Group 063-001: Coffee Extraction Process

During week eight of lab, our group began testing with our newly assembled device. By varying the brew time between one and six minutes, we measured the pH, conductivity, and mass of the brew to find an ideal brew time. Our data is recorded under the second brew within the brew notes tab.  Throughout testing, the issue of the thin, paper filter breaking from the pressure difference in the final vacuum; Ethan suggested that we supplement the paper filter with  a metal aeropress filter. This adjustment resolved the problem; however, as a result, we had modified one of the constants in the initial runs of our data. These trials will be redo in week nine of lab for consistency among all brew times. Pictured: Alex measures out the grounds, while Ethan prepares the station for our brew trials (left). Anna and Saeed watch as Ethan monitors the brewing coffee (above right). Ben measures and estimates the pH of a sample of the brew, while Angie takes the conductivity of the s...

In our week seven lab, our group began assembling our brewer with the new, heat and pressure safe materials. Ethan began fitting the vinyl tubing around the funnel for a secure fit; Ben drilled a hole through the rubber stopper for a secure transport of the water and coffee. Once the brewer was assembled, we began preliminary testing. From our first test, we used hot water for our water source. This posed as a problem given the hot plate was not set to a temperature that was significantly higher than the boiling point of water. The water cooled, and the pressure did not build up. Additionally, the seal between the tubing and the rubber stopping has slight leakage. In a second test, hot water was placed on a hot plate that was set to 280 degrees Celsius to account for heat transfer through the Pyrex flask. Ben secured the seal on the rubber stopper with hot glue (other methods of securing the stopper will be tested later).This brew served as our first functional initial brew, and Note...

Because of design setbacks from week five, material delivery delayed continued work on the mechanical design of our brewer. During week six, Angie, Alex, and Anna worked on the initial draft of the final report, while Ben and Ethan worked to find heat ratings for the new Pyrex vessels. Our group felt worried while reading conflicting specs sheets; however, a brief phone call brought clarity and relief to our group: the Pyrex would safely withstand the temperature of the hot plate. Additionally, Ethan drilled a hole within the rubber cork for the Erlenmeyer flask for a secure fit for the tubing. Now, our group will order tubing that will withstand the temperature and pressure of hot water. For Week 7, our group will begin to assemble the improved and safer design of the brewing device and possibly begin testing.

During week five of lab, our group began building our prototype. We started with the essential components to our design: two storage vessels, glass tubing, and a vertical wooden base. Our first step was to scale our components, and gaining access to resources within the lab posed as a problem. Ethan began filing the glass tubing to alter the height of the overall design. Ben and Anna measured the size of holes needed to be drilled within the cork and bottle cap, which would allow tube access while maintaining the pressure (and eventual vacuum). Alex and Angie worked on fitting the tubes and overall design together. Overall, we decided that we still needed a plastic funnel and metal clamps to easily attach/ remove the bottles to the wooden base. Saeed suggested that we changed our vessels for safety precautions. We were lent two Erlenmeyer flasks, and we now are considering a horizontal display, which would involve a change in tubing. Pictured: Angie and Alex display the initial ve...

During week four, we studied the process of mass transfer and flux during the brewing process. One of the goals we have set forth for our design is to gain maximum extraction while maintaining a low acidity brew. While only 30% of coffee is soluble (the other 70% is cellulose which is not soluble), a good-tasting cup of coffee holds 19%-21% of dissolved solids. In order to achieve this, the variable we decided to manipulate was extraction time, given that is easily controlled in the siphon brewer. Our two testing times were one minute and ten minutes, in which calculated the conductivity at each minute. To relate conductivity to the amount of total dissolved solids, we created a calibration curve using instant coffee, coffee comprised solely of dissolved solids. By matching the amount of instant coffee to conductivity values, we were able to match our found conductivity values to the curve to find the corresponding concentration. Then, using the mass of the brew at each time, we fou...

During our third week of lab, we began to explore the chemical properties of coffee through experimentation. We experimented with the pH of dark and light roast beans. Within the first part of the experiment, we measured the pH over a 50-minute time period and recorded our sensory evaluation at the start, midpoint, and conclusion of the period. We found the rate at which the concentration of hydronium ions increases (the rate at which the pH is lowered). For the second part of the lab, we compared the pH of light roast (5) to dark roast (6), finding that the light roast was more acidic than the dark roast. By performing this lab, we were able to establish a relationship of pH to time and relate product quality to pH. Additionally, we established our goal of achieving low acidity.