Apply modern methods to process food (milling, canning and bottling, fermentation, pasteurization, sterilization, dehydration, pickling)

Food processing transforms raw materials into safe, edible products with extended shelf life, while modern methods use advanced technologies to ensure precision, hygiene, and nutritional quality. This note covers the main modern processing techniques you need to understand: milling, fermentation, pasteurization, canning, sterilization, dehydration, and pickling.

Modern Methods of Food Processing

Milling

Milling is a fundamental processing method that reduces grains into usable forms like flour, grits, or meal. It involves several sequential steps that transform raw cereals into stable products.

Steps in milling:

1. Cleaning — removes stones, dust, husks, and foreign materials from grains to ensure food safety and protect equipment.

2. Conditioning — adjusts moisture content by adding or reducing water to soften the bran layer, making separation easier during grinding.

3. Grinding — mechanically breaks down grains using roller mills or other milling machines into smaller particles.

4. Sifting — passes ground material through sieves to separate fine flour from coarser particles and bran, ensuring uniform particle size.

5. Re-milling — returns coarse particles for further grinding to maximize yield and achieve desired fineness.

6. Collection and packaging — gathers the final product and by-products (bran, germ) for storage or further use.

Example: When milling maize in Tanzania, the grain is first cleaned to remove impurities, conditioned to the right moisture level, then ground using hammer mills common in local markets. The resulting maize flour is used for ugali, a staple food in many households.

---

Controlled Fermentation

Fermentation uses microorganisms (yeasts or bacteria) to break down carbohydrates into acids, alcohol, or gases without oxygen. This method enhances flavor, texture, safety, and nutritional value while preserving food.

The fermentation equation:

$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{energy}$

Where glucose is converted to ethanol and carbon dioxide.

Advantages of fermentation:

• Preservation — produced acids and alcohol inhibit spoilage microorganisms, extending shelf life
• Enhanced flavor — creates desirable tastes through organic acids, esters, and aromatic compounds
• Improved texture — softens foods and produces gas that acts as a leavening agent
• Nutrient enhancement — increases vitamin bioavailability and breaks down anti-nutritional factors
• Detoxification — reduces cyanide in cassava and phytates in cereals

Yoghurt preparation (work example):

Step	Procedure
1	Boil 1 L fresh milk for 10–15 minutes, then cool to ~40°C
2	Add 20 mL plain yoghurt (starter culture) as a bacterial inoculum
3	Stir gently and transfer to clean glass jars
4	Keep in a warm place (40–45°C) for 6–10 hours
5	Refrigerate to stop fermentation

Key points: The starter culture contains Lactobacillus bulgaricus and Streptococcus thermophilus bacteria that convert lactose (milk sugar) into lactic acid, thickening the milk and giving yoghurt its tangy flavor. Milk must cool before adding the starter because high temperatures would kill the beneficial bacteria. Temperatures below 40°C slow bacterial growth, while temperatures above 45°C can kill the culture.

---

Pasteurization

Pasteurization is a heat treatment that destroys harmful microorganisms while preserving the food's nutritional quality. It is applied to milk, juices, wine, and other beverages.

Types of pasteurization:

Method	Temperature	Time	Application
LTLT (Low-Temperature Long-Time)	63°C	30–60 minutes	Batch processing of milk
HTST (High-Temperature Short-Time)	72°C	15 seconds	Continuous flow processing
UHT (Ultra-High Temperature)	135–150°C	2–5 seconds	Long-shelf-life products

Advantages:

• Destroys pathogenic bacteria, reducing disease risk
• Extends shelf life by slowing spoilage
• Preserves most nutrients because heat is controlled
• Reduces reliance on chemical preservatives
• Cost-effective for large-scale production

Disadvantages:

• Some heat-sensitive vitamins (B and C) may be reduced
• Can alter flavor and texture of products
• Does not eliminate all microbial spores
• Risk of recontamination if handled poorly after heating

---

Pressure Canning

Pressure canning preserves food by heating it under high pressure at temperatures above water's boiling point (116°C/240°F). This method is essential for low-acid foods like vegetables, meats, and soups.

