That heady mix of pine needles, plum pudding and cooked turkey is more than the sum of its parts, reports Anthony King. It is Christmas.
Expectation is the first ingredient for a pleasant culinary experience. Hopefully, your prior experiences of Christmas will be happy memories and these will have set the stage for a good day. Odour memories are often short on verbal descriptors and are frequently formed when we are young, says Pam Dalton of the Monell Chemical Senses Center in Philadelphia, US: ‘Even a whiff of the odour can bring back those associated memories. Not just the memories from the Christmas you spent at your grandmother’s house, but also all those warm emotional feelings that went along with that.’
A festive feast for all the senses
Our expectations also prepare our brain. ‘Everyone has the experience of thinking they were going to drink one thing but then tasting something very different. Our brain and aroma receptors ready themselves and then we’re left in a state of confusion,’ says Dalton. In his Fat Duck restaurant in Bray in Berkshire, UK, Heston Blumenthal plays with these expectations by swapping flavours and colours in orange and beetroot jellies presented in combination.
Moreover, chemicals that generate aromas often occur in many contexts. For example, you might serve strong aged cheeses at the end of a long Christmas dinner and the whiff of those shot-chain fatty acids, such as butyric acid, will be welcomed. The exact same chemical in a vial marked ‘body odour’ will elicit nausea from your guests. ‘The label you put on something determines how you respond to it and what you think it is,’ says Dalton. As Blumenthal writes in The Fat Duck Cookbook, ‘It’s not the mouth but the brain that governs what foods and drinks we like or dislike.’ So festive table preparations, aromas from the kitchen, warm chatter among family, and the smell of pine needles mixed with Christmas pudding is the first course.
The next biggy is the bird. Roast turkey or goose are traditional and you don’t want to overcook the main event, but nor do you want to poison the family. Science has some sound advice here. Cooking begins when meat is heated above 38° C, but 55°C marks the spot where contractile proteins are denatured and water begins to be squeezed out, leaving the meat vulnerable to moisture loss. Once the meat reaches 65°C, further heating will make the meat cardboard dry and tough, and if you keep the throttle engaged and reach 75°C, you’re in for a lot of chewing. Don’t forget juiciness and tenderness depends on leaving some of the water behind. So buy a digital thermometer.
Second lesson: discard the 20 minutes/lb instructions. This is the advice of Peter Barham of the University of Bristol and the author of The Science of Cooking. ‘There is an enormous amount of physics, chemistry, and food science in understanding meat cookery, but essentially you are aiming to get the coldest part of the turkey up to a safe temperature.’ What matters here is the size of the turkey, not the weight. The weight increases as the cube of the size and the time it takes to cook increases by the square of the size. ‘If you cook at 20 or 15 minutes/lb, you will undercook a small one and overcook a big one.’ The problem at Christmas is that turkey sizes vary from the 3 kg ‘fledgling’ to the 17kg ‘moa’.
Another issue is the varied meat in the bird. Breast meat and leg meat are to the eye different because they are chemically different: they don’t both cook well at the one temperature. Harold McGee in his book On Food & Cooking is clear: the tender breast meat gets dry and tough if heated much above 68°C, whereas the leg meat is full of connective tissue and is chewy if cooked to less than 73°C. Either the leg meat is sufficiently cooked and the breast meat dry, or the breast meat succulent and the leg grisly. You can try turning the bird to expose the thigh joint to more heat or cover the breast with foil or strips of pork or baste it. The perfectionist carves the bird up. On Food & Cooking, according to Ubbink, is the book to have under your arm. Careful though – its weight fits its status as the textbook of science in cooking.
Of course, master chefs have not only taken the science onboard, but they’ve gone into the labs and researched the equipment. Chefs like Blumenthal now use sous-vide cooking, where they seal meat in bags to prevent flavour molecules escaping. The meat is then gently, but precisely, heated in a lab waterbath with a temperature set to plus or minus 0.05°C. It’s the kit biologists use to keep samples at the proper temperature.
Hervé This is one of the pioneers of molecular gastronomy and suggests turkey can be cooked at an oven temperature of ‘less than 100°C’ to retain juiciness. He has sought to assess the many steps, or precisions, which make up traditional recipes. An example of a precision that turns out to be wrong is that placing meat in a hot frying pan seals the juices; it adds flavour though. But the advice to leave meat to rest before eating is correct. This allows the heat to be evenly distributed over the meat so that it will still cook a bit further in the core, explains Ubbink. It also allows the water in the meat to redistribute itself, minimising loss of juices when the meat is cut before serving.
