The way in which the unique Aero bubbles are added is a top-secret process closely guarded by Nestle Rowntree.
We can tell you, however, that there are approximately 2,200 bubbles in one Aero chunky bar.
Secret details may be absent but the broad answer is in Rowntree’s British patent GB 459583 from 1935.
The chocolate is heated until it is in a fluid or semifluid state, then it is aerated, for example using a whisk, to produce many tiny air bubbles distributed throughout the chocolate.
This is poured into molds and the air pressure greatly reduced as the chocolate is cooled. The reduced air pressure causes the tiny bubbles to grow and gives the finished chocolate its frozen bubbles appearance. The solid chocolate coating on the surrounding surfaces of the bar is placed into the mold before the aerated fluid chocolate is poured in.
The patent gives no clues on how the bubbles are prevented from rising to the surface during manufacture, but this may be due to the high viscosity of the semifluid chocolate and the rapid rate of cooling.
Patents provide a great source of technical information.
It has been suggested that 80 percent of technical disclosures appear in patents and nowhere else. You can view and print GB 459583 using the service on the Patent Office web-site. The service provides an interface to British and European patent offices for you to search their databases.
US patent 4272558 and British patent GB 480951 from 1938 is on “Improvements in Confections for Eating or for Making Into Beverages” filed by Sydney Phillips and Arthur Whittaker. This patent contains information on making bubbles in molten chocolate with pressurized gas and then discharging the gas through a nozzle.
It states: “The releasing of the chocolate into a region at atmospheric pressure causes the gas to escape from or expand within the chocolate, giving the chocolate a porous, cellular, honeycomb-like open structure.”
It’s not the chocolate answer that your reader was looking for, but I was once told that a soap manufacturer used the same process to make floating soap. The experiments were a technical success, inasmuch as the soap floated, but the product was not commercially viable because it dissolved too quickly.
David Bailey of Brookes Batchellor patent attorneys in Tunbridge Wells, Kent, UK, also picked up on another patent, GB 459582, and so did Armen Khachikian of the British Library’s patents information section. This was filed by Rowntree on the same day as the one mentioned above and contains the Aero concept.
The chocolate makers clearly knew what they were about. Khachikian points out that eight days before the patent was lodged, the Aero name was trademarked.
Although British patents expire 20 years after they are filed, the trademark on the name Aero is still in force.