Why freezing often ruins the texture of food

HostWe have all had that letdown where we pull a bag of strawberries out of the freezer, let them thaw, and end up with a pile of mush. They still taste like fruit, but that fresh crunch is just gone. It feels like the cold actually broke the food. Why does putting things in the freezer end up ruining how they feel in your mouth?

GuestIt's because water is one of the only things in the world that gets bigger when it freezes. Most things shrink when they get cold, but water does the opposite. It grows. Think about what food is made of. Most of it's just water held inside tiny little bags called cells. When you put a strawberry in the freezer, the water inside every single one of those tiny cells starts to turn into ice. As it turns to ice, it expands. It's like putting a glass bottle of water in the freezer with the cap on tight. Eventually, the pressure is too much and the glass cracks. In your food, the ice crystals act like tiny knives. They grow and stretch until they poke holes right through the walls of those cells.

HostSo when the food thaws out, the water just leaks out of all those tiny holes?

GuestThat's it. All the structure that makes a fresh berry firm is gone. The water that used to be held tightly inside the cells is now just sitting there, which is why you get that puddle of red juice at the bottom of the bowl. The fruit has basically turned itself inside out. This is a huge deal for plants especially, because plants rely on those stiff cell walls to stay upright and crunchy. Once those walls are popped by the ice, there's no way to fix them. You're left with a wet, soft mess because the skeleton of the plant has been shattered on a level so small you can’t even see it.

HostIf this happens to everything, why can I freeze a steak and have it come out tasting mostly fine, but a salad would be ruined?

GuestMeat is built differently. Animal cells are more like flexible balloons than the stiff boxes you find in plants. They can stretch a bit more before they pop. Plus, meat has a lot of tough protein fibers that don't mind the ice as much. But even with meat, you can still see the damage. If you ever thaw a piece of chicken and see a lot of pink liquid in the package, that's the same thing. It's the water escaping from the cells that were damaged by the ice. The reason a salad is a total loss is that lettuce is almost all water and very thin walls. There's nothing there to hold it together once the ice does its work.

HostIt seems like the ice is the real enemy here. Is there any way to freeze things without those ice knives growing so big?

GuestThere's, and it all comes down to how fast you can get the food cold. If you freeze something slowly, like in your freezer at home, the ice has a long time to grow. The crystals can take their time and build up into long, jagged shards. Those are the ones that do the most damage. But if you can freeze food very fast, which is what big food companies do, the ice doesn't have time to grow big. Instead of a few big knives, you get millions of tiny little ice grains. They're so small they don't pop the cell walls. This is why a bag of frozen peas from the store often stays pretty firm. They were flash frozen in a matter of seconds.

HostI don't really see how the speed changes what the ice looks like. If it reaches the same cold temperature, shouldn't the ice be the same?

GuestYou would think so, but ice is a bit like a crowd of people trying to get into a theater. If everyone walks in slowly, they can form long, organized lines. That's like the big ice crystals. But if everyone rushes the door at once, they just end up in a big, messy jumble right where they are. In flash freezing, you take the heat away so fast that the water bits don't have time to find each other and build those long, sharp lines. They just freeze right where they're in tiny clumps. Because they're small and blunt, they don't poke through the cell walls. Your home freezer is just too slow to do that. It takes hours to get to the center of a pack of meat, and in those hours, the ice needles are just growing and growing.

HostSo that explains the mushiness. But sometimes I find something in the freezer and it's the opposite. It’s dry and tough and tastes like the freezer itself. That doesn't sound like cell walls popping.

GuestThat's freezer burn. It's actually a kind of drying out. Even when things are frozen solid, the water can still move. It does this weird thing where it skips the melting part and turns straight from ice into a gas. The water on the surface of your food slowly floats away into the dry air of the freezer. It leaves behind these dry, leathery pockets. It's almost like the food is being turned into jerky while it's still cold. The reason it tastes bad is that those empty pockets now have room for air to get in, and the air starts to break down the fats and the colors in the food.

HostIt sounds like we're in a constant battle with water moving around where we don't want it. Is there any food that's actually safe from this?

GuestHigh sugar or high salt helps a lot. Think about ice cream. It's full of sugar and fat. The sugar gets in the way of the water bits when they try to link up to make ice. It acts like a kind of antifreeze. That's why ice cream stays soft enough to scoop while a bag of peas turns into a solid brick. The sugar keeps the ice crystals so small that you can't even feel them on your tongue. If those crystals ever do get the chance to grow, like if your ice cream melts a bit and you freeze it again, that's when you get that gritty, sandy feel. The ice knives have finally won.

GuestThis is the same reason we can't freeze people and wake them up later because our bodies are too big to freeze fast enough to stop those ice needles from wrecking our brains and hearts.

HostThe strawberries in my kitchen are a much smaller problem than that, but they both show just how much power a little bit of growing ice can have.