Neil Baker of Kaikoura Suburban School asks :-
How is hokey pokey in ice cream made round?
Fiona Nyhof, a product development scientist in the Department of Food Science, University of Otago, responded.
Hokey pokey is a type of hard candy. Home-made hokey pokey is made from sugar, golden syrup and sodium bicarbonate (or baking soda). Commercially manufactured hokey pokey ingredients include sugar, glucose syrup, butter, sodium bicarbonate, salt, gelatine, water and flavour. All the ingredients play a functional role to achieve the familiar golden appearance, crunchy yet slightly gooey honeycomb texture and unique flavour of hokey pokey.
Glucose syrup, butter, salt and flavour are substitutes for golden syrup because they enable good process control with commercial sized batches. Sodium bicarbonate is a foaming agent that releases carbon dioxide gas when it reacts with other ingredients in the mixture. The gas is responsible for all the tiny bubbles you see in hokey pokey. Gelatine helps set the foamy structure, absorb moisture and maintain the texture of hokey pokey during storage in ice cream.
Most candy is made by boiling up mixtures of glucose and sucrose sugar solutions to high temperatures and then controlling crystallization during cooling. As water evaporates during boiling the sugars in solution become more concentrated and the temperature of the boiling sugar mixture increases. The temperature increase is proportional to the concentration of dissolved sugars (solute) which is a key indicator for process control. At 113C the sugar concentration is around 85 per cent, the so called "soft ball" stage suitable for making fudge. As the water is removed the texture of the cooled candy changes from softer to more brittle, at 144C-149C the sugar concentration approaches 98-100 per cent, the so called "hard crack" stage. At this stage the moisture content is very low (less than 2 per cent).
Hokey pokey is processed to the hard crack stage. The crunchy texture of hokey pokey is the result of a phase transition during cooling from a concentrated hot foamy sugar syrup mixture to a solid, non-crystalline or glassy like foam structure. Glucose in the formulation helps prevent crystallization of this type of candy. The intense sweet taste and golden colour results from concentration and slight caramelisation of the sugars.
To form the hokey pokey pieces the hot foamy mixture is cooled in specially designed moulding equipment. For commercial production it is passed through two opposing rollers that each have hemispherical impressions in the surface. The result is round balls that go crunchy when cold.