Grade Level: 4th - 7th; Type: Food Science
The goal of this experiment is to explore non-chemical means of preserving fruit. Students will learn about mold and how to prevent the formation of mold in berries.
- Can heating strawberries prevent the formation of mold?
- What is thermotherapy?
- Is there any optimal temperature for prevent molding without damaging the strawberries?
- Can this process be repeated on other fruit?
- What is mold and where does it come from?
Everyone is familiar with the moldy strawberry phenomenon in which you go to the fridge seeking the strawberries you purchased yesterday only to find they’ve gone moldy. Food scientist Harold McGee explored different ways to prevent this from happening. He subjected strawberries to heat as he tried to determine what temperatures were so extreme that they made the berries unpalatable, and what temperatures prevented future mold by killing the mold spores resting on the berries. According to McGee, mold can be prevented without destroying the fruit. McGee coined the phrase “thermotherapy” to describe the process of subjecting berries to heat to prevent mold. McGee’s experiments are worth repeating, trying different berries and different temperatures.
Most supplies are probably already available at home or the grocery store. See if you can borrow a good thermometer from school.
- Access to a stove
- Large saucepan
- Four boxes of fresh (not frozen) strawberries
- At least one – and preferably two - of the following: box of blueberries, raspberries, blackberries (optional)
- Lab-quality thermometer that accurately measures between room temperature and 150 degrees Fahrenheit.
- Plastic berry boxes
- Plastic wrap
- Put ten strawberries in a plastic berry box. Cover with plastic wrap. Label these “Control” and set aside.
- Put ten strawberries in a plastic berry box. Fill the saucepan with water. Using a thermometer, heat the water to 110 degrees. Using tongs, submerge the strawberries for 30 seconds. Remove the berries and cover with plastic wrap. Label these as “110/30” and set aside. Do these berries seem edible or were they destroyed by the heat?
- 3. Repeat step #2, heating the temperature to 115, 120, 125, 130, 135 and 140 degrees. Make sure your berries are appropriately labeled. Each time, make a note regarding the relative edibility of the berries. Store each other separately, which each group of berries several feet away from the other batches.
- Check on your strawberries every 12 hours. How many berries were moldy? Graph the number of moldy berries as a function of time. Create a chart that describes how the berries were treated, the date, and your observations. What is the optimal temperature that provides the maximum protective benefit without destroying the berries?
- Repeat the experiment with another type of berry. How sturdy are your new berries compared to the strawberries? Is the optimal temperature the same?
Terms/Concepts: Mold; Thermotherapy; Spores
New York Times: Prolonging the Life of Berries by Harold McGee. 8/25/09
Dave’s Garden: Botrytis Mold of Strawberries