In 1883, American socialite Josephine Cochrane was suddenly widowed and left with increasing debts. However, she had an idea that she hoped would turn her fortunes around. After years of hosting large dinner parties and seeing her valuable dishes become chipped during handwashing, she became convinced that people needed a better way to clean dishes.
Cochrane poured the little money she had left into building a prototype. She eventually presented her dishwashing invention at the Chicago World’s Fair. Her design became an important first step towards the modern dishwasher, whose basic structure remains surprisingly similar to hers.
When a dishwasher is started, it fills a small basin with water and heats it to approximately 60°C. The pre-wash cycle then begins. A circulation pump sends high-pressure water into rotating spray arms. The water shoots through angled nozzles, causing the arms to spin and spray the dishes.
The water returns to the basin, where a turbidity sensor measures how dirty it is by checking how much light can pass through it. Based on this information, the dishwasher adjusts the washing time and water temperature accordingly.
During the main wash cycle, detergent is released into the water. After the dirty water drains away, clean water heated to around 68°C is circulated for a final sanitising rinse. This water is generally at least 10 degrees hotter than the hottest water from a typical kitchen sink and can eliminate most foodborne bacteria. Some dishwashers then begin an optional drying cycle.
The effectiveness of a dishwasher depends partly on the type of detergent used. Dishwasher detergent is normally sold as liquid, powder, or pods. The main ingredient in each form is a surfactant. Surfactants are special molecules that attach to food residue with one end while pulling it towards the water with the other.
Dishwasher detergents may also contain enzymes and bleach. Enzymes break food down into smaller pieces that surfactants can remove more easily. Bleach disinfects dishes and removes stains.
Liquid detergent can contain either bleach or enzymes, but usually not both because bleach breaks down enzymes in liquid form. Powder detergents solve this problem by covering powdered enzymes in protective wax, allowing them to work alongside bleach. Dishwasher pods keep their different ingredients separate by using a thin plastic film. However, this plastic may have environmental consequences. Some studies suggest that it biodegrades within a few months, while others indicate that it remains in the environment for much longer.
The condition of the dishwasher can also influence its performance. A dirty dishwasher or filter may cause the turbidity sensor to believe that the dishes are dirtier than they really are. Consequently, the machine may run an unnecessarily long washing cycle.
Although it may seem counterintuitive, rinsing dishes before putting them in the dishwasher can also cause problems. If dishes have already been thoroughly rinsed, the sensor may detect very little dirt and select a shorter cycle. This may not be long enough to remove stubborn food that is still stuck to the dishes.
Additionally, detergent enzymes are specifically designed to attach to food residue. For this reason, the best practice is to scrape large pieces of food from dishes rather than rinse them completely.
Using a dishwasher can also save water. Dishwashers recycle water during the washing process and typically use between three and five gallons per load. This is approximately the same amount of water used when a kitchen tap runs for up to two and a half minutes. Therefore, if handwashing would take longer than that, using the dishwasher may be more water-efficient.
However, handwashing is still appropriate in some situations. The extremely hot water in a dishwasher can warp wooden objects and certain types of plastic. It may also damage the seals in travel mugs and food-storage containers. Sharp knives can become dull because of dishwasher detergent, and they may even damage the machine.
Energy use is another consideration. A standard dishwasher cycle uses approximately the same amount of energy as leaving a television switched on for 12 hours.
There are clearly situations in which handwashing makes more sense. However, when you are faced with a large number of dishes after a dinner party, a dishwasher can provide a welcome break.
