According to the Office of National Statistics, in 2008 almost 40% of homes in the UK had a dishwasher, up from around 25% in 1998. It is tempting to think of machine dishwashing as comparable to hand washing of dishes but in fact it is a much more complex process and involves a great deal more chemistry.
Hand dishwashing relies mostly on mechanical effort - continuing to brush or sponge (with the help of hot water and a detergent), until the dishes appear clean. With machine dishwashing, mechanical effort counts for less, and the chemistry has to do the cleaning. However, the conditions for machine washing can be both hotter and more alkaline that could be withstood by human hands.
Here we will look at some of the chemistry that goes on inside the dishwasher and relate it to chemistry that you already know. The science of dishwasher products is complex and we can only cover the basics here.
Did you know?
Josephine Cochrane invented the modern dishwasher in 1886.
Cochrane was a wealthy socialite whose servants kept chipping her fine china while hand washing it. She developed a rack and water jet system that was first demonstrated at the 1893 Chicago World Fair.
Figure 1: A product from the Finish range
How does a dishwasher work? (1 of 2)
Before we consider the chemistry, we need to understand the mechanics of a dishwasher, Figure 2. This is essentially very simple.