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How Does Osmosis Help Us Cook?

From boiling to curing to pickling, osmosis and salt helps us make food every day!

Osmosis is a biological process involving the movement of water. Salt influences osmosis, allowing it to be used in cooking.

Table of Contents

How does osmosis work?

Living systems love equilibrium. Equilibrium is a state in which opposing forces are balanced. Think about a weighing balance. On one side is a large pile of building blocks. On the other is just a single block. Living systems – from a single cell to a fungus network, to a human body or a blue whale, absolutely hate this unbalanced state. They are much happier with an equal number of blocks on both sides.

These blocks represent molecules of different compounds. One of the most abundant molecules is water! The balance represents a semipermeable membrane. A semipermeable membrane is a thin layer that allows some substances (like water, oxygen, and carbon dioxide through) and prevents other substances (larger molecules like proteins and carbohydrates) from passing through. It’s like a net, with holes that allow small things to pass through.  Living systems want an equal number of water molecules on both sides of the balance. This is the driving force behind a process known as osmosis. Osmosis is the movement of water molecules across a semipermeable membrane.

osmosis
The diffusion of water through a semipermeable membrane down its concentration gradient. Image Credit : OpenStax

As strange as it is to imagine, all foods are made up of cells that have a semi-permeable outer membrane. Fruits, grains, nuts, and seeds are made of plant cells. Meats are made of animal cells. The movement of water in and out of the cells which make up our food is what helps cook them.

Simple_diagram_of_animal_cell
This is an animal cell. The cell membrane is semipermeable. Image Credit: domdomegg

Does salt make water boil faster?

It’s a common misconception that adding salt to water can make it boil faster. The theory is that it lowers the boiling point of water, so less heat is needed to make the water boil. However, in order for this to be true, water needs to be about 20% salt solution. This means that a 100-gram salt-water mixture needs to be 80g water and 20g salt. This is incredibly salty! Imagine cooking vegetables in water that is saltier than the ocean. Heating a big pot of water and adding a teaspoon of salt unfortunately won’t help it cook any faster, but it can help with other things.

What does salt do to food?

Imagine our weighing balance again. Instead of a pile of water molecules on both sides, you have two glasses. Both have twenty molecules of water. You then add 10 molecules of salt to one side. Although the number of water molecules is the same on both sides, the concentration of water becomes a lot lower when you add salt. 

Salt causes water to rush out of food. It lowers the concentration of water outside of the semipermeable membranes that make up food, and the water leaves the food.

How can osmosis be used in cooking?

One of the most ancient ways osmosis is exploited in cooking is in a process known as curing. In curing, meats or eggs are submerged in a dry salt-sugar mixture. The water leaves the food. Without water, bacteria cannot grow. Bacteria is what causes food to go rotten, so when the bacteria are killed, food stays fresh for much longer.

Pickling is a very similar process to curing, but instead of a dry mixture, foods are submerged in a very concentrated salt solution. Ancient civilizations have made use of curing and pickling for millennia. By preserving meat and vegetables, they could consume foods out of season or when resources were low.

pickled vegetables
An array of pickled vegetables. You can pickle almost anything!

Although salting water to make it boil faster doesn’t quite work, salting the water can do something else. When vegetables are boiled and floating in salty water, the water inside the vegetables wants to go out, and the salt outside the vegetables wants to go in.

Salting can even help you make extra-crispy fried vegetables or potato chips. When you salt vegetables prior to frying them, you draw out all the water through osmosis. If you fry it after, the loss of water makes it extra crispy.

It even works for marinades! When you soak your meat in a mixture of salt and flavors, the water from the meat wants to come out and the flavors go in. Some people exploit this even further. Try it next time you marinate vegetables or tofu (not meat!). Taste a little bit of the marinade four or five hours after you put the food in. It’ll taste less flavorful and more watery. Don’t worry, this just means the food you want to cook will taste even better!

Lamb_marinated_in_Cabernet_Sauvignon
Pieces of lamb being marinated in a sauce. Image Credit : Dplanet

The next time you are cooking or if you see someone whipping up something exciting in the kitchen, think about how osmosis might be involved. Are they curing, pickling, boiling, or frying? Where might the water be coming from or where could it be going? Is there any way you can use osmosis to make cooking faster, and the food more flavorful?

Glossary

Curing: A process of submerging food in dry salt to draw all the water out and preserve it

Equilibrium: A state of balance between two opposing forces

Osmosis: The movement of water molecules across a semipermeable membrane

Pickling: A process of submerging food in concentrated solutions to draw all the water out and preserve it

Semipermeable membrane: A membrane that only permits certain substances through

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Author

  • Yamini's (he/they) interests lie in environmental education, science communication and trying to build a better world. When not languishing in front of his laptop, they can be found outside, poking at any insect, bird or plant. They love making science accessible, especially to those who aren't encouraged to pursue it. Yamini hopes that the young women who read Smore love learning from their articles and get just a little bit more excited about science!

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