CHAPTER 1
The Story of Ice Cream
WHAT IS ICE CREAM?
Ice cream is an enormously popular food. The term 'ice cream' in its broadest sense covers a wide range of different types of frozen dessert. The main ones are
• dairy ice cream – a frozen, aerated mixture of dairy ingredients, sugars and flavours.
• non-dairy ice cream – made with milk proteins and vegetable fat.
• gelato – an Italian-style custard-based ice cream that contains egg yolks.
• frozen yoghurt – which may contain lactic acid organisms, or simply yoghurt flavour.
• milk ice – similar to ice cream, but unaerated and containing less dairy fat.
• sorbet – fruit based, aerated sugar syrup that contains neither fat nor milk.
• sherbet – similar to a sorbet, but containing some milk or cream.
• water ice – frozen sugar syrup with flavour and colour, such as an 'ice lolly'.
• fruit ice – similar to water ice, but made with real fruit juice.
What these all have in common is that they are sweet, flavoured, contain ice and, unlike any other frozen food, are normally eaten in the frozen state.
The legal definition of ice cream varies from country to country. In the UK 'ice cream' is defined as a frozen food product containing a minimum of 5% fat and 7.5% milk solids other than fat (i.e. protein, sugars and minerals), which is obtained by heat- treating and subsequently freezing an emulsion of fat, milk solids and sugar (or sweetener), with or without other substances. 'Dairy ice cream' must in addition contain no fat other than milk fat, with the exception of fat that is present in another ingredient, for example egg, flavouring, or emulsifier. In the USA, ice cream must contain at least 10% milk fat and 20% total milk solids, and must weigh a minimum of 0.54 kg l-1. Until 1997, it was not permitted to call a product 'ice cream' in the USA if it contained vegetable fat.
Ice cream is often categorized as premium, standard or economy. Premium ice cream is generally made from best quality ingredients and has a relatively high amount of dairy fat and a low amount of air (hence it is relatively expensive), whereas economy ice cream is made from cheaper ingredients (e.g. vegetable fat) and contains more air. However, these terms have no legal standing within the UK market, and one manufacturer's economy ice cream may be similar to a standard ice cream from another.
Most people are very familiar with the appearance, taste and texture of ice cream and there are many recipes for making it in cookery books. However, few people know why certain ingredients and a time- consuming preparation process are required. The answer is that ice cream is an extremely complex, intricate and delicate substance. In fact, it has been called "just about the most complex food colloid of all". The science of ice cream consists of understanding its ingredients, processing, microstructure and texture, and, crucially, the links between them. This requires a whole range of scientific disciplines, including physical chemistry, food science, colloid science, chemical engineering, microscopy, materials science and consumer science (Figure 1.1).
The ingredients and processing create the microstructure, which is shown schematically in Figure 1.2. It consists of ice crystals, air bubbles and fat droplets in the size range 1 µm to 0.1 mm and a viscous solution of sugars, polysaccharides and milk proteins, known as the matrix. The texture we perceive when we eat ice cream is the sensory manifestation of the microstructure. Thus, microstructure is at the heart of the science of ice cream, and forms the central theme running through this book.
To describe the science of ice cream, it is first necessary to describe some of the physical chemistry and colloid science that underpins it; these are laid out in Chapter 2. Chapters 3 and 4 cover the ingredients and the ice cream making process respectively. Chapter 5 focuses on the production of various types of ice cream product. The physical and sensory measurements used to quantify and describe it are discussed in Chapter 6, and the microstructure, and its relationship to the texture, is examined in Chapter 7. Finally, Chapter 8 describes a number of experiments that illustrate the science of ice cream, which may be performed in the laboratory, classroom or kitchen. We begin, however, by looking at where and when ice cream was invented, and how it has evolved into the huge range of products eaten by billions of people all around the world today.
THE HISTORY OF ICE CREAM
Ice cream as we recognize it today has been in existence for at least 300 years, though its origins probably date much further back. The history of ice cream is full of myths and stories, which have little real evidence to support them. A typical 'history' begins with the Roman Emperor Nero (AD 37–68) who is said to have eaten fruit chilled with snow brought down from the mountains by slaves. Elsewhere, Mongolian horsemen are reputed to have invented ice cream. They took cream in containers made from animal intestines as provisions on long journeys across the Gobi desert in winter. As they galloped, the cream was vigorously shaken, while the sub-zero temperature caused it to freeze simultaneously. The expansion of the Mongol empire spread this idea through China, from where Marco Polo reputedly brought the idea to Italy when he returned from his travels in 1296. It has been claimed that ice cream was introduced to France from Italy when the 14-year-old Catherine de Medici was married to the Duc d'Orleans (later Henri II of France) in 1533. Her entourage included Italian chefs who brought the recipe for ice cream with them. The secret of making ice cream remained known to only a few. So precious was it that Charles I of England is said to have offered his French chef a pension of £500 per year to keep his recipe secret.
However, historical research has found little evidence to support any of these stories. The only mention of ice in connection with Nero comes from Pliny the Elder in the first century AD, who records the discovery that water that has been boiled freezes faster and is healthier. There is no mention of ice cream in any of the manuscripts describing Marco Polo's travels. Indeed, modern historians doubt that he even reached China. It is unlikely that Catherine's chefs knew how to make ice cream since, at that time, the method of refrigeration by mixing ice and salt was known in Europe only to a handful of scientists. Nor is there any documentary evidence for Charles' chef.
We cannot be absolutely sure of exactly who invented ice cream, or where and when. In reality, the history of ice cream is closely associated with the development of refrigeration techniques and can be traced in several stages related to this.
1. Cooling...
