Purpose

The purpose of this project is to see if washing your rice a different number of times can affect its cleanliness and whether it has an impact on your body. Many people in the world eat rice, and if not washed properly, there is a potential risk of harming the body. I would like to see if there are different amounts of bacteria in rice that is washed a different number of times.

Hypothesis

I believe that washing the rice until the water is clear will be the most effective option, since if the water has no dirt or cloudiness, it indicates that the rice is almost completely clean. This gives me the impression that the starches, dust, and other microorganisms have been thoroughly washed away. My reasoning for this is that the more I wash the rice, the more unwanted impurities have been washed away.

Zero washes gives me the idea that the rice will still have specks of dust or other unwanted microorganisms. Since the water will still have cloudiness, it tells me that the rice has not been properly washed and is still dirty. Washing the rice once would only clean the outer layer, leaving dust particles or other microorganisms/bacteria behind.

What is the recommended number of times to wash your rice?

Based on my research, many websites have given me varying answers on how many times you should wash your rice. Since many of the websites provided similar answers, here are the top four average answers:

Additionally, I have asked friends and family how many times, on average, they wash their rice. I have received answers ranging from 3 times to washing until the water is clear. Based on the information I have gathered on how many times you should wash your rice, I will use this data to execute my project.

Why do individuals wash their rice?

Many individuals wash their rice for various reasons. Some for good measure, and others for safety concerns.

What kinds of unwanted materials or microorganisms are in unwashed rice and how can they affect your well-being?

There are several things in rice that individuals may consider unwanted:

Bacillus cereus bacteria (B. cereus) can be found in rice and can be consumed if not washed properly. B. cereus can enter rice through the soil. When rice is grown, there is a potential for B. cereus to be present in the soil. With the bacteria in the soil, its spores can come into contact with the rice, contaminating it.

It can survive harsh conditions, such as boiling temperatures or during harvesting. The active bacteria can be killed off, but the dominant spores of the bacteria can still remain in the rice, making it a hazard to your body. Fortunately, the B. cereus on the outer layer of the rice can be washed off. The more you wash it, the more Bacillus cereus can be removed.

If your rice is not washed properly, your body can be affected by symptoms such as vomiting, nausea, and diarrheal syndrome. This makes it important to wash your rice thoroughly.

Controlled variables

• 1 cup of white rice 
• Sufficient amount of water for cooking the rice
• Type of rice cooker
• Cooking time (44 minutes)
• Type of microscope
• Type of petri dish
• Type of nutrient agar solution
• Type of cotton swab
• Type of gloves

Manipulated/independent variable

• The number of times I washed the rice (once, twice, three times, four times, five times, until the water is clear)

Responding/dependent variable

• Different levels of cleanliness of the rice (Under a microscope and on a petri dish.)

Procedure for microscope testing

1. Gather materials for steps 1-2 (rice, rice cooker, and water).
2. Wash hands thoroughly before handling the rice to avoid adding any other bacteria to the samples.
3. Wash the different sets of rice:
   • Zero times (sample 0)
   • Once (sample 1)
   • Twice (sample 2)
   • Three times (sample 3)
   • Four times (sample 4)
   • Five times (sample 5)
   • Until the water is clear (sample 6)
   • Dry, unwashed rice (sample 7)
4. Cook the rice using the same amount of water and cooking time to ensure a fair experiment.
5. Wash the rice cooker after each sample to ensure the previous sample will not interfere with the next one (repeat for each sample).
6. Gather materials for steps 7-10 (microscope, gloves, all rice samples, phone, plastic bags).
7. Place the rice samples into different bags for each sample.
8. Bring the rice samples to school to access the microscopes.
9. Examine the rice samples under a microscope using gloves to handle the rice and avoid adding unnecessary bacteria.
10. Take pictures of the different rice samples under the microscope for observation.
11. Observe each magnified view of the rice samples.

