What is the Best Way to Preserve Strawberries

8-9451

Grade 8

Nativity Catholic School

Archdiocese of San Francisco

2024 San Mateo County Office of Education STEM Fair

Abstract

The purpose of my project is to identify ways to best preserve strawberries from mold growth. In my research I learned that mold spores likely already exist on most berries, mold prefers warmer temperatures and moisture for growth, and hot temperatures can kill mold spores. My hypothesis is that washing berries, storing them in a refrigerator, or soaking them in hot water can help slow mold growth, but which is the most effective? My independent variables were the storage temperature, washing or not, and soaking the strawberries at various temperatures. My control constant variables were the temperature of the refrigerator, the temperature and location for those at room temperature, the sealed containers to store them, and the strawberries all came from the same batch. My dependent variables were the number of strawberries with mold and the length of time. I checked the berries on the daily basis, looking for any signs of mold. If I saw even a little bit of mold, I marked the berry as having mold. The data showed that mold grew twice as fast on the room temperature berries versus the berries stored in the refrigerator.The results generally aligned with my hypothesis. The berries stored in a cold refrigerator lasted more than twice as long then the room temp samples. Washing didn’t help as much as I expected. I think this is because mold needs moisture and warmth to survive, and even though I dried off the strawberries there must have still been some water on them. Finally, soaking berries in hot water for a short period of time also helped slow mold growth.

Purpose Statement

I love to bake, and sometimes my recipes call for fruit, including strawberries. But when I go to get fruit from the basket in the kitchen or the refrigerator, it its been there for a few days, it's often moldy. Unfortunately, fruit does not lasts long.

This issue led me to the idea of this project: what is the best way to preserve strawberries.

I did research online to learn about mold and what causes it to grow. I used this information along with other web sources to come come up with experiments to figure out the best way to make fruit stays mold free as long as possible. I hope my results will show how to properly store strawberries so they last longer.

Hypothesis

In my research, I learned that mold are microscopic fungi that live on plants. They are likely already on strawberries when you buy them. I also learned mold needs warmer temperatures and moisture to grow and that high temperatures kills mold spores.

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My hypothesis is that the best way to preserve strawberries will be washing them, drying them and storing them in the fridge. I think this will preserve the strawberries the best because washing them removes the spores that are already there, drying them will be necessary because mold likes moisture, and since mold prefers warmer temperatures, colder temperatures should slow down growth.

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In addition, I plan to soak some strawberries in hot water for a short period of time. In my research, I read about Thermotherapy which is the process of exposing fruit to hot water. I also want to test that if hot water kills mold spores, it should also help slow down any mold growth.

Experimental Procedures and

Materials

• 72 Strawberries – 9 each for each experiment. Same brand, bought at the same time
• 8 containers with lids
• Strainer
• Pot to heat water
• Thermometer
• Digital stopwatch

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• Slotted spoon
• Tongs
• Paper towels (1 roll)
• Sticky notes or Masking tape (1 roll)
• Disposable gloves (1 box
• Notebook

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Experimental Procedures and

Materials

Procedure:

• Place all of materials out on a flat surface.
• 9 different experiments using UNCUT strawberries.
• At Cold Temperature:
• Place 9 strawberries as is in a sealed container, label and store in fridge.
• Wash 9 in tap water for 30 seconds, dry and place in sealed container, label and store in fridge.
• Wash 9 in tap water for 30 seconds, place in sealed container, label and store in fridge.
• At Room Temperature:
• Seal 9 strawberries as is in container and label.
• Wash 9 strawberries in tap water, dry, seal and label.
• Soak 9 strawberries in 125 degree water for 45 seconds, dry, seal and label.
• Soak 9 strawberries in 125 degree water for 3 minutes and dry, seal and label.
• Soak 9 strawberries in 140 degree water for 45 seconds and dry, seal and label.
• Store room temperature samples in a dark area of house.
• Make sure each experiment is clearly marked for proper identification.
• Observe daily and record # of berries with mold.

