# Aerated chocolate

Aerated chocolate is a type of chocolate that intentionally contains gas, forming bubbles. Aerated chocolates have a lower density than regular chocolates and consumers experience a smoother melt. Aerated chocolate was first brought to market in 1935 by British chocolate maker Rowntree's under the brand Aero. Other companies ignored the process's patent, and today multiple producers make aerated chocolate.
There are four types of aerated chocolate. The main, seen in Aero has large bubbles and is produced under a vacuum or by beating gas into liquid chocolate under pressure. Aerated chocolate with tiny bubbles uses the same beating gas method, but uses nitrogen. Aerated chocolates containing long tubes of air are extruded rather than moulded. A final type, an aerated chocolate held together by a skeleton of solid particles rather than fats are produced by forming an emulsion between ingredients and sugar dissolved in water, and then reducing the water content by freeze drying or regular evaporation and drying.

## History

In 1935, British chocolate manufacturer Rowntree's brought the first aerated chocolate, Aero, to market. The process for making the new chocolate was covered by a broad patent, capturing a variety of tablets including ones embedded with additions such as nuts. Rowntree's initially promoted aerated chocolate as more digestible than solid chocolate, though this was objected to by rival chocolate manufacturer Cadbury. Further to these objections, Cadbury contested the validity of the patent itself. In September 1936, chocolate makers Fry's released an aerated Crunchie bar made entirely of chocolate. They justified this move, saying it did not breach the patent as it was not a block but a bar. After Fry's launched a second aerated chocolate in August 1937 called Ripple, Rowntree agreed to allow chocolate manufacturers to manufacture aerated chocolates after June 1938 if they committed to paying Rowntree a sum upon releasing new aerated chocolate lines and a 0.5% royalty on sales. After this period, Cadbury only released an aerated chocolate in markets in overseas dominions where Aero was not established. Nestlé-produced aerated chocolates included a chocolate called Bubblo, made in the UK for export to New Zealand under a New Zealand patent.
By 1936, Aero was being successfully exported to Australia, and The Hershey Company purchased the Aero patent in May 1937, later altering the flavor and texture for the American palate. During 1937, Rowntree's produced machinery for production in Éire, Canada and South Africa, as well as for the companies Lindt and Van Houten. In the 1970s, biscuit manufacturers began using micro-aeration to process chocolate for moulded products. In 1981 or 1983, Cadbury released Wispa, an aerated chocolate made using a secret, non-patented process. While its launch was a success, during a period where it was temporarily withdrawn to resolve manufacturing difficulties, Rowntree developed and launched a chunky Aero which was still on the market as of 2008. Wispa was discontinued in the early 2000s, and Cadbury did not sell aerated chocolate until releasing Dairy Milk Bubbly in October 2007 following an internet campaign and reintroducing Wispa permanently in 2008. Today, Aero is manufactured by Nestlé.

## Types

There are four types of aerated chocolates that have been sold:
* Chocolate containing large, visible bubbles. Bubble diameters are between 0.05–3.0 mm (0.002–0.118 in), and the product is around half the density of regular chocolate. It is the most common type; Aero is a prominent example.
* Micro-aerated chocolate. The bubbles of this chocolate are so small as to be almost imperceptible to the naked eye. Micro-aerated chocolates are primarily used to coat chocolate biscuits in an effort to reduce the percentage of chocolate by weight.
* Chocolate containing long, continuous tubes of air. These chocolates are made by extruding semi-set or solid chocolate. Cadbury used to sell this type of chocolate under the brand Spira.
* Chocolate held together by a skeleton of solid particles, particularly sugar, rather than fat which typically binds chocolate together. This chocolate is used as an addition on items such as ice-creams and cakes after it is cut or roughly milled. For a time, this was sold on the Japanese chocolate market under the brand Poff.

## Characteristics

Aerated chocolate has a lower density than conventional chocolate, giving it a greater volume for the same weight, a softer texture and an eating experience of having a smooth melt. Biting into some aerated chocolates produces an audible crunch, a phenomenon understood to be a product of its structure and texture. Upon entering the mouth, some aerated chocolates generate a "fragile mouth feel" and quickly melt when chewed. These phenomenon stem from the greater surface area, and intensify the flavor. The crispiness has been attributed to the presence of larger bubbles. Micro-aerated chocolates have a creamier taste and melt faster than regular chocolate, while aerated chocolates held together by solid particles rather than fats can have an extremely low density (0.1–0.3 g/cm$^3$ (0.0036–0.0108 lb/cu in)), allowing them to dissolve quickly in the mouth. Chocolate foamed with nitrogen—and especially with nitrous oxide—have the most intense taste due to the larger bubbles these gases produce.

## Production

Aerated chocolate containing large bubbles is produced via two methods. In the first, melted chocolate is put under a vacuum, where it foams up. As the chocolate cools, and the fats within the chocolate set, the foam structure remains. Sometimes gases such as carbon dioxide are introduced into the mixture before it is placed under the vacuum. While the method easily permits additions such as nougat or nuts, difficulty keeping production hygienic means the second method is more frequently used. This second method involves working gases into liquid, tempered chocolate under high pressure. Carbon dioxide is mainly used, although others include nitrous oxide. Any gases that do not dissolve are dispersed as bubbles through the chocolate using a beater. As the chocolate is released from the high pressure conditions, the bubbles expand, foaming the product; through this the amount of pressure directly impacts bubble size. The setting chocolate is deposited in a molded shell, after which the set interior is capped with liquid tempered chocolate. Factors that affect bubble size include qualities of chocolate, such as viscosity, rate of setting and ingredients (e.g. emulsifiers and milk fats). The type of gas, pressure differences and rate and change.
Micro-aerated chocolate is created using the method of beating gases in under high pressure. Unlike aerated chocolates produced with large bubbles, micro-aerated chocolate has nitrogen beaten into the mixture. The resulting chocolate, different not only in bubble size but also flavors and textures, possibly arises from the different solubility of gas. Aerated chocolates containing long tubes of air are also created using this technique, but their distinction comes from how the aerated chocolate is extruded rather than set in a molded shell. The final type, those held together by a skeleton of solid particles, are produced using water evaporation methods. In the first of these, sugar is dissolved in water. This solution is emulsified with cocoa liquor and milk solids, which is evaporated and then dried using industrial machinery, until the product contains less than 2% water. In the second, chocolate is emulsified with liquid chocolate and set and then freeze dried, removing the water.

### Research

A major source of bubble instability is when a wide variety of sizes of bubbles are created, gases in smaller bubbles diffuses or disperses into larger bubbles. This is due to their respective Laplace pressures. As of 2023, technologies to control bubble size, distribution and movement were difficult to employ during production. "Advanced" research was underway, including by companies such as Nestlé. In 2013, Chinese scientists announced results from a study using phospholipids derived from soybeans to aerate cocoa butter.