Food Physics and Chemistry

Chocolate and Ice-cream emulsions and colliods

The chocolate making process is steeped in tradition and secrecy. Since the discovery of the xocolatl plant in Aztec Mexico by the early explorers of the new world in the 16th century, companies have sought to secure market share by producing better tasting chocolate than their competitors.

Early chocolate was vastly different to the chocolate we know today. It was originally consumed by the Aztec and Mayan tribes of Central and South America as a drink - much like coffee. And also like coffee, it had a bitter, unpalatable taste. However, the physiological effects of drinking chocolate outweighed the bitter taste and the drink became extremely popular - to the extent that cocoa beans were used as currency until the 19th century.

Today, cocoa beans are grown in the tropical climates of Central and South America, Africa and south-east Asia. Total world production is in the order of 3 million tonnes per year. How cocoa beans are transformed into the delicious brown confectionery we are so familiar with is a long and interesting tale.

The journey begins on the cocoa farms. Once the cocoa pods are ripe, they are harvested and left in piles on the ground, covered with banana leaves, to ferment for up to 1 week. The harvest primarily takes place during the dry season (November - April) but also occurs in smaller quantities throughout the rest of the year. The fermentation reaction produces, principally, ethanol, acetic acid and lactic acid. These chemicals, and others, serve two functions. Firstly, they assist in the all-important flavour development of the finished product; and secondly, they kill the cocoa bean, which helps increase its storage life.

More important in improving the storage of the beans, however, is the next step: drying. The fermented beans contain around 17% water. Without removing most of this water, bacteria would thrive and almost certainly ruin the beans before they reach the production plants in Europe or America. There are several methods of drying, depending on how technologically advanced the farmers are. Traditionally, the beans were spread out in the sun and left until they were dry. More commonly today, the fermented beans are dried in machines such as roller dryers. The moisture content must be below 8% before the beans can be exported to the factories for further processing.

The next stage in the processing generally takes place in large factories that purchase cocoa beans from many different sources. The beans are cleaned to remove foreign objects like wood, string, nails, dust and dirt. The clean beans are then roasted.

Each cocoa bean contains a cocoa "nib" - analogous to a nut in a shell. The nib must be extracted from the shell before it can be processed. Roasting the whole bean loosens the shell, making the nib easy to remove. Although traditionally the whole bean was roasted prior to removal of the nib, today it is equally common to remove the nib and then roast it.

The roasted nibs are then ground to a fine powder called "cocoa liquor". The cocoa liquor is then either stored for future chocolate manufacture or pressed to separate the solid and liquid components of the liquor. The solid component is called cocoa powder and the liquid component is cocoa butter. The cocoa powder can be sold directly to consumers while the cocoa butter will be mixed with cocoa liquor to produce chocolate.

Individual chocolate makers then combine cocoa liquor and cocoa butter with other ingredients to produce chocolate.

In Britain, the most popular type of chocolate is milk chocolate, and the most common method of producing milk chocolate is via chocolate crumb or "crumb". Originally, milk powder didn't have a very long shelf life, and manufacturers found that the time of maximum chocolate demand didn't match the maximum milk powder supply. So they decided to mix the cocoa liquor, milk powder and sugar together and then cook them. The cooked crumb could then be stored for a long time due to the natural antioxidant preservatives in the cocoa. This cooking process also produces particular flavours to which consumers have grown accustomed and is the main reason that British chocolate tastes different from European chocolate.

To produce the final chocolate product, the manufacturer mixes the crumb with cocoa butter, other fats, flavouring and a touch of emulsifier in a large mixing vessel called a conche. The conche, which these days takes many forms, was invented in 1879 by Swiss chocolate maker, Rodolphe Lindt. So named because it resembled a conche shell, the conche quickly revolutionised the chocolate industry by producing much smoother, more delicious chocolate than had previously been possible. Conching can take anywhere from a few hours to a couple of days, depending on the type of conche.

The conched chocolate is tempered and crystallised. Tempering is necessary to give the finished product is firm feel and glossy appearance. Cocoa butter can naturally crystallise into 6 different crystal forms, but only form 5 has the right properties of appearance and texture. The tempering process is a method of encouraging the chocolate to crystallise into form 5.

Finally, the crystallised chocolate is packaged and sold.

Last year, Britons consumed more than 600 million kg of chocolate products in a chocolate market valued at more than £4 billion. With this much money at stake, manufacturers are continuously striving to gain an edge over their competitors.