Lab 1

Equipment and Materials

Equipment

• French press
• Coffee grinder
• Digital balance
• 500 mL volumetric flask or beaker
• Electric kettle, or hot plate and thermocouple
• Stirring rod or spoon
• Timer
• Heat-resistant gloves or mitts

Materials

• Roasted coffee beans (≥ 30 g per group)
• Water (≥ 500 mL per group)

Background

One goal of this lab is to create a process flow diagram (PFD) for making coffee. A process flow diagram is like a map of a process. It shows how materials move through different steps and pieces of equipment. In chemical engineering, PFDs usually show only the main steps and equipment. Small details like pipes and valves are often left out. In large industrial systems, like a petroleum refinery, these diagrams can become very complex.

Process Flow Diagram: Doing your Laundry!

Luckily, we will start simple. Above is an example of a process flow diagram for doing laundry. Notice that mass must be conserved around each step: what goes into a step must come out in some form. When you create your own process flow diagram for a coffee brewer, think carefully about what goes in and out of each step. Every input and output should be shown with its own arrow.

Part 1: Brewing the Coffee

1. Measure the coffee beans.
   Weigh approximately 30 g of roasted coffee beans.

2. Grind the coffee.
   Place the beans in a grinder and grind them to a medium–coarse size, similar to coarse salt or breadcrumbs. This grind size is appropriate for a French press.

3. Prepare the French press.
   Weigh the empty French press with the lid and record the mass.

   Mass of empty French press: ____________________ g

4. Add the coffee grounds.
   Weigh the ground coffee and transfer it into the French press vessel.

   Mass of coffee grounds, \(m_g\): ____________________ g

5. Measure and heat the water.
   Weigh the empty beaker, then measure 500 mL of water in a beaker and weigh it again. Heat the water to 88 C.

   Mass of water added, \(m_w\): ____________________ g

6. Add water to the French press.
   Carefully pour the hot water into the French press containing the grounds.

   

7. Steep the coffee.
   Allow the mixture to steep for 10 minutes. After 1 minute, gently stir to ensure all grounds are wet.

   

8. Plunge the French press.
   Place the lid and plunger on the French press and press the plunger slowly and steadily to the bottom.

   

9. Collect the brewed coffee.
   Pour all brewed coffee into the beaker and weigh it.

   Mass of brewed coffee, \(m_c\): ____________________ g

   

10. Weigh the spent grounds.
    Weigh the French press containing the moist spent grounds.

    Mass of spent grounds, \(m_{\rm sg}\): ____________________ g

Part 2: Analysis

Brew Ratio

An important parameter for brewing is the brew ratio, defined as:

\[ R_{\rm brew} = \frac{m_w}{m_g} \]

This number usually ranges from 14 to 19. In later experiments, we will explore how changes in the brew ratio affect the taste. The higher the brew ratio, the weaker the coffee.

Calculate your brew ratio from Part 1:

Mass of water, \(m_w\): ____________________ g
Mass of dry coffee grounds, \(m_g\): ____________________ g

\[ R_{\text{brew}} = \_\_\_\_\_\_\_\_ \]

Process Flow Diagram

Using software or paper, sketch a process flow diagram (PFD) for brewing coffee.

• Start with roasted coffee beans and end with a final beaker of brewed coffee.

• Represent each step with a labeled rectangle (for example: grinder, French press).

• Draw arrows for all material streams entering and leaving each step, including any waste streams.

• Label each stream with the corresponding masses you measured in Part 1.