Fats with more unsaturated triglycerides, such as vegetable oils, tend to be softer, while those with more saturated triglycerides tend to be firmer. Butter is mostly saturated triglycerides and is therefore solid at room temperature. Importantly, unsaturated fats are more prone to rancidity than saturated ones, hence butter is more resistant to rancidity than, say, soy or sunflower oil. (‘Trans-fats’ refer to the stereochemistry of unsaturated fats, but we won’t be going into that here.)
If the bonds between the fatty acid chains and the glycerol backbone break, this liberates ‘free‘ fatty acids, which are key to the development flavours ('good' and 'bad') in fats. But I’m getting ahead of myself, more on that in Part 2.
A Short History of Butter Making
The word butter comes from the Latin butyrum, which in turn comes from the Greek bouturon (where bous means ‘grazing ox’ and turos means ‘cheese’) . However, its manufacture, with sheep and goats’ milk rather than cows, can be traced back 4,000 years, meaning it predates olive oil.
Like many of the foods we eat, butter likely started off as a way to preserve nutrients—in this case, by extending the shelf life of milk in a rich, delicious, energy-dense way. Northern Europe, with its combination of pastures for livestock and cool climates, was perfect for butter, but in the hotter climes of southern Europe, butter spoils more quickly than cheese. Perhaps for this reason, the Greeks and Romans were a little snooty about the stuff and considered it to be food for northern barbarians. Greek comic poet Anaxandrides referred to Thracians as boutyrophagoi or “butter-eaters” (admittedly, other scholars said far meaner things about them), while Pliny the Elder, in his Natural History, calls butter “the most delicate of food among barbarous nations”, and then proceeds to describe its medicinal properties. Interestingly, Galen described butter purely as a medicinal agent rather than as a food—a notoriously tricky distinction best left for another time, but suffice it here to say the awareness that butter is good for you is millennia-old.
Introduction to rancidity and oxidation:
One of the central questions of the project was: what do we mean by ‘rancid’? As I explored this, I realised that there are in essence two relevant meanings—a more scientific one and a more cultural one. The two are not well correlated, and there lacks, among the general populace, including myself and most of us at the lab, a coherent lexicon to describe the latter.
Something rancid is typically defined as smelling or tasting unpleasant as a result of being old and stale, which is of course incredibly subjective: when we describe something as rancid what we often mean is “this tastes too old/weird for me” or “I am not willing to eat this”.
Context is a critical factor in determining what we think is palatable. I’ve discussed some examples of rancid butters above but, more widely, encouraging rancidity is actually not such a crazy idea: Cognac and Armagnac are both aged to develop ‘rancio’ character, which derives from oxidative processes ; in the UK, butter for toffee was often stored to develop some rancidity, to produce a more desirable stronger dairy flavour; and in the USA, chocolate manufacturers encourage their milk fat to undergo some rancidification by fat-digesting enzymes to develop modest cheesy and animal notes which enhance the complexity of the chocolate’s flavour . In analogous processes, the enjoyment of many nuts is augmented by roasting-induced lipid oxidation, which cause the development of new flavours , and highly prized Sherry, Marsala, Vin Jaune, Maury, Banyul and Madeira wines rely on flavour development via oxidative processes . In particular, because Madeira wines are so oxidised there is little scope for further oxidation and they are very stable, meaning that they can be stored for many years before being enjoyed.
In all these cases, particular audiences of people enjoy the results of ‘rancidity’—the flavours and value it adds to a product—without thinking of it as such. Furthermore, despite the words ‘rancid’ and ‘oxidised’ being more typically used in general parlance to imply negative hedonic qualities, there are also cases (eg. ‘rancio’ and ‘oxidised’ in the context of some wines and spirits) where the same words are used to describe positive attributes. Nonetheless, my experience of explaining to people the concept of this project showed me that phrases like ‘rancid butter’ and ‘oxidised fats’ do typically elicit a pained expression, and a sudden unwillingness to let me cook for them. So, if we want to develop a delicious, mildly oxidised, hedonically-positive butter—which has a flavour profile similar to cheeses that we know people love—then perhaps the first step should be simply to not describe it as ‘rancid’, or even the somewhat more technical-sounding but not entirely neutral ‘oxidised’ (more on the intricate chemical and linguistic relationships between ‘rancidity’ and ‘oxidation’ in Part 2). We could instead, for example, use the term ‘aged’ to draw parallels with the worlds of cheese and wine, where instances of similar physico-chemical processes elicit positive hedonic response.
Additionally, cultural priming is important, and people from different cultures have very different levels of sensitivity to rancidity. We have seen how Moroccans prize smen, yet for their French colonisers beurre rance was barbaric, offensive stuff. Roland Barthes, no less, writes on the subject:
"One day I was invited to eat a couscous with rancid butter; the rancid butter was customary; in certain regions it is an integral part of the couscous code. However, be it prejudice, or unfamiliarity, or digestive intolerance, I don’t like rancidity. What to do? Eat it, of course, so as not to offend my host, but gingerly, in order not to offend the conscience of my disgust…"
Barthes raises the notion of disgust which is key to understanding what rancidity is, and isn’t. As Rozin and Fallon note, "It is the subject's conception of the object, rather than the sensory properties of the object, that primarily determines the hedonic value." Thus, disgusting foods need not even have negative sensory properties: many people find the idea of eating some animal species (rats! dogs! horses! snakes!) revolting, and yet, from a nutritional and sensory perspective, they are pretty similar to those that they are perfectly happy to eat (piglets, sheep, cows, geese). Put another way, even stuff that tastes good can be perceived as disgusting. Rozin expands:
"The sense of disgust that overwhelms someone who bites into a wormy apple—the feeling of revulsion, the spewing of chewed apple pieces, the approach to the brink of vomiting—is not brought on because the worm tastes bad. The half worm is 'found' by seeing it writhing in the bitten apple; it is not tasted at all."
Elicitors of disgust vary enormously from culture to culture, and to a lesser extent from individual to individual within cultures (with some possible exceptions, such as vomit and faeces, which may be universal disgust objects—though surprisingly there is limited evidence to support this notion) .
Some conjecture on cheese and butter
Pondering the relationship between cheese and butter, I became deeply interested in why rancid butter and blue cheese, for example, are regarded so differently. Why is there widespread cultural acceptance for one but not the other? Here are some ideas—granted, they are speculative.