Biotechnology

Bread.

• Yeast added to dough.
• Yeast ferments SUGAR → CO₂ + ethanol.
• CO₂ TRAPPED in sticky dough → bubbles → DOUGH RISES.
• Baking kills yeast and EVAPORATES ethanol.
• Result: light, fluffy bread.

Beer + wine + spirits (brewing).

• Yeast added to sugar source: barley malt (beer) or grape juice (wine).
• Sealed tank → low O₂ → ANAEROBIC fermentation.
• Sugars → ETHANOL + CO₂.
• Ethanol stays in liquid → alcoholic drink.
• CO₂ may be retained for fizz (beer, sparkling wine) or released.

Why it stops:

• When ethanol reaches ~12-15%, it kills the yeast.
• That's the natural ceiling for fermented drinks.
• Spirits (vodka, whisky) are made by DISTILLING fermented liquid → much higher alcohol %.

Worked qualitative. Why does fresh dough taste a little ALCOHOLIC if you let it rise too long?

• Yeast keeps producing CO₂ AND ethanol.
• The longer the rise, the more ethanol accumulates.
• Some doesn't fully evaporate during baking.
• Slight alcoholic note in some breads (sourdough).
• Why kids' books cute idea of yeast 'eating sugar' is essentially correct.

Cambridge tip. Always state ANAEROBIC respiration for brewing, and mention BOTH products (ethanol AND CO₂).

The problem. Some people can't digest LACTOSE (milk sugar) — they lack lactase. Symptoms: bloating, diarrhoea after dairy.

The solution. Pre-digest the lactose using INDUSTRIAL lactase before selling the milk.

The process:

1. Lactase enzyme sourced from microbes (yeast or bacteria).
2. Enzyme IMMOBILISED on alginate beads (or similar support).
3. Beads packed into a COLUMN.
4. Milk PASSES THROUGH the column.
5. Lactase splits lactose → GLUCOSE + GALACTOSE.
6. These simpler sugars digestible by lactose-intolerant people.
7. Beads remain in column → reusable for many batches.

Why immobilised?

• Enzyme not lost in product → can be reused.
• Easy to switch enzyme batches.
• Product (milk) doesn't contain free enzyme.
• More cost-effective.

Other uses of immobilised enzymes:

• HFCS (high-fructose corn syrup): glucose isomerase converts glucose → fructose.
• Drug production.
• Wastewater treatment.

Worked qualitative. Why does lactose-free milk taste SLIGHTLY SWEETER than regular milk?

• Lactose isn't very sweet.
• Glucose + galactose (the digestion products) ARE sweeter.
• Same total sugar, sweeter flavour.
• Some manufacturers reduce other sugars to compensate.

Cambridge tip. Memorise: immobilised lactase + column + reusable. Cambridge marks each.

Components of biological washing powders:

Enzyme	Digests
Protease	Blood, sweat, food protein
Lipase	Greasy / oily stains
Amylase	Starch stains

How it works:

1. Wash starts; enzymes mixed with water.
2. Enzymes diffuse to stains.
3. Each enzyme breaks down its specific stain type → soluble products.
4. Soluble products wash away.

Advantages of biological detergents:

1. Lower temperature.

• Work at 30-40°C (vs 60-90°C for non-biological).
• SAVE ENERGY → lower bills, lower CO₂.

2. Better stain removal.

• Specifically target stain types.
• Especially good on protein (blood, food) and grease.

3. Less detergent needed.

• Enzymes catalytic — small amounts effective.

Limitations:

1. Temperature sensitive.

• Above ~60°C → enzymes DENATURE → stop working.
• Wash in cool/warm only.

2. Some people allergic.

• Protease can irritate sensitive skin.
• Enzymes encapsulated to reduce exposure but not zero risk.

3. Don't work on all stains.

• Rust, ink, dye stains aren't enzyme-substrates → unaffected.

Worked qualitative. Why does washing on the WRONG temperature programme RUIN biological detergent's effect?

• Above 60°C: enzymes denature → don't work.
• Below 20°C: enzymes work TOO SLOWLY in cold water.
• 30-40°C is the sweet spot for most biological detergents.
• That's why labels show 'optimum at 30-40°C'.

Cambridge tip. Always include 'WORK AT LOWER TEMPERATURES' as a key advantage. Cambridge marks energy saving.