On the label it simply said “Value Vegetable Lasagne”. But from the picture on the box, I could see that the manufacturer was being modest. This was going to be a carnival of flavour, with a delectably rich sauce, layers of silky pasta, a light-yet-creamy bechamel topping and the savoury tang of crispy melted cheese.
I dutifully removed the cardboard sleeve, stabbed the film lid and set it in the microwave. Two minutes later, however, the dish that slopped onto my plate was unrecognisable. The cheese had liquefied into an oily slick, the bechamel had congealed and the pasta was as rubbery as overcooked calamari.
We’ve all had one: the barely edible microwaveable ready meal. They might be ready in minutes, but crafting a recipe that works is an onerous process – one that requires a surprising amount of science. At the high end of the scale, this includes elegant techniques pioneered in Michelin-starred restaurants; at the other, plenty of E numbers.
To understand why, it helps to get to grips with the queen of chemical reactions, the Maillard reaction. First discovered by the French chemist, Louis-Camille Maillard, back in 1912, it’s the most widely practiced chemical reaction on the planet. It happens in millions of kitchens every day, though very few people have heard of it.
Essentially, something delicious happens when you mix amino acids with certain kinds of sugars, then heat them up. New compounds begin to form, which turn the food brown and contribute to its flavour.
These Maillard by-products are responsible for the earthy sweetness of coffee and the malty, caramel notes in beer, as well as the appetising aroma of baked bread, chips, fried onions, barbecued meat, biscuits, toasted marshmallows, and most other foods that we find irresistible. It’s one reason spices are fried or toasted before they’re used, and why there’s no comparison between roasted and boiled potatoes. Our attraction to them might be innately human, since they’re a by-product of cooking and we’re the only species that can do this (though with some prompting, chimpanzees are getting close, scientists reported in 2015).
“It’s a very complicated reaction,” says Steve Elmore, a flavour chemist at the University of Reading. Depending on the proteins and sugars involved, there are thousands of possible by-products. Amino acids with higher levels of nitrogen tend to lead to more nutty smells, while the more potent varieties, according to Elmore, tend to involve sulphur and smell of onions.
The problem is, the reaction can’t happen if the food is too wet. “If you’ve got a raw potato in the oven, it’s got around 80% moisture,” says Elmore. Once it gets to boiling point, water starts to evaporate and its surface begins to dry. “You need to get the water content down to about 5% before the Maillard reaction will take place and you get all the nice cooked flavours and brown colour.” This is why roast potatoes are usually brown on the outside and white on the inside.
Less scrupulous manufacturers attempt to mask the lack of delicious browning by loading their products with salt, sugar and monosodium glutamate (MSG)
Microwaves work differently. Rather than heating the surrounding air, they bombard food with tiny, high-powered radio waves that heat up the molecules inside as they pass through. This relatively even cooking means the surface never gets hot or dry enough for the Maillard reaction to occur, leading to disappointingly pallid toppings on shepherd’s pies and lasagnes.
This also means that ready meals tend to taste a bit bland. One early study found that beef cooked in the microwave had just a third of the scrumptious aromatic chemicals of meat that was cooked conventionally, while another found that microwave-baked bread was, frankly, disgusting.
Less scrupulous manufacturers attempt to mask the lack of delicious browning by loading their products with salt, sugar and monosodium glutamate (MSG), which gives food a savoury taste and is reputedly abundant in Chinese takeaways. Back in 2015, a joint investigation by The Telegraph newspaper and campaign group Action on Sugar found that some British supermarket meals contained twice as much sugar as a can of Coca-Cola, or around 13 teaspoons (that’s four teaspoons more than the recommended daily amount for an adult male).
But it doesn’t have to be this way. As the demand for meals with a fresh, homemade flavour grows, manufacturers are beginning to take a more sophisticated approach. And this starts with choosing the right ingredients. “The reality is, not everything is suitable for cooking in a microwave,” says Benn Hodges, the head chef at Eat First, a company specialising in gourmet ready meals. He’s worked at some of the best restaurants in the world, including the Michelin-starred branch of Roka in London.
Take salmon. The striations on individual fillets are where the separate muscles used for swimming join up. They’re stuck together with collagen, which melts and turns to gelatine as it cooks – this is why fish turns flaky. At the same time, proteins in the muscle begin to denature and coagulate – this is why it turns opaque.
As all good cooks will know, the main dangers with salmon are that it will fall apart, and that shrinking muscle fibres will squeeze out moisture, turning your previously juicy dinner into a dry mess. The best way to avoid both is to get it as hot as possible and cook it fast, and this is where microwaves come in.
