Kids love to eat, and they obviously love food, so it stands to reason that they love labs in which they can eat what they produce. After all, any science teacher can tell you that kids ask if they can eat lab materials ALL THE TIME. It doesn’t matter if it’s sugar or sulfuric acid, as long as it looks edible, the questions will fly. That is why it’s important to include food labs in the class repertoire and finally be able to answer “yes” when a student asks if they can eat a lab material.
In response to the fact that we had been studying bacteria and how it grows, a student asked if we could make yogurt. Given that bacteria factor heavily into the yogurt production process, I realized this would be a great way to continue our exploration. We already saw the effects of bad bacteria, so why not focus on the useful parts of this gigantic kingdom of microscope creatures? After a very thorough cleaning of the lab and incubator using UV lights to ensure sanitary conditions, we began our deep dive into food production.
We started off simply by using yogurt (greek or regular) as a base to grow in milk (whole, 1%, 2%, chocolate). The students realized quickly that the bacteria in the yogurt is going to reproduce at a pretty rapid rate, consuming the milk as it goes and doing whatever it does to produce the stuff that they know well and eat on a regular basis. One important experimental note I told them was that they had to boil their clean, newly purchased, “food safe,” beakers prior to each bacterial growth, as well as heating the milk up to 85C-90C. I didn’t expressly tell them it is to kill off bad bacteria; they looked that up for the post lab questions. Also, some students made the mistake of putting their yogurt in immediately after heating and were disappointed to discover that no growth had occurred within the yogurt. They quickly realized that they needed to cool the milk down so as to not kill the newly added bacteria, which was a valuable part of the scientific process.
For the follow up experiments, we looked at using a variety of different yogurt starters, each with slightly different bacterial compositions. The students researched the different strains to determine what the packets had it common and hypothesized the exact amounts of bacteria in each one. They performed a number of growth cycles looking at the effect of these starters and how they affected taste, consistency, and speed of growth of the yogurt, perfecting their protocols at each step.
I made sure not to give them too much of the story behind why yogurt is formed and allowed them to uncover the science behind it after the experiments. When we concluded the yogurt cycles, the students had a lot of questions as to what they had just done. I guided them toward a list of basic questions, which included, “What about the bacteria makes milk thicken when incubated?” The students uncovered pretty quickly that the bacteria eat the milk sugar (aka lactose) for food and produce lactic acid as a waste product, which changes the pH of the milk, degrading some of the proteins, and thus thickening the overall product. This is similar to the effect of acid on enzymes and goes along with the general acid-base studies we did earlier in the year, so we were able to use this as a summative exercise on important concepts we’ve covered throughout the school year. While I could say that this was my plan all along, I will admit it ended up being a very happy accident.
Next, we explored the production of cheese, which was also suggested by a student. We designed two basic types of cheeses: acid and rennet produced. In addition, we used a whole new set of bacterial starters designed for cheese. We started with acid-formed cheeses that use the same coagulation principles as yogurt to curdle milk, but under high heat the curds (mostly fats and protein) split from the whey (mostly sugar and some protein), which can then be strained to produce anything from farmer’s cheese to mozzarella. Rennet is an enzyme solution that breaks down lipid and protein structures in the milk resulting in many common aged cheeses, like cheddar, and ties together some concepts from our enzyme unit earlier in the year.
We spent about 3 weeks exploring the production of cheese and looking at it from various scientific angles to see if the students could get a smoother texture, stretchier mozzarella, and all around tastier cheese by modulating the flavors with salt and other spices. Since most of the students were using recipes they found online, they also got practice in following directions and altering steps when time was a problem to see if that changed the overall structure of the cheese. By the end, many students were creating their protocols based on prior research, which really is the heart of proper experimental design.
The principles used to make the two foods are similar, and the students really enjoyed the exploration and the act of producing something at the end that was edible. They also received important knowledge as to what is in their food and how science is used to create the things they like. I sampled most of the students’ work and suffice it to say that many of the creations were quite tasty. So not only can food labs be a treat for kids, but instructors as well, and since they all followed proper safety protocols, not one illness resulted. Overall, this was a great summative exercise to tie together many of the previous concepts we have studied over the past year.