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Emulsions Thursday, Nov 1 2012 

It is impossible to mix oil and water.  On the face of it, it almost seems peculiar that anyone should want to take an interest beyond that.  There are any number of occasions when mixing oil and water is clearly unnecessary (in the fuel tank of a car), or even dangerous (chip pan fires should never be put out with water).  However, a few minutes’ worth of Googling suggests that there are at least as many reasons why it is useful to mix oil and water.  Mayonnaise, paint, milk and even the humble pork pie would all be quite impossible without the principle of being able to combine water and oil; without emulsions.

A droplet of fat (orange) surrounded by emulsifying amphiphiles. Photo copyright: flatworldknowledge.com.

The hidden ingredient in mayonnaise is the vinegar; most people know that it contains oil and egg, and sometimes even mustard powder, but watery vinegar is guessed less often.  The inclusion of both oil and vinegar is the main underlying physicochemical problem with this food: to make it, you need to mix oil and water into a homogenous fluid.  This requires a third agent: an emulsifier.  In this case the egg yolk and mustard powder are the emulsifiers.  All that is required is that the oil, vinegar, egg and mustard are mixed together in the correct proportions, and a mayonnaise is formed.  The egg’s yolk contains a variety of lipids that are capable of encapsulating globules of fat that can then be suspended in the mixture of water and vinegar.

Emulsions used in paint are a bit more complicated, requiring several ingredients to work properly.  They are also quite different to other types of paint, such as oil-based or acrylics).  Emulsion paint relies upon particles that are dissolved in a medium containing water and another, minor, solvent.  It is these solvents that evaporate when the paint dries, during which the particles polymerise to form the skin we know of as dry paint.  The emulsion has been used as a sort of vehicle, to deliver the material we wish to use to create an opaque, coloured film on a surface.  However, the emulsion is not completely lost, as not all of the water leaves the mixture.  The layer is still capable of taking on further water in more humid conditions (e.g., in a bathroom), meaning the film cast on the surface is susceptible to water damage.  Paints that are suitable for more humid environments include masonry and enamel paints, that are based on oily systems that are designed to provide a waterproof seal for a given surface.

Pork Pies and Milk in front of a painted wall. How many emulsions are there?

Milk is a relatively simple and dilute emulsion, containing a mixture of fat, protein and water.  In this case, trace amounts of lipids, and milk proteins, are used to encapsulate the triglycerides (fat) that can then be suspended in the water.  It is therefore similar to mayonnaise in that amphiphilic species are used to create droplets that are then suspended in water.  However, milk uses amphiphilic proteins as well as lipids, whereas mayonnaise does not rely upon such proteins.

That just leaves us with the delicate matter of the pork pie.  This is really a fudge in terms of the basic principle of an emulsion, or rather, two fudges.  Firstly, the meaty part in the middle relies upon an emulsion so that the pork fat in it does not form unattractive blobs.  Secondly, the pastry relies upon a sort of emulsion in order to form an homogenous mixture.  The pastry requires the use of fat, partly because it was a useful source of energy in days gone by, but also so the pastry was edible.  The pastry made without fat in the middle ages was rather like stiff cardboard.  This was fine for keeping bugs and rodents off the meat, but was expensive and wasteful of flour.  This led to the accidental use of an emulsion for creating the pastry that holds it all together.  This is not uncommon in baking, batters and pastes are emulsions, nice and runny. Doughs are emulsions as well, but with fibrous protein in them.  If you fancy making an emulsion yourself, you might like to try one of James’ recipes from the final of the Great British Bake Off, for a Chiffon cake of a Union Jack (pp21).

Another Great British Bake off. Seriously?! Sunday, Oct 21 2012 

There are, as you will have seen if you watched the tantalising final, plans for a fourth series of the Great British Bake off.  Auditions may even be under way already.  My initial reaction to this news was a petit mort.  A ‘little death’, just like the one the French refer to when they use this phrase, for the moment that some poor souls apparently suffer, of sang froid after sex.