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Experimental Results - Raw Data

Experimental Results

Cold and Room Temp

Experimental Results

Cold Temp (37 deg F)

Experimental Results

Room Temp (~67 deg F)

Experimental Results

Pictures - taken on 12/21/2023, 10 days after I started.

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D

G

F

H

B

C

A

E

B

Analysis of Experimental

Results

The colder environment was better at slowing mold growth. All 3 cold samples went at least 9 days without mold. The first room temp sample had mold after one day and all room temp samples had mold after 4 days. This was twice as fast as the cold samples.

In the cold environment, the sample with nothing done to it lasted the longest without mold. The washed samples got mold sooner. I suspect it is because they were not fully dried as the “as is” sample that I did not wash.

In the room temperature samples, the sample that was soaked in 125 degree water for 45 seconds was the slowest to grow mold. The worst cases of mold growth were room temperature as is, and room temperature washed and dried. All room temp samples that were soaked in hot water, mold grew more slowly.

Conclusions

Cold temperature samples went without mold for more than twice as long as the room temperature samples. This aligns with my hypothesis that mold thrives in warm environments. But the cold temperature samples that were washed got mold faster. This was not what I expected. I thought washing would help by removing spores. I think this is because I probably did not wash all the spores off and even though I dried them as best I could, there was still some moisture on the berries. Mold needs moisture to grow.

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The room temp samples grew mold much faster as expected. And the Thermotherapy apparently helped slow mold growth. All room temp samples that were soaked in hot water showed slower mold growth.

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This results aligned with most of my hypothesis . The cold temperatures slow mold growth. Washing didn't remove mold spores but when they aren't fully dry the remaining moisture can still help mold growth. Thermotherapy kills mold but it also needs to be dried as much as possible.

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As I did the experiment I had additional questions. If one berry got mold, would the others get it faster? And how would this affect blueberries or different kinds of berries. And one of the thermotherapy samples had a lot of liquid in the container afer a few days. Not sure what this was or what caused it.

Acknowledgements

I would like to thank my dad for helping me through my experiment and collecting the data. I would also like to thank my mom for helping me come up with my experiment and spell checking my slides.

Bibliography and

Sources

Science Buddies Staff. (2020, June 23). Save Those Spoiling Strawberries! https://www.sciencebuddies.org/science-fair-projects/project-ideas/FoodSci_p064/cooking-food-science/save-those-spoiling-strawberries

Alice Callahan. (2022, March 7). Will One Moldy Berry Ruin the Rest? https://www.nytimes.com/2022/03/07/well/eat/berry-mold-spoil-box.html

Harold McGee. (2009, August 25). Prolonging the Life of Berries https://www.nytimes.com/2009/08/26/dining/26curi.html?_r=3&em

Lois Tilton. (2009, June 5). Botrytis Mold of Strawberries https://davesgarden.com/guides/articles/view/1302/

What is Berry Mold?

In my research I learned some interesting facts about mold:

• Molds are microscopic fungi that live on plant or animal matter. They can be found indoors and outdoors and are part of our natural environment.
• The most common disease of strawberries is gray mold, caused by the fungus Botrytis cinerea.
• Molds on berries are usually not harmful, even accidentally eating a moldy berry, so it should not make you sick, but it would have a bad flavor.
• Mold spores are everywhere. They’re probably there in small amounts on most fresh produce we eat.
• In a New York Times Article I read molds become more dangerous when they grow deeper into food. This is when some types of mold can produce toxins. This doesn’t usually happen with berries based on the types of molds that grow on them, but it does happen with larger foods that are moist or have a soft texture, like leftover meats or casseroles, jams and jellies, soft cheeses and breads. So be sure to throw these out if you see mold on them.
• The same NYT article says mold can survive on surfaces, so keep your refrigerator clean to “break the mold spore cycle”.