Senior Lab - Week 1

Equipment and Materials

Equipment

• Popcorn popper/roaster
• Coffee grinder
• Electric kettle
• Brush
• Timer
• Mesh colander
• Metal bowl
• Digital balance (± 0.1 g)
• Graduated cylinder (100 mL)
• Drip brewer
• Filter paper
• Beakers (250 mL, 500 mL, × 3)
• Valve storage bags (3 per team)

Materials

• Green coffee beans (≥250 g per group)
• Water (≥ 1.5 L per group)

Background

Congrats! You just got a job at Williamsburg’s most obsessively particular micro-roastery as their newest coffee developer. You survived the five round interview and now it’s time to earn your apron.

Your first client is a boutique hotel in the West Village, who wants a ready-to-serve pour over brew. They are asking you to design a roast-to-brew process that reliably produces 600 g of brewed coffee per batch, hitting a Total Dissolved Solids (TDS) of 1.2–1.4% and a percent extraction (PE) of 18–22%.

Over the next 3 weeks, you’ll need to get data for selecting an appropriate roast profile, grind size, water temperature, brew ratio, and contact time that together hit these targets.

Infographic…..

Roasting

Roasting begins with green coffee beans as the sole input. As the beans are heated, three streams exit the system:

1. Roasted coffee beans
   
2. Chaff, the thin outer skins that flake off during roasting
   
3. Escaping gases, including water vapor, carbon dioxide, and other volatile organic compounds (VOCs)

Brewing

Similarly, during brewing, the input water exits the system as brewed coffee, moist spent grounds, and evaporated steam. For simplicity, we will neglect the mass lost to evaporation and ignore dissolved coffee solids in the brewed coffee.

Coffee grounds absorb a finite amount of water. To quantify the amount of water retained in the spent grounds, we define the absorption ratio:

\[ R_{\text{abs}} = \frac{\text{mass of water absorbed into coffee grounds}} {\text{initial mass of dry coffee grounds}} \]

By performing a mass balance, the amount of drinkable coffee produced can be determined if the mass of input water, the mass of dry grounds, and the absorption ratio are known. This week, you’ll determine the absorption ratio empirically by varying the amount of coffee grounds while holding the input water mass constant.

Part 1: Roasting + Brewing

1a: Roasting

1. Measure the green coffee beans.
   Weigh and see the volume of approximately 250 g of green coffee beans and record the volume they occupy in a graduated cylinder. Roast your full green bean supply in batches of ~80 g. All batches must be roasted to the same level that you select. This stock will supply all brews on Weeks 1, 2, and 3.

   

   Green coffee beans

2. Roast the coffee beans.
   For a light roast, stop shortly after first crack. For a dark roast, continue 2–3 minutes past first crack. Record roast time and observe color and aroma changes at first crack and end of roast.

   

   Roasting

3. Weigh the chaff and roasted beans.
   Allow the beans to cool for a minimum of 5 minutes, then transfer them to a mesh colander. Collect the chaff that falls through the mesh and brush out any remaining chaff from inside the roaster. Weigh the chaff and roasted beans separately. Finally, transfer the roasted beans to a graduated cylinder and record the new volume. Calculate the percent volume change.

   

   Chaff

4. Combine all roasted batches. Divide into three equal portions and seal each in a valve bag. Label with roast level, date, and team name. Store at room temperature away from direct light.

1b: Absorption Ratio

All three brews use the same mass of water (~300 g) at 94 °C. Only the mass of grounds changes: approximately 30 g, 20 g, and 10 g.

1. Grind the roasted coffee beans.
   Grind all roasted beans to a medium grind.
2. Weigh the parts of the pour-over carafe.
   Weigh the pour-over carafe (empty, dry) and the filter paper + dripper separately. Record both.

3. Prepare a brew.
   Weigh the target mass of grounds into the filter. Weigh the target mass of water into the kettle; heat to 94 °C. To brew, pour all water over the grounds in a slow, circular motion. When dripping stops, record the total elapsed contact time.

Water

4. Measure the coffee brewed.
   Immediately weigh: (a) the carafe containing brewed coffee; (b) the dripper + filter + moist spent grounds. Calculate the mass of the brewed coffee, spent grounds, and water in the brew.

5. Repeat.
   Repeat Step 6 for two additional brews using the same mass of water, but with 20 g and then 10 g of coffee grounds. Record the absorption ratio you found, and the \(R^2\) value.

1c: Process Flow Diagram

Using Brew 1 data, construct a fully labeled PFD for the complete roast-to-brew process. Start with green coffee beans and water as inputs; end with brewed coffee as the product.