Job Ubbink, material scientist at the Nestle Research Centre in Switzerland, says science will help him get his sauce right this Christmas. With French-style sauces, you begin with boullion stock and boil it down. ‘Most people think you evaporate the water, concentrate the flavour,’ he says, ‘but you also provide heat for the reactions.’ These reactions leave a dark, brownish and very rich sauce, but drive out the volatile top notes. You can get a lighter, more balanced sauce with top notes and the base taste by freeze drying. ‘I just freeze it and sublimate the ice. Then heat the sauce briefly to induce some desired flavour compounds.’ In his experimental kitchen, Ubbink has access to freeze driers, high speed homogenisers, centrifuges and pacojets. But the chemistry of cooking doesn’t always require electricity. Writing in Accounts of Chemical Research (May 2009), This noted that grating carrots causes enzymatic reactions and compounds can be exchanged between a dressing and vegetable.
Paul Breslin, an expert in experimental psychology at the Monell Chemical Senses Center, notes that our taste senses are distributed in our mouths in a complicated fashion. It is not as simple as that salt, sweet and sour illustration from school textbooks. Dip your tongue into the crème of an espresso and you will be jolted by the bitterness, but do the same for Guinness and the bitterness is not there. You will have to throw the stoat to the back of your throat before it hits the right receptors and you taste its bitterness.
This variation in where taste receptors lie brings us to dessert. If you are baking cinnamon apple cake or spiced muffins, only sucrose will do. Breslin says artificial sweeteners mismatch the taste of sucrose because the timing of their sweet hit is not the same, but also because of their spatial profile. ‘Some of the high profile sweeteners have a tendency to stimulate more toward the back of the mouth than sucrose,’ he notes.
And science delivers the material needed to make the creamiest ice cream. The ingredient is all around us but it needs to be chilled to minus 196°C. Physicists and chemists are comfortable with such liquid nitrogen, says Barham: ‘It’s something we use to cool things down every day of the week. It is just stuff lying around the lab.’ With some safety training, it can be taken into the kitchen and used to freeze an ice cream mix in seconds so that ice crystals have no time to grow, leaving an incredibly smooth texture. In his cookbook, Blumenthal offers a recipe for ‘Nitro-scrambled egg and bacon ice cream.’ Plain vanilla is an option your plum pudding will also accept.
Physicist Nicholas Kurti famously told a Royal Society of London meeting in 1969: ‘I think it is a sad reflection on our civilisation that while we can and do measure the temperature in the atmosphere of Venus, we do not know what goes on inside a soufflé.’ Now, you can leaf through McGee’s 800-plus page tome for all sorts of scientific insights to help with your cooking. And Blumenthal’s recent Fat Duck Cookbook’s third section is devoted wholly to science.
But you don’t have to buy vats of gellan, gum arabic or kombu or use vacuum filters, rotary evaporators or liquid nitrogen in your kitchen to take advantage of the science of cooking. There is an accessible assortment of interesting insights large and small that can help you cook and understand cooking better and enjoy it all the more. And in his recent book Catching fire, Richard Wrangham has argued that cooking made us human from an evolutionary standpoint. I cook, so I am human. To understand is surely the next step.
Smells, spices and Christmas soup for the soul
Scientists have progressed in leaps and bounds in understanding the phenomenon of smell over the last decade, says Pam Dalton. ‘Smell is really one of the last sensory systems to give up its secrets.’ At some point, the goal will be to look at the structure of a molecule and predict what it smells like, though that is still some way off, she says. Smell is complicated though; for example, strawberry contains over 400 different molecules that make up its aroma. Moreover, people experience flavours and fragrances in different ways depending on genetics.
Also repeated exposures to different foods actually help determine what we smell. The reason caramel or toffee smell sweet is due to the tastes usually present when we encounter those odours. They are not sweet in themselves. Unlike the preference for sweetness and dislike of bitterness, there is no evidence that odour preferences are hardwired into the brain of children and we learn to like certain smells through associations. So the perfume gift opened and smelled on Christmas day is off to the best possible start – a positive experience.
Dalton has found that people can dramatically enhance their ability to identify the flavour of almond when a tiny drop of sweet saccharin is placed on their tongue at the same time, though this is true of Americans and Europeans but not Japanese people. So culture matters: ‘Within a culture you tend to find that certain odours are preferred and are thought to be calming and relaxing,’ says Dalton, ‘probably because many of those individuals have had similar experiences.’
And Christmas would also not be the same without all those warming winter spices like nutmeg and clove. But anything with spice, like black pepper, ginger, chili or mustard, has strong oral sensory components that are neither taste nor smell, says Paul Breslin. They cause irritation in the mouth and are really derived from the pain system.
You might serve soup at a tepid temperature. However, if you were to bite on a chilli, says Breslin, ‘the warm soup would then feel like it is burning and hot because of the way your thermal sensory system responds.’ He adds that there is a lot of similarity between physical heat and experiencing a chemical sensation of heat. And if your guest reaches for some fizzy water, the ‘fizz’ is from carbon dioxide bubbles bursting and causing a miniature pain response. For champagne, again it is the tiny carbon dioxide bubbles and pain, of sorts. Guinness drinkers do not experience such fizzy sensations because the bubbles are made of nitrogen.