Does refrigeration kill nutrition?
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Krish Ashok wrote today’s newsletter. He is the author of the book Masala Lab where he breaks down the science of Indian cooking. He is not a chef but cooks daily. You can follow him on Instagram and Twitter to understand food better.
I was in Ladakh in the last week of December. Yes, I am that guy who picks the middle of winter to visit one of the coldest inhabited places on the planet because I am not a fan of tourists.
The place was otherworldly and surreal. There is something about the visceral monochrome beauty of the place where altitude and temperature conspire to prevent plants from growing for most of the year. Ladakh is all shades of grey and snow white in the mountains, and shades of brown flanking the turquoise blue of the Indus and its tributaries.
As an agricultural species for the last 8000 years or so, it’s generally hard to imagine humans living in a place that so conspicuously lacks the colour green, but Ladakhis seemed to have figured it out. I met locals who worked with Ladakhi women entrepreneurs who use the short, three-month summer and the incredible fertility of the Indus river valley to grow some of India’s finest organic produce.
You see, in Ladakh, the idea is to grow as much as you can during those three months and then expose it to the bone-dry, zero-humidity, microbe-unfriendly climate — and then dehydrate it all. Every fruit, vegetable, and herb is dehydrated, its flavours enhanced by the harsh growing conditions, further concentrated in the absence of water and then stored in jars for the rest of the year.
In winter, Ladakhi grandmothers just reach for those jars, pick up sun-dried produce and meat and add it to boiling water to make the kind of umami-laden soupy broths that we have come to love.
While the curious romantic in me marveled at human ingenuity in the face of extreme conditions, the engineer in me had another realisation: Ladakh is quite literally an open-air refrigerator for roughly three-quarters of the year.
The very existence of Ladakh should convince people in the rest of India that a refrigerator is a life-saving preserver of food and not a diabolical appliance that encourages the consumption of stale food. Low temperatures slow down time and time is the enemy of freshness. The smart use of refrigeration and freezing will actually allow you to eat healthier meals more often than not.
Roughly 3000 km south of Ladakh, my maternal grandmother spent about 70% of her adult life in the steamy kitchen of her tiny house in the oppressive 90% humidity of Chennai. The running joke in the family was that it was some sort of special occasion when anyone spotted her outside her kitchen.
She married at 17 and spent 70 of the next 75 years of her life turning ingredients that were attractive all-you-can-eat buffets for microbes into the most delicious food, which again came with a ticking clock to microbial armageddon.
In the early days, they couldn’t afford a fridge, and once they could, her husband — who likely didn’t know where the kitchen was located — decided that fridges encouraged the consumption of stale food and were thus verboten in his kingdom.
I suspect this story of my grandmother’s life is far from being unique in India. But know what? The foundations of this story are not rooted in science. It’s a myth.
There is a tendency in patriarchal societies to resist technological breakthroughs that make life easier for women.
My grandfather’s father resisted the introduction of the pressure cooker, a device that made cooking rice and pulses convenient and gave back to the woman of the house the one thing that generations of husbands never did: time to do things other than cooking. His argument was the usual one against change when it comes to food —“Why change what has worked for centuries?”
If it was the pressure cooker in my great grandparent’s generation, it was the fridge in my grandparents’ generation. Make food and store it in a fridge? OH NO, IT WILL LOSE ALL NUTRITION, they will bemoan. And here’s where they are wrong.
Make no mistake: Food does not lose nutrition when refrigerated (*conditions apply).
Let’s understand how the device works first.
Life, it turns out, prefers a narrow range of warm temperatures. As the mercury dips, biological activity slows down. Enzymes don’t function, reactions don’t happen, and at about -18 C, everything stops.
Your refrigerator uses a simple heat-exchanger mechanism to remove heat from the inside of the fridge to the vents at the back. This keeps the inside of your fridge between 2-5 Celsius (and your freezer at -18 C).
One side effect of doing this is that the inside of your fridge is also pretty dry, moisture-wise.
This might seem counter-intuitive because there seems to be moisture on the surface of everything you store inside, but that’s just condensed water from your food. The actual humidity inside your fridge is very low.
This is important because microbes like two things: warm temperatures and high humidity. Your fridge is the opposite of both. Meaning microbes don’t get what they want inside the fridge.
This is why refrigeration matters in the modern food environment. Without refrigeration, the planet will likely waste more than half of the food it produces. Without refrigeration, most people on the planet will likely starve. Without refrigeration, even the rich middle class will not even have access to the diversity of things we eat today, especially if you live in a city.
Sure, technically speaking, you can move to a village and eat entirely local, freshly grown food all the time, but I guess most people can’t really do that.
Now let’s address the elephant in the room: nutrient loss.
What happens when you pluck a cucumber from its plant?
A clock starts ticking.
