Week 3: Feeling the Burn

Lecture

In lecture this week, we began to talk about analyzing coffee extraction through different experimental methods. We started to go more in depth about what extraction processes are and how they work, specifically in coffee. We learned about how coffee beans are porous and how that enables water to extract the soluble compounds through diffusion, making coffee.

We then started to talk about how to design extraction experiments and what to consider. The main aspects that we will focus on in this course are temperature, particle size, particle size distribution, solid to liquid ratio, and extraction type. For this week, our main focus will be temperature. Some details to focus on while doing these experiments are what variables will be kept constant, what analytical data will be observed, how many runs will be performed, how many data points will be obtained from each run, and most importantly, for this week, what temperatures will be tested.

Note: This week, we also completed our project design proposal, which basically summarizes what we want to accomplish, and how we will do just that in the following weeks.

Procedure

Of course, if you’re performing an experiment, you have to create a procedure to do so, and that’s exactly what we did. We had to figure out how we would run the experiment, how many times we would run it, what data we would collect, any safety precautions to remember, and again, the temperatures that would be tested. We decided to run a flow extraction once at three different temperatures, getting around eight points from each run. We had to remember to be careful mainly about mechanical equipment and heat from boiling water. As for the temperatures we chose, we chose room temperature as sort of a control group, around 93°C to be close to the boiling point of water, and around 68°C as a midpoint between the two. We hypothesized that 93°C would get the optimal coffee extraction because generally as heat increases, solubility also increases. Anyway, here is the experimental procedure we came up with:

~ Equipment setup

1. Coffee burr grinder

2. Coffee beans

3. Coffee filter cone

4. Coffee filter paper

5. Water

6. Measuring cup

7. Measuring probe

8. Kitchen scale

9. Kettle

10. Drip scale

~ Steps

1. Boil at least 4 cups of tap water to get rid of the impurities in the tap water

2. Let the boiled water cool down to room temperature

3. While water is cooling, grind 30 grams of coffee beans to 0.5 mm size and then measure out 20 grams of grinded coffee beans

4. Assemble the flow extractor by placing a coffee cone on top of a container on top of the drip scale

5. Place the filter paper into the cone

6. Using tap water, wet the sides of the filter paper onto the cone

7. Put the 20 grams of ground coffee on top of the filter paper.

8. Heat one cup of the cooled water to 93 C

9. Start pouring the cup of water over the coffee ground inside the coffee cone

10. Let the coffee filter drop for exactly 2 minutes (start the timer as soon as water gets poured in)

11. Remove and dispose the filter paper and the remaining coffee grounds

12. Measure the conductivity of the coffee three times after the coffee is done filtering

13. Clean the containers and probe for next trial.

14. Repeat steps 1-13 twice more but heat up the temperature of the water to different temperatures at step #8.

15. Clean the containers and probes.

Essentially, the experiment will look like this:

Lab

Now that we’ve figured out what we want and how we will get it, it’s time to run the experiment. We first ran this experiment with an extraction at room temperature (23°C). We first had to measure out the coffee to be 20 grams. The measuring cup was 418 grams. Then we had to grind the coffee beans while conserving the mass at 20 grams. Then, it was finally time to begin the filtration.

The end result:

Then came data analysis (it says 4276):

Now for rounds two and three.

For these runs, we had to increase the temperature to 68°C and 93°C, respectively.

The higher the temperature, the harder it was to get it completely accurate.

Anyway, once we got all three runs done and the data recorded, it was time to analyze it. The concentration was obtained from the conductivity by using the calibration curves we made last week.

Here is the data acquired:

Then we calculated the total extraction of coffee at each temperature.

Conclusion

From this experiment and the data we collected, we determined that the optimal temperature for coffee extraction, and theoretically other solid liquid extractions, is 93°C. This is because while for some members, the graph peaked the highest at 68°C, the extraction yielded the most coffee at 93°C. Now, we’re one step closer to perfecting our process!!!