Coming from my background I never would have dreamed of cooking fish in the microwave – Benn Hodges, chef
Most microwaves use a wave frequency of 2.45 gigahertz, which is most easily absorbed by water, fat and sugar. The more of these molecules a food contains, the more quickly it will cook, which is why high-fat, high-water fish steaks are ideal. As a bonus, water doesn’t boil in the microwave until it reaches 105 C, so whatever you cook will retain more moisture. And finally, they preserve more of the healthy pigments that give salmon its orange-pink colour and fragrant aroma.
“Coming from my background I never would have dreamed of cooking fish in the microwave, but it really works,” says Hodges.
One dish Hodges was particularly keen to recreate in ready meal form was Roka’s salmon teriyaki, which is cooked over charcoal on a traditional Japanese barbecue called a robata. To make sure the fillets are steeped in Maillard compounds, just like the real deal, first they’re seared in a 300C (572F) degree oven. “The salmon is already coated with the sauce and the oven just creates a beautiful glaze, as if you were doing it on a robata in a restaurant,” he says.
To avoid overcooking it – after all, the fish still has to be microwaved – the golden fish is removed after just a minute and cooled right down. “It’s really about stopping the cooking process quickly,” says Hodges. “We have one of the best large chillers you can buy, and this will take something from, say, 100 degrees to under zero in less than five minutes.”
These are extremely popular in the industry – in fact, they’re often the only way to comply with food safety regulations – because they have the added benefit of preventing harmful bacteria from growing in the comfortable, lukewarm conditions while the food is cooling down.
Which brings us to the next problem. Most microwaveable dinners come partially-cooked, which means they must run the gauntlet of all the same perils that ruin leftovers. The biggest culprit is the dreaded “warmed-over flavour”, a rancid taste that tends to develop in meat that’s been cooked and then refrigerated. It’s often said to taste like a cross between cardboard and damp dog hair, and occurs as a result of oxygen reacting with fats in the meat.
In this case, most manufacturers overcome the problem by adding antioxidants, which prevent oxygen from reacting with fat by sacrificing themselves. These can include synthetic E numbers such as butylated hydroxytoluene (E321), but also herbs – rosemary is particularly effective – spices, vitamins, and even lemon juice. Ironically, the Maillard compounds that are often absent in ready meals are also potent antioxidants.
The cold air in microwaves means that steam tends to quickly condense back into liquid water
Other manufacturers just make sure their food is eaten before this happens. “There’s food in the marketplace that has a shelf life of up to two months and actually I think it’s kind of scary. In one instance we found a company that was making refrigerated children’s food that was supposed to be healthy and it had a shelf life of three months,” says Hodges.
There’s also the issue of soggy food. The cold air in microwaves means that steam tends to quickly condense back into liquid water. This stops food from developing a crispy surface and even actively adds moisture into foods that already have one – preventing crusts from forming on bread and turning pizza soggy.
But here too, science can help. Enter “susceptor packaging”, a clever new technology that can crisp bread in the microwave. It usually consists of a cardboard tray lined with plastic, which in turn is coated in a fine film of metal. Popular wisdom has it that metal gets so hot in the microwave that it will definitely burn your house down with a massive, apocalyptic explosion. But this isn’t strictly true.
It actually depends on its shape; flat sheets tend to just get very hot, while anything angular, such as a piece of foil shaped to cover a dish, will eventually ignite. It’s down to the way electric charges accumulate more on angular surfaces, and it means that susceptor packaging gets just hot enough for a crust to form, but not so much that you’ll be scraping embers out of the microwave for the next few months. They’re also just hot enough for the Maillard reaction to turn your dinner a more appetising shade.
But perhaps the most offensive failure of microwaves is that bland ready meal taste. This is, of course, partly to do with the lack of browning, but it’s also down to the fact that microwaves hold cold air. Conventional ovens dry the surface of food, which prevents aromatic compounds from being able to escape as they evaporate. The hard crust of say, a lasagne cooked this way, forms an impenetrable barrier. Meanwhile the soft, gelatinous mess of bechamel and cheese fresh from the microwave is no match for fleeing flavours.
Hodges overcomes this flaw by incorporating pickled vegetables into his meals. “This helps with adding a real touch of fresh flavour and acidity, giving the dish a less homogenous palate,” he says.
Ever since being invented by accident in 1945 when an engineer inadvertently melted his snack, microwaves have been revolutionising how we eat. Supermarket lasagnes may never have that crispy, oven-scorched topping that we crave, but science is making them more delicious every day. Failing that, you could always, ahem, heat your ready meal in the oven.