The vegetable (which is still living, unlike meat, whose cells die when the animal dies) is now all on its own in trying to prevent bacteria and fungi from devouring its resources.
Since plants can’t move, they use biochemistry to defend themselves. Onions do acid attacks on our eyes, chillies produce a molecule that creates the illusion of a burn, and spices produce essential oils that are lethal to microbes and insects.
But given enough time, the microbes will always overwhelm your food and win. The entire point of a refrigerator is to slow this down so that it gives you more time to use up your food. (I assume your generally charitable nature does not extend to freely feeding homeless bacteria and fungi.)
The next question is: what nutrients do we lose when we refrigerate food? It turns out, not much really, at least up to four to eight days.
This brings us to the woolly mammoth in the room that we ignored in favour of the tiny elephant. It’s cooking that causes nutrient loss — not refrigeration.
Water soluble vitamins (like B and C) and a few antioxidants in fresh produce are the most sensitive to heat. It is cooking that causes the most amount of “nutrient loss”, but then again, most foods are inedible when uncooked.
So stop obsessing over the idea of nutrient loss at an ingredient level and focus instead on what our lunch plate looks like. If it has a mix of cooked and uncooked food, a good amount of green vegetables and enough protein, you are doing good.
And guess what, if bacteria started eating your vegetables because you didn’t store them at 2-5 C, then you will likely be eating something that will cause food poisoning. Almost all food will attract pathogenic microbes at room temperature.
A fridge is a solid stone wall around your food. The microbes will eventually scale this wall as well, but it takes them time (3-4 days), and you get to enjoy your food safely in that time frame.
Refrigeration matters even more when it comes to major sources of protein. Without a fridge, you’d have to go and get meat from a butcher just before you cook because, unlike plants, dead animals are even more attractive to microbes because their cells have zero defences (because in animals, defence is not local but centralised in an immune system that requires blood circulation to reach points of infection, and in general, dead animals do not have circulating blood).
If you don’t eat meat, you likely get your protein from dairy, which, again, is notoriously prone to spoilage. Without refrigeration, India wouldn’t have had the white revolution, which people tend to think largely produced cutesy pop culture puns from Amul, but behind the scenes, it made a massive change in the amount of protein and fat the average Indian was able to get from dairy products.
In short, the India growth story of the last two decades would not have been possible without milk refrigeration.
So, how do you store stuff in the fridge in the best possible way? It’s quite simple.
If it’s fresh produce, it needs to be stored in closed containers or pouches that have some air gaps. Most fresh vegetables will rot if there is no air exchange (remember, they are still living things).
Cooked food, however, is pretty dead, so it’s best stored in air-tight containers. A lot of Indian food is sour, salty, and spicy (essentially designed to last at room temperature at least from lunch to dinner) and thus will last four to eight days quite easily.
There are a few exceptions like steamed white rice which is best consumed within a day or two. As a general rule, sour and spicy dishes last the longest in the fridge because acids and the antimicrobial nature of spices add another layer of protection. Blander foods tend to last much less.
When you take cooked food out of the fridge, remember that reheating it is going to reduce micronutrient content, particularly B and C vitamins.
In general, microwaving is a better option than heating on a stove because, unlike a stove that puts out uneven heat delivered to your food via a really hot piece of metal, a microwave oven only heats up the water inside your food and is just ideally suited to reheating cold food.
And again, don’t break your head about “nutrient loss”. A side salad with your reheated food and a squeeze of lime on yesterday’s reheated dal will replenish the Vitamin C you likely lost to heat and time.
If your fridge compartment can help you store cooked food for up to a week, your freezer can help you store food for up to six months or longer. At -18C, biological activity stops, so what you put into the freezer is also technically frozen in time.
Fun fact: Frozen peas are often fresher than fresh peas because if you live in a city, your peas likely travelled a long distance and were thus plucked at suboptimal ripeness to survive their long journey. Frozen peas, on the other hand, are typically plucked at peak ripeness and, thus in many situations, are at least as nutritious, if not more nutritious, than “fresh” peas.
The one bit of physics you need to keep in mind, though, is that ice occupies more volume than liquid water and thus when you freeze fresh produce, ice will likely damage some cells as it expands.
This means that once you take stuff out of the freezer, it will start to degrade faster than the stuff you take out from the regular fridge compartment. So always use up things you take out of the freezer quickly.
Well, there you go. Using a fridge smartly actually helps you eat healthier because you get to eat a greater diversity of things whenever you want.
Food does not lose nutrients at low temperatures. Frozen food is absolutely nutritious. Never underestimate the power of convenience when it comes to attaining your family’s health goals. The fridge is your closed-door Ladakh. And Ladakhi food is astonishingly delicious.
And finally, don’t romanticise my (and your) grandmother’s lives when it comes to slaving in the kitchen. Please.
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