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Why do Fruits and Vegetables Get Soft When Cooked?

Why do fruits and vegetables get soft when cooked? This post explains this food science for kids, along with a couple of experiments to try!

Food Science for Kids: Why do Fruits and Vegetables Get Soft When Cooked?

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This month I’m participating in the 2017 Storybook Science Series hosted by Inspiration Laboratories. This week’s theme is Kitchen Science, which we are pretty fond of in our house. I picked Pretend Soup as the book, and I’m writing about one of the questions I find my kids asking as we cook together: why do fruits and vegetables get soft when cooked?

Food Science for Kids: Why do Fruits and Vegetables Get Soft When Cooked?

My daughter Emma first asked me this question when we were making the carrot pennies recipe from Pretend Soup. I think she was four years old at the time. Pretend Soup is a wonderful first cookbook for kids. Each step is illustrated, so that even pre-readers can follow the recipes. The recipes are also pretty healthy.

I gave Emma a simple answer, along the lines of “the fruits and vegetable cell walls break down, and that makes them get soft.” That satisfied her curiosity, for the moment, but this question recently returned in our home, and I did some extra research.

Why do Fruits and Vegetables Get Soft When Cooked? Let’s Look at Hemicellulose

It turns out that almost all plant walls include a kind of carbohydrate called hemicellulose. The hemicellulouse structure isn’t very strong. It breaks apart in response to the heat. However, hemicellulose won’t break down in a highly acidic environment. So, if you try cooking vegetables in vinegar or start cooking vegetables in a strong (acidic) tomato base, they may not actually get soft

Hemicellulose is also part of the reason ripe fruit is softer while unripe fruit is hard. As a fruit ripens on the tree, both hemicellulose and pectic substances break down, convert to water-soluble pectins, and dissolve. This makes the fruit soften. Adding sugar to sliced fruit slows down this process. So, if you have very ripe fruit, add a little sugar to keep it from breaking down too quickly in the oven (or even in a salad, on a warm day). If your fruit is under-ripe, cook it first to allow the pectic substances and hemicellulose to break down to just the right softness before adding sugar.

Isn’t science fascinating? You can find more fascinating scientific activities inspired by children’s books here:


I love activities like this exploration of why fruits and vegetables get soft when cooked that can be done using items we already have in our homes. Check out this collection of STEM activities for kids using household items. I also have a post dedicated to baking with kids in the kitchen. Do you have an activity you think we will enjoy? Please share any ideas you have on my Facebook page, or tag me on Instagram

MaryAnne at Mama Smiles
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MaryAnne is a craft loving educator, musician, photographer, and writer who lives in Silicon Valley with her husband Mike and their four children.

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