What is the best way to wash berries and remove germs?
For these experiments, I wanted to determine if rinsing berries in water was sufficient to remove germs. Rinsing in water does a pretty good job, but it isn't going to remove every germ. I still rinse and eat a LOT of berries, though. Yum!
FRESH RASPBERRIES
For this experiment, I wanted to determine if simply rinsing fresh raspberries in tap water was good enough to remove most of the germs. First I took a dirty raspberry right out of the box and rubbed it all over one half of an agar plate. I used a sterile swab to hold the raspberry. I got a second dirty raspberry and rubbed the same half of the agar plate. So, there were 2 dirty raspberries rubbed on that half of the plate.
Next I took a raspberry and rinsed it really well under tap water. I let the water run on it for about 20 seconds.
Then I used a sterile swab to rub this clean raspberry on the other half of the agar plate.
I repeated this with one more clean raspberry. So, two clean raspberries were rubbed on that half of the agar plate. The agar plate was then placed in my warm (about 95 degrees F) incubator for 15 hours.
After 15 hours, I examined the plate for colonies of bacteria. I am quite impressed at how well just rinsing with water removed the germs from the raspberries!
I repeated the same experiment with the raspberries but this time I rinsed several raspberries in a strainer together. I mixed them gently with my hand while the water was running so each raspberry got rinsed. I rinsed them for 2 minutes. Then I rubbed 2 dirty raspberries and 2 rinsed raspberries onto an agar plate and incubated them overnight.
As you can see, giving raspberries a good rinse with water seems to be very effective at removing bacteria.
FRESH BLUEBERRIES
For this experiment, I wanted to determine if simply rinsing fresh blueberries in tap water would be enough to remove most of the bacteria. I used a sterile swab to roll 2 dirty blueberries around on one half of an agar plate.
Then I rinsed the blueberries under cool tap water for 2 minutes. I used my hand to gently mix the blueberries so each one got rinsed.
I used another sterile swab to roll 2 clean blueberries around on the other half of the agar plate. I incubated the plates overnight. As you can see, just rinsing with water did a good job removing the bacteria. There is a little bacteria at the bottom on the clean side. However, that was caused when one of the dirty blueberries that I was rolling on the other side accidentally rolled out of bounds. It seems that just giving blueberries and raspberries a good rinse with tap water does a good job removing germs.
FRESH STRAWBERRIES
Next, I wanted to determine if rinsing strawberries in tap water was enough to get them clean. First I rubbed 2 unwashed strawberries (one at a time) onto an agar plate. I used a sterile swab to push them around.
Then I rinsed 2 different strawberries (one at a time) under running tap water for 1 minute. I used my other hand to gently rub the outside of the strawberry.
I rubbed the 2 clean strawberries on another agar plate and pushed them around with a sterile swab. (I took a photo of that but it was blurry.) Then I incubated the plates overnight in my warm incubator.
As you can see, rinsing with water for 1 minute is a great way to clean strawberries! I realize that most of us don't want to spend 1 full minute cleaning each strawberry.
I repeated this experiment with strawberries a different day. This time I only rinsed and rubbed each strawberry for 15 seconds under WARM running water. As you can see, the 2 strawberries got almost perfectly clean.
Negative Control
For all of my produce washing experiments, I do this negative control. I wanted to make absolutely certain that my tap water and clean gloves were not contributing bacteria to my experiments. So, I put on a clean pair of gloves, got them wet under the tap water, and rubbed them on a clean agar plate.
I incubated the plate overnight and was pleased that there was no bacterial growth at all the next day.