Procedure for petri dish testing

1. Gather materials for steps 1-2 (rice, rice cooker, and water).
2. Wash hands thoroughly each time before washing the rice to avoid adding any other bacteria to the samples.
3. Wash the different sets of rice:
   • Once (sample 1)
   • Twice (sample 2)
   • Three times (sample 3)
   • Four times (sample 4)
   • Five times (sample 5)
   • Until the water is clear (sample 6)
   • Dry, unwashed rice (sample 7)
4. Cook the rice using the same amount of water and cooking time to ensure a fair experiment.
5. Wash the rice cooker after each sample to ensure the previous sample will not interfere with the next one (repeat for each sample).
6. Gather materials for steps 7-10 (petri dishes, all rice samples, phone, gloves, cotton swabs).
7. Use a cotton swab to collect a sample of the rice.
8. Use a brand-new cotton swab each time you collect a sample from a different batch of rice.
9. Use the cotton swab to gently streak it on the petri dish using a zig-zag pattern.
10. Repeat this process until all of the rice samples have been collected onto the petri dishes.
11. Write the date, seal, and label each petri dish (Example: February 2nd, 2025. Sample #3).
12. Place the petri dishes in an incubated space (For bacterial growth, the required temperature is 25°C).
13. Check the samples regularly to observe any bacterial growth.
14. Once bacterial growth is visible, take a picture of each petri dish.
15. Observe each sample.

Procedure for setting up the petri dishes

1. First, I gathered 750mL of purified water and 16 grams of nutrient agar to create a nutrient agar solution.

2. Next, I poured the 750 mL of purified water into a clean pot to ensure no bacteria would interfere with the experiment. I slowly added the nutrient agar to the pot of water, which helped prevent clumps from forming. Then, I gently stirred the nutrient agar powder into the water to avoid any accidents.

3. For the third step, I placed the nutrient agar solution on the stove and set the heat to medium-high to prevent the water from evaporating too quickly and to avoid burning the nutrient agar. Then, every minute, I stirred slowly to prevent clumps from forming. I continued this process until the nutrient agar solution began to boil.

4. Once finished, I set the nutrient agar solution aside to cool for 10 to 15 minutes. This allows the nutrient agar to slowly decrease in temperature and turn into a solution.

5. Once cooled, I poured the nutrient agar solution into the petri dishes until it reached ⅓ of the way up the dishes. This allows enough space for bacteria to grow without coming into contact with the lid. With too much agar, it can interfere with the growth of the bacteria.

Procedure for growing bacteria using a petri dish (With pictures)

1. First, for each petri dish, I collected a sample from each rice sample with a sterile cotton swab. Once I had completed that, I swabbed the petri dish containing the nutrient agar solution in a zig-zag pattern to ensure that the entire surface of the petri dish was covered.

2. Next, I put the lid back on the petri dish and taped it to ensure the lid would not accidentally fall off. I added the date to each petri dish and placed them in a plastic bag. For the plastic bag, I made sure it was not sealed completely. In order for bacteria to grow, it needs oxygen. If the plastic bag is sealed completely, it could interfere with the bacterial growth process.

3. I used a heater to keep the petri dishes warm and at a constant temperature. Bacteria need a specific temperature to grow and survive (25-35 degrees Celsius).

4. Finally, I placed my petri dishes in a crate to keep them warm and prevent heat from escaping. I put a blanket underneath to help maintain the temperature better.

Microscope Testing

Dry, unwashed rice

Observations

• All of the rice grains have starches that are attached to them, due to not being washed.
• One spot of yellow, which could be a cluster of starch
• Small amounts of dust

Without any washes, you will consume starches, dust, and other dirt particles, which can potentially harm your body. This will also affect the rice you ingest if it is not washed at all.

Zero washes:

 

Observations:

• Tiny piece of hair on one of the grains
• Small specks of dust

This can negatively impact you and your body if consumed frequently over time. These effects could range from minor coughs to nausea. The idea is that consuming unwashed rice often can have fairly significant impacts on you.

One wash:

When I looked at the rice batch that had only been washed once, I noticed that there was still some debris on the rice sample.

Observations:

• Tiny piece of hair on one of the grains
• Small patch of starch 
• Similar to zero washes

The result of this rice sample was fairly similar to the rice sample that had not been washed at all. It had a small amount of impurities, such as starches and a tiny piece of hair.

