Spices vs. Microbes

Casia switched from ancient civilizations to early American history this past spring. As a lead in, we studied various indigenous people of the Western hemisphere and early exploration and conquest by Europeans. To go along with this line of study, I found a couple of interesting articles on the big why behind the drive to explore. 

Since the acquisition of spices was such a major impetus, I found this interesting article on the subject and shared it with Casia. Spices: How the Search for Flavors Influenced Our World, written by Paul Freedman, examines the historical impact of the spice trade. In another article, What's So Hot about Spices?, by Gail Jarrow and Paul Sherman, the authors discuss the use of spices as food preservatives. This led me to the idea to combine some science and history and after a little Googling, I found this experiment:  Food Preservation.

I prepared some broth ahead of time. Casia then selected five spices: salt, pepper, sugar, cinnamon and allspice. She labeled the containers with the spice names, plus one for a control and the other labeled boiled.

She then added one cup of broth to each container followed by one teaspoon of the corresponding spice. No spices were added to the control or boiled containers.

 Casia stirred.

And then they were left without the lids on overnight in the kitchen. The next day, Casia covered all the containers except for the boiled. The boiled sample was first boiled and then left to cool for a few minutes and then covered. All containers were then left to sit for three days.

I asked Casia at the start of this lab to guess which containers would have the most microbe growth. This is what she predicted:

Most growth to least:  sugar, control, cinnamon, allspice, pepper, boiled and salt.

Now that the containers had been sitting for a few days, it was time to open them up. Casia did a great job with her lab write-up including a chart she made for her observations. She inspected each sample for smell, then with the unaided eye and then under the microscope. 

We decided that a good way to determine the amount of microbe growth would be to randomly select four areas under the microscope and then she would estimate what percent of the area that she saw under the microscope was covered in microbes. Then she averaged the four samples per container to come up with an overall estimate of microbe growth for that solution.

Casia got a lot of practice making her own slides for this lab. After six smelly containers (Casia claims the allspice solution still smelled 'yummy'), seven slides, 28 views under the microscope, and ten minutes to calculate and make a snazzy chart, Casia was ready to announce the winners in the spices vs. microbes.

Most growth to least:  sugar, control, cinnamon, pepper, allspice, boiled and salt.

Here are her results:

Spices	Salt	Boiled	All Spice	Pepper	Cinnamon	Control	Sugar
#1	15%	20%	10%	60%	40%	70%	70%
#2	5%	40%	50%	30%	90%	65%	80%
#3	30%	32%	5%	70%	2%	80%	60%
#4	10%	25%	90%	20%	50%	40%	70%
Average	15%	29%	39%	45%	45%	64%	70%

Casia's guess was really close! Her allspice and pepper were reversed. We both agreed that we we wouldn't want to consume any of the samples, as even the salt smelled foul. And with only four random samples per container, some with a range of more than 80%, she probably should have taken more sample views. But she was given only a couple of hours to complete this section of the lab. It also might have been interesting to see what would have happened had she combined multiple spices in a given sample. 

Overall, this lab was very easy to do (though a little smelly), used supplies I already had on hand and rated an awesome from Casia.