Are Red Apples Sweeter Than Green Apples?

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Author: Christine Ryder Combs
Difficulty of Project (Easy, Medium, Hard)


Grade Level (Elementary, Middle, High School)

Middle School

Cost (Approximate Cost)


Safety Issues

The project requires the use of a sharp knife to cut apples a designated supervisor such as a parent or guardian should supervise this project.

Material Availability

Materials such as the apples are readily available at the grocery store and pH strips can be purchased from chemical supply company or local hardware store.

Approximate Time Required to Complete the Project (Hours, days, weeks?)

1 – 5 days


To obtain quantitative evidence to support the age old myth, red apples are sweeter than green apples.

The project goals include identification of the pH for apples of varying shades of red and green and to relate the pH of the apples to their sweetness.

Materials and Equipment / Ingredients

 pH paper

Green apples

Red apples

Yellow apples


The pH of a substance is a measure of a substances hydrogen ion concentration. With increased hydrogen ions, the substance becomes more acidic. Acidic substances are characteristically sweeter than less acidic substances. The pH of a substance ranges from pH 1 through 14, with acids characterized by a pH between 1 and 7 and alkaline compounds characterized by a pH between 7 and 14. In this experiment it is proposed the sweeter the apple the more acidic the apple and the lower the pH of the apple.

Research Questions

What substances make up organic fruit and vegetables?

What is the nutritional difference between red and green apples?

What makes a substance sweet?

How can sweetness be measured?

What is the pH scale?

What is hydronium ion concentration?

Terms, Concepts and Questions to Start Background Research

Hydronium ion

Experimental Procedure

  1. Select at least five different apples for the purpose of testing. The apples should be light green, dark green, light red, dark red and yellow.
  2. Select two apples of each color for experimentation.
  3. Slice each of the 10 apples.
  4. Place a strip of pH paper on the surface of the apple slices. The pH paper should stick to the inside of the apple and change color in response to the apples wet interior. Do not place the pH paper on the outside skin of the apple. The outside skin of the apple is dry and will not change the color of the pH paper.
  5. Record the shade of the apple and its corresponding hydronium ion concentration, pH.
  6. Repeat the experiment to record the hydronium ion concentration or pH of other slices from the same apple and the pH of the second apple of the same color.


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