No one knows exactly when a frozen dessert was first produced. Ancient manuscripts tell us that the Chinese liked a frozen product made by mixing fruit juices with snow – what we now call water ice. This technique later spread to ancient Greece and Rome, where the wealthy in particular were partial to frozen desserts.
Frozen dessert and Ice cream were made possible only by the discovery of the endothermic effect. Prior to this, cream could only be chilled but not frozen. It was the addition of salt, that lowered the melting point of ice, which had the effect of drawing heat from the cream and allowing it to freeze. The processing and production of Frozen dessert has drastically changed from then to now, with the addition of advance technologies and process lines in Ice cream. Before studying the process and manufacturing of Ice cream, a basic understanding on the raw materials and its chemistry is important to understand Ice cream on a larger scale.
Raw Materials and Ingredients
The ingredients used in frozen dessert production are:
Fat makes up about 10 to 15% of the frozen dessert mix. The fat gives creaminess and improves melting resistance by stabilizing the air cell structure of the frozen dessert. Milk fat is replaced in the case of frozen dessert by vegetable fat, where refined or hydrogenated (hardened) coconut oil and palm kernel oil are most commonly used.
- Milk solids non-fat (MSNF)
MSNF consists of proteins, lactose, and mineral salts derived from whole milk, skim milk, condensed milk, milk powders, and/or whey powder. In addition to its high nutritional value, MSNF helps to stabilize the structure of ice cream due to its water-binding and emulsifying effect. The same effect also has a positive influence on air distribution in the ice cream during the freezing process, leading to improved body and creaminess.
In a well-balanced recipe, the quantity of MSNF should always be in proportion to the water content. The optimal level is 17 parts MSNF to 100 parts water:
- Sugar/non-sugar sweetener
Sugar is added to increase the solids content of the frozen dessert and give it the level of sweetness consumers prefer. Ice cream mix normally contains between 12 to 20% sugar. The consistency of the ice cream can also be adjusted by selecting different types of sugar. This makes it possible to produce ice cream that is easy to scoop.
In the production of sugar-free ice cream, sweeteners are used to replace sugar. Aspartame, acesulfame K and sucralose are the most commonly used sweeteners in ice cream and are applied in conjunction with a bulking agent such as maltodextrin, poly-dextrose, sorbitol, lactitol, glycerol, or other sugar alcohols.
Emulsifiers and stabilizers are typically used as combined products at dosages of 0.5% in the ice cream mix. Traditionally, these products were produced by dry blending, but today integrated products are preferred due to the improved dispersion and high storage stability.
Emulsifiers are substances that assist emulsification by reducing the surface tension between two phases. Emulsifiers bind the fat portion and non-fat portion of the ice cream top create a consistent matrix for the ice cream.
Stabilizer is a substance that can bind water when dispersed in a liquid phase. This is called hydration and means the stabilizer forms a matrix that prevents the water molecules from moving freely. Most of the stabilizers utilized for ice cream are large molecules derived from seeds, wood, or algae/seaweed. Stabilizers are used in ice cream production to increase the viscosity of the mix and create body and texture. They also control the growth of ice crystals and improve melting resistance.
Flavors are a very important factor in the customer’s choice of ice cream and can be added at the mixing stage or after pasteurization. The most popular flavors are vanilla, chocolate and strawberry.
Natural or artificial colors are added to the mix to give the ice cream an attractive appearance. Local legislation exists in most countries regarding the use of colors in food.
- Other ingredients
Ripples (sauces) are incorporated in frozen desserts for taste and appearance. They can also be applied for pencil filling and top decoration.
Dry ingredients are either added through an ingredient dozer or as top decoration matter on cones, cups, and bars. A great variety of products are used: chocolate, nuts, dried fruit pieces, candies, cookies, Smarties, caramel pieces, etc.
The production of Ice cream and frozen desserts are pretty much similar. The difference is that vegetable oil is used for preparing the mix in frozen desserts. After the mix preparation, the further steps are the same.
The major steps in the production process are:
- Mix Preparation
This is one of the most crucial steps in the production of Ice cream or Frozen Dessert. The tank-stored raw materials are heated and blended to form a homogenous mix that is pasteurized and homogenized. Large production plants often have two mix tanks for each flavor with a volume corresponding to the hourly capacity of the pasteurizer, in order to maintain a continuous flow to the freezers.
The dry ingredients, especially the milk powder, are generally added via a mixing unit, through which water is circulated, creating an ejector effect that sucks the powder into the flow. Before returning to the tank, the mix is normally heated to 50 to 60°C to facilitate dissolution. Liquid ingredients such as milk, cream, liquid sugar, etc. are measured into the mix tank.
- Pasteurization and Homogenization
In large-scale production, the ice cream mix flows through a filter to a balance tank. From there it is pumped to a plate heat exchanger, where it is pre-heated to 73-75°C. After homogenization at 14 to 20 MPa (140-200 bar), the mix is returned to the plate heat exchanger and pasteurized at 83 to 85 °C for about 15 seconds.
The pasteurized mix is then cooled to 5°C and transferred to an ageing tank.The purpose of pasteurization is to destroy bacteria and dissolve additives and ingredients. The homogenization process results in uniformly small fat globules which improve the whipping property and texture of the ice cream mix.
The mix must be aged for at least 4 hours at a temperature of 2 to 5°C with continuous gentle agitation. Ageing allows the milk proteins and water to interact and the liquid fat to crystallize. This results in better air incorporation and improved melting resistance.
- Freezing and Packaging
Continues freezer is the device used to whip a controlled amount of air into the mix and to freeze a significant part of the water content in the mix into a large number of small ice crystals.
The ice cream mix is metered into the freezing cylinder by a gear pump. At the same time, a constant airflow is fed into the cylinder and whipped into the mix by a dasher. The refrigerant surrounding the cylinder generates the freezing process. The layer of the frozen mix on the inside cylinder wall is continuously scraped off by the rotating dasher knife, and a second gear pump drives the ice cream forward either to an ingredient feeder or a filling machine.
The output temperature is -8 to -3°C depending on the type of ice cream product, where 30 to 55% of the water is frozen into ice crystals depending on the composition of the mix formulation.
The increase in volume following the incorporation of air in the mix is called overrun, and is normally 80 to 100%, corresponding to 0.8 to 1 liter of air per litre of the mix.
- Hardening and Storage
A filling machine fills the frozen dessert directly from the freezer into cups, cones, and containers of varying designs, shapes, and sizes. Filling takes place through a time-lapse filler, a volumetric filler, or an extrusion filler. In the case of extrusion filling, a cutting mechanism is provided. Decoration with various ingredients is possible, including nuts, fruits, chocolate, jams, or gumballs.
Lids are put on the packs before leaving the machine, after which they are passed through a hardening tunnel where final freezing to -20°C product core temperature takes place.
Before or after hardening, the products can be manually or automatically packed in cartons or bundles. Plastic tubes or cardboard cartons can be filled manually through a can-filling unit equipped to supply single or twin flavors.
Ice cream has come a long way since the first snow cone was made. Innovations in a variety of areas over the past century have led to the development of highly sophisticated, automated manufacturing plants that churn out pint after pint of ice cream. Significant advances in fields such as mechanical refrigeration, chilling and freezing technologies, cleaning and sanitation, packaging, and ingredient functionality have shaped the industry.
New developments in ice cream freezer technology will be likely in the future as freezers are better engineered to control the complex microstructures in ice cream. Current freezers are designed to form ice, create air bubbles, and destabilize fat globules in the short time that ice cream spends in the scraped surface freezer. A better understanding of how to optimize each of these structure developments will lead to more efficient freezer operations.