Two washes:

For the rice sample that has been washed twice, we can analyze that there is also a small noticeable spot of dirt.

Observations:

• Small spot of starch on one of the rice grains
• Slightly cleaner than zero and one wash, though it is similar

From my observations, we can see that this rice sample is slightly cleaner than the first two, though there is a slight contrast.

Three washes:

If we take a closer look at the picture, there is only one thing that can be seen as an impurity.

Observations:

• There is only one speck of dust visible in this photo
• More hygienic than first 3 samples

The rice sample that has been washed three times shows that it is relatively cleaner than the first three rice batches.

Four washes:

As we can see, there are no visible impurities to the naked eye, though the texture is very grainy. Upon closer inspection, there are some imperfections on the rice.

Observations:

• There are some yellow blemishes on some of the rice grains, which can be inferred to be carbohydrates (starches).
• Similar to the first four portions of rice

The reason why this rice batch has more starches than the rice sample washed three times will be explained in the analysis section. Looking at the first five batches of rice, the rice that was washed three and four times is relatively cleaner than the first two batches.

Five washes:

The rice sample that has been washed five times is visibly free from any impurities. We can clearly see that the rice has been thoroughly rinsed, leaving the rice grains clean to the eye.

• Currently the cleanest from the rest of the rice samples

This rice sample, which has been washed five times, shows that washing your rice multiple times can reduce contaminants in the rice that you consume.

Washed until the water was clear:

When washed until the water was clear, this rice batch showed no residues whatsoever. This washing process effectively removes almost all, if not all, of the impurities.

Observations:

• No impurites that can be visible to the naked eye
• Same results as the rice sample that has been washed five times

Washing the rice until the water was clear showed that it was the optimal method, revealing that there were no dust, starches, or other contaminants on the rice.

Petri Dish Testing

Dry, unwashed rice:

Observing the petri dish that was dry and unwashed, it showed many bacterial colonies. This can be assumed to indicate that it had a significant amount of bacteria.

Observations

• Several different species of bacterial colonies
• Dots of bacteria, streaks, and other shapes
• Some colonies are distinct, while others are not
• Has around 450 bacterial colonies

As expected, when observing this petri dish, there were many bacterial colonies. There were many different kinds, varying from Bacillus bacteria to mould.

Zero washes:

 

Looking at these petri dishes, we can see that they have many bacterial colonies, similar to the dry rice sample with no washes. There are also varying types of bacteria on the petri dishes.

Observations

• Different colours of bacterial colonies, indicating there is different kinds of bacteria or mould (white, yellow, and orange.)
• Some colonies of bacteria are easy to count, while others are not due the colonies merging together
• Has around 600 bacterial colonies

These results are similar to the first one, with numerous bacterial colonies of varying colours. This is expected, as both did not have any washes. The key difference is that this petri dish sample had cooked rice, while the other one had dry, uncooked rice.

One wash:

We can identify that the petri dish at the top has some colonies, while the petri dish at the bottom has more.

Observations

• Two different types of colour for the bacteria (white and orange/yellow)
• The petri dish on the bottom has colonies merging together
• These petri dishes samples have averagely less bacteria than the last petri dish samples
• Has around 500 bacterial colonies

Looking at this petri dish sample(s), we can see that it has fewer bacteria than the rice samples that were not washed or cooked. The presence of many bacterial colonies in these petri dishes was anticipated, as they only had one wash.

Two washes:

Considering this rice sample only has one more wash than the third petri dish test, it has a significantly fewer amount of bacterial colonies.

Observations

• Only one colour of bacterial can be seen to the eye (white/yellow)
• On average, it has around 26 bacterial colonies

Examining the petri dish with two washes, it clearly showed that it had a considerably fewer amount of bacteria compared to the rice sample that had been washed once.

Three washes:

Inspecting the rice samples with three washes, it has slightly more bacteria than the petri dish sample with two washes.

