Brief description

Sterilization is any process that removes, kills, or deactivates all forms of life and other biological agents present in a specific surface, object, or fluid. Unlike pasteurization, which only reduces the microbial load, sterilization aims for the total elimination of all microorganisms, including highly resilient bacterial spores.

Use / Function

Surgery and Medicine: Preventing life-threatening infections by ensuring instruments and environments are free of pathogens.
Microbiology: Preparing growth media for studying specific microbes without contamination.
Food Preservation: Canning and bottling food to be shelf-stable for years.
Water Purification: Making water safe to drink in extreme conditions.

Operating principle

Sterilization works by terminally damaging the proteins, membranes, or genetic material of microorganisms:

Moist Heat (Autoclave): Using steam under pressure. This is the most effective method because pressure allows steam to reach temperatures above boiling (121°C or 250°F), which kills even the toughest spores.
Dry Heat: Using an oven or direct flame. Requires higher temperatures and longer times than moist heat.
Chemical: Using strong oxidizers or poisons (e.g., ethylene oxide, high-concentration bleach, or hydrogen peroxide).
Radiation: Using ultraviolet (UV) light or ionizing radiation to shatter DNA.
Filtration: Physically removing microbes from liquids or gases using membranes with tiny pores (0.22 microns).

How to implement it

1. Boiling (Disinfection)

Submerge objects in boiling water (100°C) for at least 20-30 minutes.
Note: This kills most bacteria but may not kill all spores. It is disinfection, not true sterilization.

2. Pressure Cooking (Basic Autoclave)

Place instruments in a pressure cooker.
Maintain 15 psi (approx. 121°C) for at least 15-20 minutes. This is the gold standard for improvised medical sterilization.

3. Flaming

Pass metal instruments (like needles or scalpels) through a hot flame until they glow red. This is immediate and effective for small items.

4. Chemical Soaking

Submerge clean instruments in 70-90% Alcohol or a 10% Bleach solution for at least 30 minutes.

Materials needed

Heat Source: Fire, stove, or furnace.
Pressure Vessel: Pressure cooker or custom-built autoclave.
Chemicals: Alcohol, Bleach, or hydrogen peroxide.
Indicator: Autoclave tape or chemical indicators to confirm that sterilization temperature was reached.

Variants and improvements

Tyndallization: Boiling for 20 minutes, letting it sit for a day, and repeating three times. This allows spores to germinate into vulnerable bacteria which are then killed in the next boil.
Fractional Sterilization: Used when materials cannot withstand high pressure.
Modern Autoclaves: Computer-controlled cycles with vacuum stages to ensure steam penetrates every crevice.

Limits and risks

Re-contamination: A sterilized object becomes unsterile the moment it touches a non-sterile surface or is exposed to open air.
Material Damage: High heat can dull sharp edges (scalpels), melt plastics, or corrode certain metals.
Explosion Risk: High-pressure steam vessels are dangerous if not properly maintained and vented.
Chemical Toxicity: Many sterilizing chemicals are toxic to humans and must be rinsed off with sterile water before use.