I may be over-stating it to say that the final of the GBBO was orgasmically thrilling, as it clearly was not.  The Great British Bake off is struck deeply by the terrible flaw that the viewers cannot either taste or smell the baked goods being produced.  This is perhaps why the former is commented on blandly or briefly and the latter not at all.  This is in contrast to the appearance that gets a good deal of comment.  Inevitably, however, the food must be judged partly or even mainly on flavour.

It is perhaps vaguely peculiar therefore that the show works at all.  Of course it has beautifully able and contrasting judges, the tough-guy Paul Hollywood and the gentle but powerful Mary Berry.  The presenters number Sue Perkins, who provides witty wordplay and thinly-scripted narration clearly written by someone else, and Mel Giedroyc who does, well, something.  Not sure what.  Knows the names of tedious types of polish bun?  Talks in an unnecessarily dramatic tone about trivial occurrences?  I am not sure.

What it also has is someone a bit canny who does the auditions.  They know they have twelve contestants and they seem to think, probably rightly, that it will not work that will if the standard is too high or too low.  So they choose about six people who are a bit crap and will clearly be the first half to go (you can virtually write the list in week one) and about six who are competent but may or may not have the stamina to last it out.  Certainly they have some assessment system whereby they can ascertain whether potential bakers know their stuff or not.  There are clearly a number of people who are proficient in things I have never heard of and they cannot fail to check this before the whole thing kicks off.

Someone relatively senior of the production team, probably the director and the producer in fact, select rushes that edit together into something that manages to be both informative and watchably entertaining.  There are not endless tears and embarrassments, nor are there the sorts of humiliating and undignified scenes that appear in every other piece of reality television I have ever seen.  I call it reality television because the GBBO consists of amateurs doing a difficult thing, rather than a competition between seasoned professionals.  So much of the point of putting ‘ordinary’ people on television in a setting that some arse has called ‘reality’ is the schadenfreude for the viewer of watching someone who is at best ill-qualified and at worst as stupid than they are, fail or almost fail at something.  Those programmes are then designed to carry the supposed tension of the obvious outcome from the outset until some moment near the end, with an ‘emotional rollercoaster’ along the way.

Despite its faults, the GBBO manages to avoid any of this dross.  In that respect I find it a breath of fresh air.  It has made the celebrating of achievement by people who are able but not formally trained on television acceptable.  It means I can watch something that is not comedy, drama, documentary or crap, on live television, and for that I am grateful.  But where will it go next?  The flavour-flaw in the format can never be done away with and unless at least one of the judges or presenters dies, preferably during filming, the GBBO piping bag will flow steady for a while yet.  I am vaguely tempted to watch the next series, as long as it is not on too soon.  It is almost a compulsive urge: partly because it seems to be good television, and partly because I do like baking.  And eating.  Perhaps those things are the allure for me.  This sets up an uncomfortable paradox: the one place where those things can be satisfied is if I actually become a contestant on the programme itself.

I suppose that means I have a crème patissière to practice.  Just as soon as I find out what that is.

How Hot is Hot? A Burning Question About a Hot Condiment Thursday, Jan 19 2012 

Plenty of people like a good hot curry. I am not one of them, but I think that most people have met, or know, someone who likes wolfing down the hottest curry in the house as a matter of pride. I do know someone who likes to munch on the same kind of hot curry but exquisitely slowly. Either way, it is safe to assume that pretty much anyone who has had a strong curry, and either enjoyed it or not, will remember the flavour forever.

There has even been a certain amount of study on this topic: some time ago, the compound capsaicin (Figure 1) was identified as the cause of the hotness. Several related compounds have also been identified, some of which are ‘hotter’ than others. This led to the desire to measure the ‘hotness’, resulting in the Scoville Heat Unit, and the Scoville Scale.

There is also the well-known opportunity for a schadenfreude with curry flavours. As it can be a strong flavour, when someone bites on something unexpectedly teeming with chopped jalepeños, the shock on their face is palpable. However, this shock can also be turned on its head with respect to public order. Recent anti-capitalist protests in America have given rise to some disturbing images of people sprayed with a capsaicin formulation (commonly known as pepper spray) either intentionally, or apparently not.