Observations

• Two different colours of bacteria (white and yellow)
• An average of 31 colonies in each petri dish
• Has more bacteria than first three petri dishes

Analyzing the petri dishes, they had more bacterial colonies than the petri dish sample with two washes. Some of the bacteria had combined with each other, giving them a slight "fluffy" texture.

Four washes:

At first glance, we can see that these petri dishes are slightly similar to the petri dish with three washes.

Observations

• Two different colours of bacteria (white and yellow)
• Bacteria forming on the edges of the petri dishes
• Some of the bacterial colonies are spots, some have a "fluffy" look, and some have joined together.
• Approximately has 90-100 bacterial colonies

There are bacterial colonies in the middle that can be easily counted. On the edges of the petri dishes, there is bacteria that has combined with each other, making it slightly more difficult to count the bacterial colonies.

Five washes:

These petri dishes have the most amount of bacterial colonies upon first viewing, compared to the other petri dishes.

Observations

• Two different colours of bacteria (white and yellow)
• Almost all of the bacteria have fused together, making it difficult to identify how many bacterial colonies there are
• Has the most bacteria comparing it to the other petri dishes
• Most of the bacteria forming on the edges of the petri dishes
• Approximately around five hundred to one thousand three hundred bacterial colonies.

This rice sample had the most amount of bacteria compared to the other petri dishes. It leads me to wonder why, as it had more washes than most of the rice samples (the reasoning will be stated in the analysis section). When counting the bacterial colonies, I had to approximately count the bacteria by splitting the petri dish into thirty-two sections and counting how many bacteria were in one section. Then, I would multiply the amount of bacteria in that one section by thirty-two.

Washed until the water was clear:

Looking at the petri dish that contained the rice sample washed until the water was clear, it is the cleanest sample out of all the petri dish samples.

Observations

• Only one colour of bacteria (white)
• Has an average of around 20-25 bacterial colonies
• Has the fewest amount of bacterial colonies out of all petri dishes

This petri dish sample had the fewest bacterial colonies, likely due to it being washed until it was completely clean. The method of washing your rice until the water is clear is currently the best way to wash your rice to avoid bacteria from entering your body.

NOTE: When talking about how many bacterial colonies there are, it is an average of how many bacterial colonies were in both/all of the petri dishes. If there were too many colonies to count, an estimation was used by seperating the petri dishes into equal sections. Then, I multiplied the number I counted by how many sections I split it up into.

Microscope Testing:

Dry, unwashed rice: 

Unwashed rice:

Looking closely at the unwashed, cooked rice, it has some impurities, such as dust or a minuscule piece of hair. This was expected, as it is similar to the first sample. One major difference is that this rice sample has been cooked, while the first sample has not. The reason these impurities are present is likely due to the rice being exposed to dust, debris, and other impurities during harvesting, processing, and handling. Since the rice was not washed before it was cooked, any particles that were on the grains remained.

One wash:

When looking at the rice sample that had only one wash, it showed that there was still some debris left. The results were not unexpected, since it had only been washed once. It would not make a drastic difference between the rice that hasn’t been washed and the rice that has been washed once. If you wash something once, it will remove some of the impurities, but still leave some debris behind. This is the case with this rice sample and the rice sample above. Washing it just once does not make a major difference.

Two washes:

If you look at the rice sample that was washed twice, there are only some starches on the rice grains. These results are expected, as washing your rice just a few times would not impact the cleanliness by a significant amount. The outcome of this is quite similar to the first three samples, though it is slightly cleaner.

Three washes:

Slightly surprisingly, the rice sample that had been washed three times only had one speck of dust, which is a major difference. I had expected it to have some impurities left, such as starches or more dust particles. This is likely due to the progression of impurity removal over the course of three washes. The cleaner appearance of the rice after three washes indicates that, with each rinse, more of the surface impurities were removed. Overall, three washes were significantly cleaner than the first three rice samples, which was unexpected.

Four washes:

Five washes:

For the rice sample that was washed five times, there are visibly no impurities. The reason for this can be assumed to be due to it being washed five times, making it free of debris particles or starches. This shows that the more you wash your rice, the fewer impurities you have on it. Washing your rice reduces the amount of contaminants each time you wash it. That's why it is more effective to wash it multiple times rather than just once or less.

