactions. What we did was to take our beer or a protein extract from the grain, and we added salt to it, and then float it through this column that was packed with Octyl Sepharose. Anything that goes straight through is relatively hydrophilic, water loving, because it will not stick onto these hydrophobic surfaces. Then you switch out the salt and replace it with just water, so start flowing the water through. Anything that's loosely bound, that will be washed off by water. This will be moderately hydrophobic. Then if you replace the water with glycol solution, now you start to wash off the very hydrophobic polypeptides. In this way, you can separate the proteins into hydrophilic, somewhat hydrophobic, very hydrophobic. We looked at the foam stability. We looked at it using a method called routing method, which I'll talk about in a later lesson. We measured the foam stability, the head retention value, at a range of protein concentrations for each of these fractions. You can see that you've got some foam stability with all of the fractions. If you look at any individual protein concentration, the more hydrophobic, the better the foam stability. This is not rocket science, and it falls into line with everything I've just told you. If something is hydrophobic, it doesn't want to linger around in the beer. It wants to leave the liquid, the water, and go into the bubble, and there stick together with other hydrophobic materials. Partying in the bubble wall. This is why hydrophobicity is so important. Another of my scientists, Akiko Onishi, a little while later, took these three protein fractions and she separated the proteins in another way. She isolated the hydrophobic, the moderately hydrophobic, and hydrophilic. Then she took each of those fractions and she divided the proteins on the basis of how big they were, the so-called molecular weight. This illustration you can see in front of you is a fairly stylized, simplified version of what she found. But the important point is this, exactly the same proteins were present in all three fractions. In all of them, you've got lipid transport protein, and proteins here, and other proteins as well. How can this be? You can divide proteins up on the basis of the hydrophobicity, but he got exactly the same proteins in each fraction. The answer is, it's all to do with the shape. A protein has got a three-dimensional shape. It calls in itself. Imagine if you like a ball of wool, or a chain that's being put in a pile. When it comes to proteins, all of the hydrophilic, the water loving parts are all focused on the outside, and on the inside of the protein hidden away in the middle are all the hydrophobic groups, not all of them but many of them. But if you denature the protein and you unfold it, now, you're going to change the shape and you're going to release or expose the hydrophobic interior. This why lipid transport protein improves its foam stability after boiling. Imagine if you were, I'm lipid transport protein, just doing this, minding my own business in word. Along comes you, the brewer, the ruthless brewer, and you boil it, and so I'm going like this now. I'm unfolding and the hydrophobic interior has been exposed, I am becoming more hydrophobic, more foam stabilizing. The important point is that it's the hydrophobicity that is really a very important thing. That's why if a protein has got hydrophobicity, it will tend to be a superior foaming agent. This is why lipid transport protein gets better after boiling. That's why I personally believe that this hydrophobic nature of protein is the thing you should think about first.
