Crystallisation & membrane separation

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Questions and Answers

What role do seed crystals play in the crystallisation process?

They initiate the crystallisation process and guide crystal formation. (correct)

They serve as impurities to ensure unique crystal shapes.

They prevent the formation of any crystals.

They change the chemical composition of the solution.

What is the main operation in sugar manufacture that requires uniform crystals?

Evaporation of supersaturated solution. (correct)

Fermentation of sugar cane.

Cooling process for syrup.

Extraction of sucrose from sugar beets.

At what maximum temperature should evaporation be limited to prevent caramelisation of sugar?

85°C (correct)

75°C

55°C

100°C

Which statement is true regarding the crystallisation of salt compared to sugar?

Salt forms crystals more easily than sugar due to temperature independence. Signup and view all the answers

What happens when the correct crystal size is achieved in the sugar crystallisation process?

The desired crystals are separated from the mixture. Signup and view all the answers

What is the primary purpose of crystallisation in food processing?

To separate a solid material from a liquid or produce crystals within a food Signup and view all the answers

What happens during the nucleation phase of crystallisation?

Solute molecules aggregate into clusters that stabilize into nuclei Signup and view all the answers

Which method is NOT commonly used to achieve supersaturation for crystallisation?

Refrigeration Signup and view all the answers

What is the significance of the critical size of clusters during nucleation?

Clusters below this size will not grow and may dissolve Signup and view all the answers

What is one of the primary factors influencing the nature of the resulting crystals in crystallisation?

The temperature and level of supersaturation Signup and view all the answers

What characterizes the cooling method of crystallisation?

It involves gradual cooling of a concentrated solution below saturation temperature Signup and view all the answers

In the context of crystallisation, what is the seeding method used for?

To induce crystallisation when conditions are otherwise challenging Signup and view all the answers

During the process of growth in crystallisation, what occurs?

Stable nuclei grow larger as solute continues to deposit on them Signup and view all the answers

What is the primary function of reverse osmosis in membrane separation processes?

To remove water from other solutes to concentrate fluids Signup and view all the answers

Which membrane filtration method is specifically designed to remove microorganisms from fluid food systems?

Microfiltration Signup and view all the answers

How does ultrafiltration differ in terms of pressure requirements compared to reverse osmosis?

Ultrafiltration requires a low pressure while reverse osmosis requires high pressure. Signup and view all the answers

Which size range of particles does nanofiltration primarily target for separation?

Particles between 1 nm and 100 nm Signup and view all the answers

What type of substances can be separated using microfiltration?

Large proteins and fats Signup and view all the answers

What is a primary application of ultrafiltration in food processing?

To produce high protein powders from cheese whey Signup and view all the answers

What type of materials are typically separated in the reverse osmosis process?

Water and low molecular weight compounds Signup and view all the answers

What is the primary use of nanofiltration in dairy processing?

To partially reduce calcium and other salts while retaining lactose Signup and view all the answers

Study Notes

Crystallisation in Food Processing

Crystallisation is used in food processing to separate or purify substances and to create crystals in food products.
It's important to control crystallisation to get the right amount of crystals with the correct purity, size, and shape.

Crystallisation Process

Crystallisation is a process of making solid crystals from a uniform solution. It involves mass transfer from a liquid solution to a solid crystal.
Crystallisation occurs in two steps: nucleation and crystal growth.
Nucleation is the formation of small clusters of solute molecules in the solvent, which become stable crystals once they reach a critical size. Factors influencing nucleation include temperature and supersaturation.
Crystal growth is the expansion of these nuclei to larger sizes.
Nucleation and crystal growth happen simultaneously while supersaturation exists.
Depending on conditions, either nucleation or growth can be more prominent, affecting the size and shape of crystals.

Methods of Crystallisation: Supersaturation

Supersaturation is a state where a substance holds more solute than it can normally dissolve at a given temperature.
Methods to achieve supersaturation include cooling, evaporation, solvent addition, or adding a precipitant.

Methods of Crystallisation: Cooling Method

A concentrated solution is cooled gradually below its saturation temperature to create supersaturation.
This method typically produces well-defined, small crystals.

Methods of Crystallisation: Seeding Method

To initiate crystallisation, seed crystals are added to the solution (pure crystals obtained from previous batches).
These seed crystals act as nucleation sites, promoting the formation of additional crystals.

Crystallisation Applications: Sugar Production

A major process in sugar manufacture.
Sugar crystals need to be uniform for different products.
Supersaturation is achieved by evaporation (with limits on temperature to avoid caramelisation) and adding seed crystals to the massecuite (syrup with crystals).
Crystals are removed when the desired size is obtained.

Crystallisation Applications: Salt Production

Salt crystalisation isn't dependent on temperature, allowing easier crystal formation compared to sugar.

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Description

This quiz explores the crucial process of crystallisation in food processing. Learn about the two key steps: nucleation and crystal growth, as well as the factors that influence crystal formation. Understanding these concepts is vital for achieving the desired purity and size in food products.