Question

In Coffee, the Roasting process causes the beans to expand and lose weight mainly due to the loss of ______.

• A. caffeine
• B. moisture and $\text{CO}_2$
• C. lipids
• D. proteins

Hint:

Superheated steam and generated $\text{CO}_2$ gas build up pressure inside the tight cell walls of coffee beans. This pressure forces the bean to puff up and double in volume, while the steam release causes weight loss.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the primary volatile compounds lost during the high-temperature roasting of green coffee beans, which causes them to expand physically while losing overall mass.

Step 2: Detailed Explanation:

• Roasting Changes: Roasting is a thermal process (typically $180^\circ\text{C} - 240^\circ\text{C}$) that transforms green coffee beans into aromatic, brittle brown beans. This process causes a mass loss of $12\% - 20\%$ alongside volume expansion.

• Moisture Evaporation: Green coffee beans contain about $10\% - 12\%$ free and bound moisture. During the early stages of roasting, this water is heated, evaporates, and is released as steam, accounting for the largest portion of the weight loss.

• Generation of Carbon Dioxide ($\text{CO}_2$): As roasting temperatures rise, pyrolysis of sugars and carbohydrates occurs, releasing large volumes of carbon dioxide ($\text{CO}_2$) gas. This gas pressure builds up inside the bean's cellular structure, forcing the walls of the bean to stretch and expand (causing the "first crack" sound), which increases bean volume.

• Why Other Options are Incorrect: Caffeine is highly stable and sublimation is minimal during roasting. Lipids and proteins undergo chemical changes (melting and Maillard reactions) but remain within the bean matrix, contributing very little to the overall weight loss.

Step 3: Final Answer:
The loss of moisture and generated carbon dioxide gas is the primary cause of bean weight loss and physical expansion during coffee roasting, corresponding to option (B).