While these are shocking, and the mental and physical distress caused by the use of this ‘riot-control agent’ are readily understood, other factors are also important. The use of pepper spray as a weapon of self-defence, against a rapist or criminally violent attacker for example, seems not unreasonable. However, the link between pepper spray and deaths in people exposed to it who also have compromised respiratory function, increases the interest in managing the use of pepper spray, both politically and scientifically.

Figure 1. The structure of capsaicin, showing a more polar section (left) and a more lipophilic one (right), giving rise to a comparison with lipid structures.

One way of taking things further is to understand the science behind what is happening when pepper spray is used. A judgement can then be made about safety and appropriate conditions for use. The structure of capsaicin (Figure 1) suggests that it has a lot in common with what we know about lipid structure – a relatively polar (hydrophilic) section as one end, and a lipophilic hydrocarbon chain as the other. However, it is not just the lipid-like properties of capsaicin and its related compounds that give rise to the effect we remember so readily – after all, we eat lipids of one sort or another in almost every mouthful and most do not have the same effect as a vindaloo on our taste buds. This hot sensation is due to an effect of the capsaicin on nerves that feel heat (thermoception) and pain (nociception).  Recent work has suggested that there is a direct impact on the activity of calcium channels in nerves and earlier work has found that such exposure was responsible for permanent damage to the cells involved.This is quite sobering when looked at from a riot-control angle. If a chemical is able to cause innervation, as measured by pain, it is arguable that it is a drug. If it is a drug, strict licensing laws would apply. This also influences the dose(s) that can be used legally. Perhaps we need to reflect on the use of pepper spray of indiscriminate dose, as a crowd control agent?

E Numbers: Emulsifiers Sunday, Oct 16 2011 

Figure 1. Mayonnaise, something that necessarily requires the emulsification of fat and water.

Emulsification is the word scientists give to mixing liquids together. Specifically, it is the process by which immiscible liquids, liquids that cannot normally mix, are mixed together. The chemical agent used is called an emulsifier. Emulsifiers are not unique to food, we use emulsifiers to clean ourselves (soap), and in order to produce medical injections.

Emulsifiers in Food

The most familiar emulsifier is probably the egg. Eggs are used as an emulsifier in everything from cakes and custard, to mayonnaise (Figure 1) and from hollandaise, to soufflés. What the egg is doing chemically is allowing the other ingredients to form a stable emulsion (mix). Interestingly, egg itself actually contains two types of emulsifier: one is protein, the other is lecithin (Figure 2). They both have chemical properties that are shared by both water and fatty substances. This helps mix things up sufficiently well to make a homogeneous mixture of water, fat and lecithin, that looks not unlike baby sick. There are others that are used regularly in cooking too. As well as the egg in mayonnaise, mustard powder is also added to many recipes. This also helps it to stay homogeneous.

Figure 2. The structure of lecithin. The blue section is water-liking.


Industrial Emulsification

In industrial food production, several harmless emulsifiers, not common-place in the home, have been used for some time. One such is xanthan gum. The name is perhaps misleading as it is not a gum as such when bought, but an off-white powder that is usually accused of being either cocaine or flour. The usage of the word gum is perhaps clearer when we consider the properties it has on being mixed with fat and water. Figure 3 shows the transformation. Here, I include weights and volumes so you can do this yourself if you want to.

Figure 3 – mixture of oil, water and xanthan gum (E415) forming an emulsion that is also thickened. A: oil and water, B: xanthan gum as available commercially, C: xanthan gum with oil and water before shaking, D: water, oil and xanthan gum mix after shaking, showing solidification, E: solid mixture as compared to xanthan gum.

In part A we see the oil (clear yellow layer, 10 mL) above the water (colourless layer, 25 mL).  Adding the xanthan gum (B, 5 g) appears to do little initially (C), however a brief agitation of the system leads to homogenesis of the three substances (D).   Not only do we have an homogenous mixture, but also one that is thicker than it was previously – squeezing it out gives the appearance of an off-white turd (E).  Said turd goes brilliantly with a sprig of basil or rosemary and glass of chilled white Sancerre.