Engineering aspects of food technology Flashcards
What do tea leaves contain a lot of?
phenolic components (polyphenols)
What does rolling tea cause?
This will open the cells and vacuoles that have the phenolic components and expose them to oxygen and the enzyme polyphenol oxidase. This oxidation makes the infusion more yellowish.
What doe the berries of Coffae tree s contain?
a lot of caffeine and phenolic compounds
What happens when coffee beans are heated in an environment that contains little oxygen?
Many carbohydrates degrade and carbonize (fall apart into carbon, CO2, water and other molecules). A lot of gasses are produced, which expands the beans to a factor two and makes the beans very porous. Also, almost all the phenolics are lost.
How does the roasting process go?
At first temperature not too high: endothermic process. After some time temperature is increased and process becomes exothermic. From this point on the roaster has to actively cool the beans.
What is the Brownian motion?
The fact that diffusion is caused by random thermal motion of molecules, due to the incessant collisions between molecules due to their temperature.
A reduction in size of 2 will give a reduction in volume/mass by a factor of …
8 so V=R^3
If a particle is twice as small, it will have a surface area … times as small.
4 so A=R^2
What is the steepness of the concentration?
twice as large –> particle twice as small = change in concentration spread over a distance twice as small
What is the overall scaling relation for the brewing time of coffee?
t ∝ R^2
What is the scaling relation that gives the time for the water to move through the bed of coffee grounds?
t ∝ R^-2
How is it that cold-brewed coffee seems the have fewer undissociated acids?
Some of the organic acids in coffee are extracted less at lower temperatures. This is because acids in their undissociated form are more hydrophobic and will dissolve less at lower temperatures.
Why doe we not use a drip system for making tea?
tea, even when grinder, requires a longer time for extraction. And since different molecules diffuse at different rates, forcing the tea to be extracted faster would not result in good quality tea.
