Egg Technology – SS3 Livestock Farming Lesson Note (Second Term)

Egg technology is the study of how eggs are kept fresh (preservation) and how they are turned into other products (processing).

Behavioural objectives

By the end of the lesson, students should be able to:

1. state the two parts of egg technology;
2. explain why eggs spoil;
3. describe the methods of egg preservation;
4. describe the main methods of egg processing;
5. list other products made from eggs;
6. distinguish between a fresh egg and an old egg.

What is egg technology?

Egg technology is the set of methods used to keep eggs fresh and to change them into products that are easy to store and use.

• Egg: a natural container with its own packaging (the shell) and all the nutrients needed to form a chick.
• Quality loss: an egg starts to lose quality as soon as it is laid.

There are two parts of egg technology: preservation and processing.

• Preservation: stopping the egg from going bad or drying out.
• Processing: removing the egg from its shell and turning it into liquid, powder or frozen products for bakeries and factories.

Why do eggs spoil?

Eggs spoil mainly because of water loss, bacteria and heat.

• Evaporation: the shell has thousands of tiny pores, so water escapes over time and the air cell inside the egg grows bigger.
• Bacteria: germs enter through the pores of a cracked or dirty egg and rot the yolk.
• Temperature: in Nigerian heat, the thick part of the egg white turns watery very quickly.

What are the methods of egg preservation?

The main methods of egg preservation are refrigeration, oil coating, water glassing and lime water treatment.

Each method either slows spoilage with cold or seals the shell pores.

Refrigeration

Refrigeration is keeping eggs in a cold store or fridge to slow spoilage.

• Temperature: about 4°C to 7°C.
• Effect: keeps the yolk centred and slows the growth of bacteria.
• Storage tip: keep eggs with the pointed end down, so the air cell stays at the top.

Oil coating

Oil coating is dipping the egg in a thin, tasteless mineral oil to seal the shell.

• Pores: the oil plugs the tiny pores.
• Water: stops water from leaving the egg.
• Air and germs: stops them from entering.
• Advantage: needs no electricity, so it suits farmers without a fridge.

Water glassing

Water glassing is keeping eggs in a solution of sodium silicate.

• Effect: the solution seals the shell completely.
• Duration: keeps eggs fresh for months.
• Advantage: works without electricity.
• Status: an old-fashioned method.

Lime water treatment

Lime water treatment is keeping eggs in a solution of calcium hydroxide (slaked lime).

• Effect: the solution seals the pores and keeps out germs.
• Advantage: cheap, and needs no electricity.

How do the preservation methods compare?

How are eggs processed?

Egg processing is breaking eggs out of their shells in large numbers and turning them into liquid, powder or frozen products.

A bakery does not want to crack thousands of eggs by hand, so factories do it by machine.

What are the steps in egg processing?

1. Wash and sort the eggs.
2. Check each egg for cracks and bad eggs (candling, using a bright light behind the egg).
3. Break the eggs by machine.
4. Filter out bits of shell.
5. Pasteurise the liquid egg.
6. Pack it as liquid, dry it into powder, or freeze it.

Liquid eggs

Liquid eggs are eggs cracked by machine, filtered and packed in cartons.

• Pasteurisation: the liquid is heated briefly to kill germs such as Salmonella without cooking the egg.

Egg powder (drying)

Egg powder is made by spraying liquid egg into a hot chamber, where the water evaporates and leaves a fine yellow powder.

• No fridge: egg powder does not need cold storage.
• Shelf life: it keeps for a long time.
• Transport: it is light and easy to carry to remote areas.

Frozen eggs

Frozen eggs are liquid eggs frozen for storage.

• Salt or sugar: a little is added before freezing to stop the egg from becoming rubbery.

What other products come from eggs?

Other egg products include mayonnaise, eggshell meal and lysozyme.

• Mayonnaise: egg acts as an emulsifier that holds oil and vinegar together.
• Eggshell meal: dried, crushed shells are a source of calcium for animal feed and garden fertiliser.
• Lysozyme: a protein in egg white that kills bacteria and is used in medicine.

How does a fresh egg differ from an old egg?

A fresh egg is one laid recently, with little water lost and firm contents.

An old (stale) egg has lost water through the pores, so its air cell is large and its contents are thin.

What class discussion and practical activities can be done?

1. Float test: put a fresh egg and an old egg in a bowl of water. Ask students to explain the difference using evaporation.
2. Home experiment: if you have no fridge, how can you use vegetable oil to make eggs last longer?
3. Critical thinking: why would a biscuit factory prefer egg powder to crates of fresh eggs? Think about storage, transport and shells falling into the dough.

Evaluation

1. State the two parts of egg technology.
2. Name three causes of egg spoilage.
3. Explain how oil coating preserves eggs.
4. Give two reasons why egg powder is useful to factories and remote areas.
5. Describe the float test and say what it shows about an egg.

Assignment

Write four differences between a fresh egg and an old egg, then name two other egg products and state one use of each.