Steps in pressure canning:

1. Fill canner with 2–3 inches of water and heat until hot
2. Pack prepared food into clean jars, leaving proper headspace
3. Wipe jar rims, apply lids, and screw bands until fingertip tight
4. Place jars in canner, lock lid, and heat to desired pressure (usually 10 psi)
5. Maintain pressure for time specified in the recipe
6. Cool rapidly to prevent overcooking

Advantages:

• Extends shelf life for months or years
• Provides ready-to-eat convenience
• Makes seasonal foods available year-round
• Space-efficient storage

Disadvantages:

• Nutrient loss from high temperatures
• Time and labor intensive
• Requires specialized equipment (jars, pressure canner)
• Can cause flavor and texture changes
• Requires knowledge to ensure safety (risk of botulism if done incorrectly)

---

Sterilization

Sterilization destroys all microorganisms, including spores, by exposing food to high temperatures (110–121°C) for 15–30 minutes using pressurized steam in an autoclave or retort.

Examples of sterilized foods: canned peas, beans, tomatoes, corn, pineapple, peaches, mango, meat, fish, milk, and dairy products.

Advantages:

• Long shelf life (6 months to 2+ years)
• Ensures microbial safety
• Produces ready-to-eat convenience foods
• Reduces food waste through extended storage
• Preserves minerals, proteins, and carbohydrates

Disadvantages:

• May destroy heat-sensitive vitamins (C and B vitamins)
• Can change flavor, texture, or color
• Requires expensive specialized equipment

---

Dehydration

Dehydration removes water from food using natural or artificial methods, limiting microbial activity and enzyme action that cause spoilage.

Modern dehydration methods:

• Solar drying using solar dryers
• Hot air or tray drying
• Freeze-drying (sublimation)
• Vacuum drying
• Electric dehydrators with temperature control (35–74°C)

Examples of dehydrated foods: dried fish (catfish, anchovies), dried fruits (prunes, raisins), dried beef, milk powder, instant coffee, spices, and herbs.

Advantages:

• Extended shelf life through reduced moisture
• Reduced bulk and weight for easier transport
• Key nutrients remain stable when properly done
• Lower storage and packaging costs
• Quick cooking after rehydration

Disadvantages:

• Time and energy-consuming process
• Loss of heat-sensitive vitamins (C, B vitamins, antioxidants)
• Loss of fresh taste, texture, and flavor
• Risk of contamination if hygiene is poor
• Not suitable for high-fat foods

---

Pickling (Chemical Preservation)

Pickling uses acids (vinegar) or salt to create conditions that inhibit microbial growth. It is a form of chemical preservation that extends shelf life while adding distinctive flavors.

How it works:

• High acidity (low pH) interferes with microbial enzyme activity
• Salt creates osmotic pressure that draws water from microbial cells
• Organic acids like citric acid and acetic acid inhibit bacterial growth

Common pickled foods: cucumbers, onions, carrots, cabbage (as kimchi), fish, and meat.

Advantages:

• Enhanced flavor and color
• Simple and affordable method
• Significantly extends shelf life

Disadvantages:

• Health concerns from excessive salt or acidic foods
• Potential nutrient loss (sulphites lower vitamin B1)
• Some preservatives may cause allergies or digestive issues

---

Real-life application

In Tanzania, small-scale food processors and household cooks apply these modern methods regularly. For example, a woman running a small dairy business in Arusha can use pasteurization to process raw milk by heating it to 72°C for 15 seconds, then quickly cooling it before selling as safe, fresh milk—extending its shelf life from a few hours to several days while charging a premium price of around TSh 2,500 per liter compared to untreated milk. Similarly, fishers in Lake Victoria use dehydration (sundrying) to preserve omena (Lake Victoria sardines), reducing waste and creating a marketable product that can be stored for months and sold at local markets for extra income.