Washed until water was clear:

As expected, the rice that was washed until the water was clear had no contaminants on it whatsoever. If we look deeper, it is extremely clean to the eye. The reason this rice sample was the cleanest is the same as for the rice that had five washes. The more you wash rice, the more impurities can be removed. Since this rice sample was washed until the water was clear, it indicates the cleanliness of the rice.

Petri Dish Tesing:

Dry, unwashed rice:

If we look at the petri dish that had the dry and unwashed rice sample, it showed approximately 450 bacterial colonies. This was expected, since it was unwashed, meaning no contaminants could be washed off. There are several different kinds of bacteria, ranging from mould to Bacillus.

Mould: Has a fuzzy texture and can be white or yellow. Since there was no mould on the rice, there are different ways mould could have formed in the petri dish. It could have come from mould in the air. I left some gaps in the petri dishes to allow bacteria to grow more efficiently. Mould spores could have entered through those gaps, allowing mould bacteria to grow in the petri dishes.
Bacillus: Typically has a white, beige, yellow, or grey colour and has rough/sharp edges. The bacteria grown in the petri dishes could possibly be Bacillus cereus.
Since the rice was unwashed, there was a high chance of the rice being contaminated by Bacillus cereus bacteria.

Unwashed rice:

Looking at the petri dishes with the samples of the unwashed rice, they have a similar amount of bacterial colonies to the dry and unwashed rice; they have about 600 bacterial colonies. This was expected, as the rice is identical, with the difference being that this rice sample has been cooked. Using the information above, we can see that these petri dish samples have mould and Bacillus. We can assume that the Bacillus is Bacillus cereus, as rice has a high possibility of containing B. cereus.

One wash:

The petri dish containing the samples of the rice that was washed once had a fairly similar result to the first two petri dishes, with around 500 bacterial colonies. Once again, these results were expected, since it only had one wash. The different kinds of bacteria are mould and Bacillus, which can be identified using the information above.

Two washes:

Surprisingly, the petri dish containing the rice sample with two washes only had 26 bacterial colonies, which is a contrast to the three petri dishes. Looking at the bacteria, we can identify that there is Bacillus bacteria. This was unexpected to me, as in the microscope testing, the rice that was washed twice was not the cleanest out of all the rice samples. There could have been less air inside the petri dish of this rice sample, slowing the growth of the bacteria and resulting in fewer colonies.

Three washes:

Inspecting the petri dish with the rice sample that was washed four times, we can see that there are roughly 31 bacterial colonies. Using the information above, we can determine that there is mould and Bacillus in the petri dish. I had anticipated around 50 bacterial colonies, which is quite similar.

Four washes:

This petri dish contained approximately 90 bacterial colonies, which is a slight contrast to the rice samples that were washed twice and three times. While the difference may seem small, there is still a noticeable gap of around 60 bacterial colonies. This suggests that washing your rice makes a distinguishable difference. We can see that there is mould and Bacillus bacteria.

Five washes:

Washed until water was clear:

Looking at the petri dish containing the rice that was washed until the water was clear, this was the cleanest rice. It had an average of 20 bacterial colonies, showing that washing your rice truly affects its cleanliness. We can only see mould, which likely resulted from air contamination in the petri dish. This petri dish had the fewest bacterial colonies, making it the cleanest petri dish out of all the samples.

In the world, many individuals, including myself, eat rice as part of their daily meals. Some people do not wash their rice, while others wash it until the water runs clear. This experimental project aimed to determine whether different amounts of rice washing could negatively affect you and your body.

The purpose of this project was to find out whether washing rice is truly necessary. I wanted to see what kinds of negative effects it could have on you if it is not washed properly. Based on my experimental results, washing rice does matter, as the rice that was washed until the water ran clear had the cleanest results. There is also a potential risk of consuming Bacillus cereus bacteria, which can negatively affect your body.

