Lyophilize - Freeze or Preserve? Quiz

Answer: Refrigeration

In 1756, William Cullen demonstrated the first known method of artificial refrigeration. In 1758 Benjamin Franklin and John Hadley found that by evaporating volatile liquids, the temperature of objects could be reduced quite rapidly - even past the freezing point of water. The first commercial refrigerated shipping occurred when a refrigeration unit was fitted to a 'Dunedin', a New Zealand vessel, in 1882 - this lead to a boom of dairy and meat between countries in the southern hemisphere, such as Australia and South America.

Refrigeration helps to preserve fresh foods by slowing the growth of micro-organisms that cause food to rot.

Answer: Freezing

Due to the fact that the moisture in the food is frozen, most bacterial species are unable to grow - thereby prolonging the life of the food.

Clarence Birdseye is probably best known as the person who brought snap-frozen food into the public awareness. He discovered that by freezing foods quickly the food tasted fresher and lacked the mushiness and dry consistency of those foods frozen using conventional (at the time) methods.

Answer: Vacuum packing

Reducing the oxygen around a food limits the growth of bacteria and fungi that require oxygen or air to breed or grow. Vacuum packing more commonly used for the storing of dry foods such as cured meats, cheeses and smoked fish.

Delicate foods such as potato chips (crisps) also use a type of vacuum packaging to protect them. Oxygen is removed from the packaging and an inert gas, such as nitrogen, is added instead.

Answer: Curing

Smoked and salt-cured meat date back to ancient times using different methods depending on where and how the producers lived. For example, Plains Indians would hang meat at the top of their tepee where the smoke from and internal fire was more likely to flavour and preserve the food.

Salting works by drawing the moisture from organisms on the foodstuff thereby impeding the growth of bacteria.

Some of the curing processes add to the flavour of the food, some don't. Part of the 'art' of curing food is getting the desired flavour at the end of the process.

Answer: Smoking

It is thought that smoking food goes back to primitive times (cavemen). It was discovered that meat dried using smoke was better preserved and had a different flavour to meat simply hung up to dry.

Smoking can be used either with or without pre-curing. It is also used in modern times as a cooking process (adding flavour to food to be eaten immediately) as well as a preservation method.

Different types of wood smoke can impart different flavours on the food being smoked. The addition of herbs and tea to the smoke is also a common practice for imparting flavour to the food (usually meat).

Answer: Pickling

There are two common types of pickling - chemical or fermentation pickling. Chemical pickling is where a food is submersed in an acidic liquid (and sometimes heated or boiled) before being stored in the same liquid. Usually vinegar or brine (salt water) is used as a pickling liquid. Fermentation pickling works by first salting the food to draw out excess moisture then letting the food sit at room temperature to ferment in its own juices and the lactic acid bacteria produced by the salting process.

Foods that are generally chemically pickled include cucumbers, gherkins, eggs and corned beef, while foods generally fermentation pickled are those such as sauerkraut (pickled cabbage), kimchi (Korean pickled vegetables) and nukazuke (Japanese pickled vegetables).

Answer: Canning or bottling

Canning and bottling both include cooking food and sealing it in a container. The container is then heated (or boiled) to kill off or sterilise any remaining bacteria. Depending on the type of food, other preservatives or acidic agents are added to help with the process.

Canning and bottling are mainly used to preserve fruits and vegetables but is also used to preserve other foodstuffs, like processed meats such as Spam.

Answer: Jellying

Have you ever heard of jellied eels? They are preserved using this process. Basically a food is cooked and put into a dish (usually the desired final shape of the food), before having a meat stock poured over it. When the stock cools it sets due to the natural gelatin found in the meat it was made from. The stock can be clarified before pouring over the food to be preserved, resulting in a clear jelly-like substance when cooled. The final product is just like a savoury jelly with food (such as vegetables, eggs, etc) set inside it.

Answer: Irradiation

High energy electrons, x-rays or gamma rays are used to kill bacteria, mould and other nasties such as insects, in a food preserving process known as irradiation. The process is also referred to as 'cold pasteurisation' as the result is similar yet no heat is involved in the process (as in 'normal' pasteurisation).

As irradiation doesn't kill viruses, the food being treated has to be of high quality in the first place. Although it can be said for most food-preservation techniques that it is preferred that food is of high quality before treatment.

Answer: Burial

Low light, low temperatures and low oxygen below ground are the factors that can help to preserve buried food. Burial can be combined with other types of preservation (such as fermentation, curing or smoking), and soils that have a high salt content, are dry or are frozen are preferable to use for this process.

Biopreservation is using and controlling natural microbes to prolong the life of food, hurdle technology is the use of several different techniques to preserve food, and blast chilling is a method of cooling food very quickly (similar to freezing yet quicker again).