Kitchen Science for Kids: Food Waste Audit

Most young kids understand—better than some adults—that we have only one planet and so should preserve it rather than trash it. Curious and inquisitive, they are also natural scientists. In this kitchen science for kids lesson plan, your kids will learn about food waste—why we waste food, what else we waste when we waste it, what happens to our food waste—and think up ways to reduce it. I can’t guarantee your household food waste will go down to zero but I am confident that after completing this lesson, you’ll say to your children much less often, “Don’t waste food. Some people don’t have enough to eat!” In fact, your kids might remind you of this!

fresh produce
Too tasty to waste

In this lesson, your kids will learn

  • Math
  • Science
  • Vocabulary
  • Following directions

Time requirement

You can audit your waste for a couple of weeks, a couple of months or longer.


Anaerobic bacteria: noun Bacteria that can survive and reproduce in an environment that lacks oxygen.

Bacteria: noun Microscopic, single-celled organisms that live in soil and water and on plants, animals and other matter. Their purpose in life is to reproduce.


1 noun A mixture largely of decayed matter of once living things (as grass) or their products (as coffee grinds) and used for fertilizing and conditioning land

2 verb To convert (a material, such as plant debris) to compost (Merriam-Webster)

Decompose: verb

1 To separate a thing into its parts or into simpler compounds <decompose water into hydrogen and oxygen>

2 To break down through chemical change : ROT (Merriam-Webster)

Greenhouse gas: noun Any of various gaseous compounds (such as carbon dioxide) that absorb infrared radiation, trap heat in the atmosphere, and contribute to the greenhouse effect (Merriam Webster)

Humus: noun A brown or black product of partial decay of plant or animal matter that forms the organic portion of soil (Merriam Webster)

Landfill: noun

1 A system of trash and garbage disposal in which the waste is buried between layers of earth

2 An area built up by landfill (Merriam-Webster)

Methane gas: A greenhouse gas 25 times more potent than carbon dioxide (Essential Environment, 4th ed., Withgott J., and Laposata M., Pearson 2012)

What’s the big deal over wasting food?

The following statistics on food waste come from the National Resources Defense Council.

Producing food in the US:

  • Accounts for 10 percent of the total energy budget
  • Uses 50 percent of land
  • Accounts for 80 percent of all freshwater consumed

Amount of food and other resources wasted:

  • 40 percent of food in the US goes uneaten
  • That’s 20 pounds per person, per month
  • We toss $165 billion worth of food per year
  • This wastes 25 percent of all freshwater, chemicals, energy and land


  • 1 in 6 Americans is food insecure
  • A mere 15 percent of this wasted food could feed 25 million Americans every year

Why do we waste so much food?

1. Buyers consider some produce “ugly.” Most grocery stores will accept fruit and vegetables only if they meet rigid cosmetic standards. Everything has to have the same shape, the same size and zero blemishes. Even bananas require a certain angle to their curve to be accepted.

2. Pickiness. We tend to eat certain parts of animals or vegetables and waste the rest. Farmers can easily sell their lamb chops but many people don’t want to eat any other part of the animal. This can result in a lot of waste. 

3. Confusion over expiration dates on packaged food. The US government does not regulate these dates. The food manufacturers stamp them on as a guideline. They say things like “best-by,” “use by,” “sell by” or “best before.” People throw a lot of perfectly good food out because they’re confused by these labels. Generally, these dates indicate how long the food will remain in its highest quality. If it’s unopened, it will last longer.

4. Other factors. Simply buying more than we can eat or improper storage can lead to food waste. Refrigeration can render tomatoes mealy and tasteless, which can lead to waste. (Click here for more on storing produce.)

What happens to food in a landfill?

In a landfill, food becomes compacted along with all the other waste, and doesn’t come into contact with oxygen. Cut off from oxygen, anaerobic bacteria decompose the food. This type of bacteria releases methane gas as a byproduct of decomposition. Methane gas, a greenhouse gas that warms up our atmosphere, is is 25 times more potent than carbon dioxide, the greenhouse gas you hear about the most. All of the food wasted in the United States accounts for about 25 percent of the methane gas emissions, according to the NRDC.

In a properly maintained compost pile or bin, on the other hand, food comes into contact with air, and while it decomposes, it produces dramatically fewer greenhouse gas emissions. Composted food breaks down into humus, the most basic compound in soil. Compost has the added benefit of helping capturing carbon dioxide from the air and storing it in the soil, rather than letting the greenhouse gas escape into the atmosphere.

vegetable broth from scraps
Vegetable scraps simmering in water for free vegetable broth


You’ll go through the following steps:

  1. Measure food waste
  2. Analyze your data
  3. Plan on how to reduce food waste

Repeat 1 through 3 and track your progress

1. Measure food waste
Fillable worksheet

Click here to download the worksheet pictured (right). Fill in the fields. You may want to fill a worksheet out every day, depending on how much you waste, or tally everything once a week. You will address the following:

  • What did you waste?
  • How much did you waste?
  • Approximate cost of the food you wasted
  • Reason for wasting
  • Ideas to reduce waste in the future
2. Analyze your data

Graph how much you wasted. After a couple of weeks, you should have enough data to create a graph of what you wasted. You could make a bar graph, a line graph, a pie chart, even a Venn diagram. The examples down below will give you some ideas of what to plot on your graphs.

Think about:

  • How much you wasted (by weight)
  • The cost of how much you wasted (approximately)
  • Which foods you waste the most
  • Why you waste food (you may notice a pattern)
Food in pounds wasted every week
Types of food wasted in pounds per type
Pie chart of types of food wasted
I have a hypothesis that a lot of processed food (almost always packaged in plastic) goes to waste
3. Plan on how to reduce food waste

Completing step two will help you figure out which areas you need to work on. For example, you may discover that you waste a lot of bread. You could buy less bread, freeze some of your bread while it’s still fresh or make bread crumbs, French toast or bread pudding out of your stale bread.

Here are some ideas for reducing food waste:

  • Buy less food
  • Buy less of the food that goes to waste the most
  • Plan meals in advance
  • Cook smaller portions
  • Cook food that people want to eat
  • Snack on perishable food first, such as fresh fruit and vegetables
  • Get creative with leftovers
  • Store food properly as soon as you bring it home
  • Use vegetable scraps and bones for broth
  • Learn how to preserve food (click here for a post on fermentation)
  • Compost what goes to waste (click here for a post on simple composting)
Limp vegetables? Insert in a jar of water for a day


Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming, edited by Paul Hawken

National Resources Defense Council

If you like this lesson plan, here is another on sourdough starter. Kids will learn about biology, history and more right in your kitchen.

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