Sources of Error

Things I would like to do Differently next time

Aotearoa, H. K. (2023, July 19). Bacillus cereus bacteria in rice and other starchy food: NZ Government. NZ Government. https://www.mpi.govt.nz/food-safety-home/food-poisoning-symptoms-causes/bacillus-cereus-bacteria-rice-starchy-food/#:~:text=Bacillus%20cereus%20is%20a%20bacterium,and%20ways%20to%20avoid%20illness

BC Centre for Disease Control. (N.D). Bacillus Cereus. BC Centre for Disease Control.http://www.bccdc.ca/health-info/diseases-conditions/bacillus-cereus

Canadian Centre for Occupational Health and Safety. (2024, May 10). Pesticides - Health Speaks. Canadian Centre for Occupational Health and Safety. https://www.ccohs.ca/oshanswers/chemicals/pesticides/health_effects.html

DIY bama. (2019, January 5). How to Grow Bacteria. Youtube. https://www.youtube.com/watch?v=JIZ7lj3y4MQ&t=51s

Lin, I. (2024, August 12). How to Rinse Rice. Simply recipes. https://www.simplyrecipes.com/how-to-rinse-rice-5667473

Mantzioris, E. (2023, June 13). Yes, You Should Wash Rice, But Not For The Reason You Think. ScienceAlert. https://www.sciencealert.com/yes-you-should-wash-rice-but-not-for-the-reason-you-think

National Library of Medicine. (2006, August). Screening for and identification of starch-, amylopectin-, and pullulan-degrading activities in bifidobacterial strains. Applied and environmental microbiology. https://pmc.ncbi.nlm.nih.gov/articles/PMC1538741/#:~:text=for%20these%20strains.-,Of%20the%2042%20bifidobacterial%20strains%20tested%2C%2019%20were%20capable%20of,dentium%20strain%2C%201%20B

National Library of Medicine. (2023, January 23). Bacillus Cereus. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK459121/#:~:text=Bacillus%20cereus%20is%20a%20facultatively,nausea%2C%20vomiting%2C%20and%20diarrhea

Nunez, K. (2023, June 16). Yes, You Should Wash Rice Before Cooking It-Here's How. Martha Stewart. https://www.marthastewart.com/8161974/why-wash-rice-before-cooking

Phillips, S. (2021, October 2021). Do You Really Need to Rinse Your Rice? America’s Test Kitchen. https://www.americastestkitchen.com/articles/3946-do-you-really-need-to-rinse-your-rice

Staff, M. M. (2024, June 24). Is Soaking Rice Necessary? Why and How to Soak and Rinse Rice. Million Marker. https://millionmarker.com/blogs/blog/is-it-okay-to-not-soak-rice#:~:text=While%20washing%20or%20soaking%20rice,be%20harmful%20to%20human%20health

Wells, F. (2021, December 13). Should you wash your rice? The scientific method has nothing to do with the texture. Inverse. https://www.inverse.com/science/wash-your-rice

World's Most Eaten Food Discovered: What is our favourite?: AGC Equipment. (2022, December 18). AGC Catering Equipment. https://www.agcequipment.com.au/blog/worlds-most-eaten-food/#:~:text=Rice%20is%20the%20staple%20food,the%20world's%20most%2Deaten%20food

Yam, G. (2022, September 23). Do You Need To Rinse Rice? Epicurious. https://www.epicurious.com/expert-advice/do-you-need-to-rinse-your-rice

 Mr. Thompson (Science Fair coordinator) - Thank you for giving me guidance, helping me get my hands on a tri-fold, allowing me the use of a microscope, and frequently checking in with the science fair participants to ensure our projects are going in the right direction.

Sarah's mom - Thank you for purchasing me a petri dish set to allow me to continue on with my project. I would also like to thank you for helping me with the petri dishes, as it is dangerous for me to boil water without any guidance or supervision.

Sarah's dad - Thank you for purchasing me a tri-fold so that I was able to present my science project, as well as proof-reading my work to check if I had made any grammatical mistakes. Additionally, I would like to acknowlege you for assisting me on adding attachments to the CYSF platform, as I had trouble with it.