3.5
3.5.1
Freeze dried coffee
Introduction
In this section we continue to investigate the phenomena of phase change. The concept of solids melting to a liquid and then vapourising to a gas is easy to understand. But is it possible to skip at step?
In this section we shall see how that might happen, and why it might be useful to us.
Terms
Be able toBy the end of this section you should be familiar with terms such as:
Phase transition
Sublimation
Use a phase diagram to illustrate the process of freeze drying
3.5.3
Freeze dried coffee
Pause for thought
Freeze dried coffee process in a vacuum
air extracted
water extracted
Instant coffee
Ground coffee
In the video we learnt about the process of freeze drying and why this is so valuable today for preserving food stuffs.
What do you think the advantages of freeze drying are?
The name gives some clues, but why do think freezing might help dry?
Do you think there are any constraints on the temperature or pressure?
3.5.4
Freeze dried coffee
Screencast
Outline
In this unit we will continue to investigate the phenomena of phase change. The concept of a solid melting to a liquid and then evaporating to become a gas or vapour is easy to understand, but is it possible to skip a step?
In this unit we will see how that might happen and why it might be useful to us
3.5.5
Freeze dried coffee
Review Questions
-
Referring to the material presented in this section, can you answer the following questions -
What is referred to as the “Critical Point” on a phase diagram?
-
Referring to the material presented in this section, can you answer the following questions -
What is referred to as the “Triple Point” on a phase diagram?
-
Referring to the material presented in this section, can you answer the following questions -
What is the difference between a “Vapour” and a “Gas”?
-
Referring to the material presented in this section, can you answer the following questions -
What is referred to by the term “sublimation”?
-
Referring to the material presented in this section, can you answer the following questions -
What actually is “dry ice”?
-
Referring to the material presented in this section, can you answer the following questions -
Why does “dry ice” apparently give off a mist like vapour?
-
Referring to the material presented in this section, can you answer the following questions -
What is the process of freeze drying?
