It is curious that we talk so little about the flavour of formula, given that it is the main food many babies taste for that crucial first year. Because any given brand of formula milk does not vary, it seems to have an even greater ‘imprinting’ power than breast milk. Babies who cannot tolerate regular cow’s milk formula are sometimes given special ‘hydrolysate’ formula, whose proteins have been broken down (hydrolysed) to make them more digestible. To adult tastes, these formulas taste especially nasty, with a sour cheesy tang and a strange hay-like odour. Mennella and Beauchamp followed children who had been fed with two different hydrolysate formulas.19 Objectively, both of these milks tasted equally unpleasant. But to the infants, the particular formula they had been assigned – sour or not – taught them how food should taste. When the two brands were switched round, the infants drank less: they preferred their own bad-tasting formula to the other one. More strikingly still, children aged four to five who had been fed on these sour-tasting hydrolysates as babies showed more positive feelings about sour tastes and smells than children who had been fed on breast milk or regular formula. This is vivid proof that anything can start to taste good if you have enough positive memories of being fed it by a parent. The obvious implication is that formula-fed babies would benefit from having their milk flavoured with vegetables.
Formula can never match the myriad benefits of breast milk, which range from lessening the risk of eczema and ear infections to reducing the likelihood of type 2 diabetes later in life to promoting healthy gut microbiota. But in the developed world, as we’ve seen, most mothers are unable or unwilling to breastfeed exclusively for the first six months. With each of my own babies, I gave it up for one reason or another (illness, work, bereavement and a child with feeding difficulties) at three months. Until they were a year old, when they were old enough for regular whole cow’s milk, I’d have been glad to buy formula that was mildly scented with a range of green vegetables, just enough to give them a memory of spinach when the time came for them to try veg for real.
Instead, in many countries, formula milk has been flavoured, if at all, with vanillin, the artificial vanilla flavour that goes into industrially produced sweet foods, from ice cream to biscuits to cake. Vanilla milk has a long history. Back in 1940, the head nurse of the children’s hospital in Philadelphia recommended tempting reluctant feeders with three drops of vanilla essence in each bottle.20 Internet forums suggest that there are still many desperate parents who resort to vanilla extract when a baby rejects the bottle.21
Since 1981, international food standards (the Codex Alimentarius of the World Health Organization) have stated that no flavourings should be added to infant formulas aimed at newborns. But vanillin is still a key ingredient in many of the ‘toddler milks’ marketed at children aged one and over. In China, vanillin is prohibited in infant formula but it continues to be illegally added by many manufacturers. In 2014, a team of chemical analysts found vanillin in four out of twenty samples of infant formula randomly purchased from supermarkets in the city of Wenzhou.22
Of all the flavours you could think of with which to ‘imprint’ a child, this is possibly the least useful from a health standpoint (except, perhaps, for chocolate: in 2010 the American company Mead Johnson withdrew its ‘premium’ chocolate-flavoured Enfagrow toddler milk amid complaints from leading nutritional scientist Marion Nestle that it was training kids to ‘like candy’).23 The effects of vanilla milk are lasting. In 1999 some researchers in Germany tested the effects of the vanilla that had been in German ‘bottle milk’ for some years.24 They asked 133 people to try two different ketchups, one of which was straight-up tomato ketchup and the other, bizarrely, had been flavoured with vanillin. (The reason the researchers chose ketchup was precisely because it is not normally associated with vanilla.) Of the respondents, the majority of those who had been breastfed had a preference for the pure ketchup, while the majority of those who had been reared on vanilla formula preferred the strange vanilla ketchup. Their baby milk had brainwashed these unfortunate people into thinking that vanilla made everything taste better.
Clearly, spinach milk would be a better plan, assuming it could be made safe for tiny infants. It will probably never take off, though. Over time, the odds are that babies would accept it and even prefer it, just as the hydrolysate babies with their bad-tasting formula think that milk is meant to taste sourish and cheesy. It’s the parents who would find vegetable milk hard to accept. We want our babies to have milk that corresponds to our own memories of childhood. Manufacturers know that you can only sell baby food by making it appealing to adults, which is why baby rusks are sometimes sweeter than doughnuts and why for decades, until it was banned, jars of baby mush came seasoned with MSG, to give it more savoury taste. When vanilla is found in baby foods, it has been put there to attract not the children themselves – who, as we’ve seen, can become emotionally bonded to flavours that are strange, sour or strong given the right memories – but to please adults. The babies are not the ones who buy the food. It is the grown-ups’ memories that the food companies are trying to appeal to.25 As they warm the sterilized bottle, parents sniff their baby’s milk; or maybe take a tiny sip. It is they, not the babies, who have memories of how childhood milk ought to taste: creamy and sweet, like milk left behind in the cereal bowl.
Do you remember your first passion fruit, your first avocado, your first Thai green curry? Such flavour memories can seem inconsequential, the stuff of gastronomes. ‘Ah yes, it was in Marseille in 1987 that I first tasted an authentic bouillabaisse.’
Yet, from the perspective of neuroscience, food memories are not something slight. Registering different flavours is one of the main ways that our bodies interact with the world around us. Amazingly enough, the human olfactory bulb is the only part of the central nervous system that is directly exposed to our environment, through the nasal cavity. Our other senses – sight, sound and touch – need to travel on a complicated journey via nerves along the spinal cord up to the brain. Smell and flavour, by contrast, surge direct from plate to nose to brain.
Conventional wisdom used to be that humans have rather a weak sense of smell, compared to that of other animals: dogs, say (witness the fact that we don’t have sniffer humans at airports). But recent research suggests the contrary. We may not have a bloodhound’s ability to track a scent, but our olfactory discernment is second to none. We can detect a drop of Worcester sauce in a glass of tomato juice; or the scent of fear in another person’s sweat.26
When I say that we discern smells and flavours, what I should really say is that we create them. Flavour is not actually in food, any more than redness is in a rose or yellow is in the sun. It is a fabrication of our brains and for each taste we create a mental ‘flavour image’, in the same way that we develop a memory bank of the faces of people we know. The difference is that whereas faces fade when you haven’t seen them in a while, flavours and smells have a way of lodging themselves indelibly. What you taste as a child is still there in your adult brain, even if you haven’t thought of it for years. The Norwegian Trygg Engen, the ‘founding father’ of the study of smell and memory, characterized our sense of smell as ‘a system designed not to forget’.27
In 1991 the biologists Richard Axel and Linda Buck discovered that olfactory receptors – cells in the nose that detect odour molecules – make up the largest single family in the human genome. Out of around 19,000 genes, Axel and Buck found, nearly a thousand – 5 per cent – are olfactory receptors. Their research finally unlocked some of the mystery of how humans can remember and discriminate between so many flavours and smells (and, thirteen years later, won them a Nobel Prize).
What makes the human system of olfaction so sophisticated is not just the receptors themselves, but the way they interact with our large brains. Each receptor cell is fairly specialized: it can detect only a small number of substances. But when you smell or taste something – a loaf of freshly baked bread, say, or lemon zest sprinkled over a stew – the receptors send messages to the olfactory bulb in the brain. Here, each flavour becomes encoded in its own particular pattern in a part of the olfactory bulb called glomeruli. A glomerulus has been described as a ‘detection point par excellence’. Each