I am going to assume zero previous knowledge of food preservation while writing this post. I am just a little ahead of the learning curve than someone who knows nothing about it, so I feel highly qualified to write on this basis! This post is not intended to be exhaustive or scientific – it’s to help you establish a basic understanding of the hows and whys of food preservation.
You preserve food by addition, subtraction, or pressure. Don’t worry, this isn’t going to turn into a maths lesson. You will have already come across all these different methods during your life even if you don’t realise it.
You can preserve food by adding salt, sugar, and/or acidity in the form or vinegar or lemon/lime juice. Preserved foods such as jams and pickles are made by adding sugar, salt, and/or acidity. Everyone’s favourite, strawberry jam, uses a 4:3 ratio of strawberries to sugar. Bread and butter pickles (see my favourite recipe here) shows the strategic use of salt, acid, and sugar to preserve cucumbers for later consumption.
How do these additions work? Acid is obvious – when you drop something in acid it burns, which is what happens to any microbes which could spoil your food or make you sick.
Salt and sugar are strongly attracted to water – to give you a rough mental image, they “suck” the water out of the cells of the bad microbes before they have a chance to spoil your food. (Just for fun, what is the only human food stuff that requires no preservation? Answer at the end of this post!) Salted foods and fruit preserves have been part of the human diet for millennia, just look at all the references to salted pork, beef, jams, and so on in any historical novel.
You can preserve food by removing all the water. Drying has also been a part of our food preservation efforts for most of human history. Just check any grocery store for the herbs and spices, you will be staggered by how many there are! Jerky is a dried meat that will last for months without refrigeration, showing the power of this form of food preservation.
Yes, I am setting homework!
The USDA has an incredibly useful resource available for free. Check them out at their website and have a leisurely read through – it is a very good use of your valuable time!
(Trivia answer: honey does not go off or moldy!)