Ice cream is an extremely popular dairy product in India. The ice cream market is growing at a phenomenal 12%, and the current market size is estimated at about Rs 4000 crore. Ice cream generally contains several ingredients including fat, milk solids-not-fat, sweeteners, stabilisers, emulsifiers, water, flavours, and colours.
Mongolians are reputed to have invented ice cream. The expansion of the Mongol empire put this idea through China, from where Marco Polo reputedly brought the idea to Italy, from where it became popular worldwide. Agnes Marshall, regarded as the "queen of ices" in England, is credited with popularising ice cream as a regular snack through her popular books. Ice cream thus became popular throughout the world in the later part of the 20th century after refrigeration became cheap and common.
Blending the ingredients
Ice cream manufacture involves blending the ingredients, pasteurising, homogenising, ageing, and hardening. Pasteurisation is the biological control point for safety in the process chain, and it is designed for the destruction of pathogenic microorganisms. The mix is also homogenised to form a fat emulsion by breaking down or reducing the size of the fat globules found in the mix (milk or cream) to less than 1 µm.
Homogenisation reduces size of fat globules, increases surface area, gives a smoother texture and richness, increases resistance to melting, better air stability and so on. As clustering of the fat is reduced, a thinner and more rapidly whipped mix is evolved. The high temperature homogenisation facilitates more efficient breaking up of the fat globules and reduces fat clumping.
The ice cream mix is then aged to allow the fat to cool down and crystallise, and for the proteins and polysaccharides to fully hydrate. While freezing, the mixture is deliberately stirred to incorporate air, and is cooled below the freezing point of water to prevent ice crystals from being formed. The result is a smooth and semi-solid foam that remains solid at very low temperatures. Thus, ice cream consists of ice crystals, air bubbles and fat droplets in a viscous matrix of sugars, milk proteins and polysaccharides.
Hardening is done in the freezers, where about 50% of its water in the mix is frozen. There are rotating blades inside the barrel that keep the ice scraped off the surface of the freezer, while the dashers inside the machine help to whip the mix and incorporate air. The remainder of the water is frozen in a blast freezer or during storage at temperatures below -20°C. The ice crystals start off as a ‘hexagonal shape, and more ice is added, the crystals grow, and the bigger they get, and a crunchier final product is obtained in this method. Ageing improves whipping qualities of mix and also the body and texture of ice cream.
Though most people are very familiar with the appearance, taste and texture of ice cream, and many recipes are there for making it, a great deal of science is involved between the microscopic structure and the macroscopic properties of ice cream. This is because ice cream is an extremely complex, intricate and delicate food. The texture we perceive when ice cream is eaten is the sensory manifestation of the microstructure.
Freezing Ice Cream using Liquid Nitrogen
Using liquid nitrogen (LN2) to make ice cream is nothing new. Agnes Marshall suggested the use of liquid nitrogen to make ice cream in her book titled Ices Plain and Fancy: The Book of Ices published in the 19th century. This is the earliest reference we have on the use of LN2 for making ice cream. Today, there are lots of chefs playing around with LN2 in the kitchen.
Though the use of liquid nitrogen for freezing ice cream was well-known, the technology was not available in India until a couple of years ago.
As published in a leading daily (“Have you tried nitrogen ice cream?” dated August 28, 2015), this fairly new concept of ice cream arrived in the capital with ‘Niice Cream’ in Hauz Khas Village. Today, a few companies have set up such customised ice cream making facilities in Hyderabad, Coimbatore and in other southern states. Culinary nitrogen in liquid form is also available.
As liquid nitrogen is added to a liquid such as an ice cream mixture, it cools the liquid inside the ice cream mix rapidly as it boils away, producing a cloud of gas. The freezing process is quite a spectacle. Liquid nitrogen provides a great, dazzling, magical, special effect. The secret to the creamy ice cream is all in the rapid freezing of the mixture, which is provided by liquid nitrogen. The goal of using LN2 is to reduce the ice crystals in ice cream. This process also may not require the stabilisers used in commercial ice cream. Without the pockets of extra air whipped in, the ice cream made by this method does not melt easily. The ice cream will be better in on microbiologically quality too.
However, there is a negative to using LN2 to make ice cream. It could be dangerous if one is not careful. Because the liquid-to-gas expansion ratio of nitrogen is about 700 times at 20°C, a tremendous amount of force can be generated if liquid nitrogen is rapidly vapourised.
Is this Ice Cream Safe?
Prof. Peter Barham from the University of Bristol's School of Physics says liquid nitrogen is "simply the harmless gas nitrogen, which has been cooled to such a low temperature that it becomes a liquid." Therefore, if jumping into the molecular gastronomy pond is something that piques your interest, liquid nitrogen ice cream is a good gateway recipe. Also, this process is similar to aerating ice cream with air because about 78% of air is nitrogen.
Preparation from Powder Mixes
As a great deal of science is involved between the microscopic structure and macroscopic properties of ice cream, preparation is extremely complex and delicate. It is difficult to make good ice cream at home because of the complexity and number of ingredients involved. Alternatively, readymade ice cream powders not only offer convenience to consumers but also add energy efficiency in its processing, storage and supply chain. The development of dried ice cream powder is of relatively recent origin.
ICAR-National Dairy Research Institute, Bengaluru, has developed a technology for preparation of ice cream powder from milk standardised to 8.2 and 8.8% fat and SNF. The standardised milk containing the stabilisers and emulsifiers was concentrated to 30% total solids, homogenised and spray-dried into powder. The dried powder was blended with 15% of finely ground sugar to get ice cream powder having 2.4% moisture, 26.8% fat, 23.2% protein, 3.7% ash and 43.9% total carbohydrates. The product has reasonably good reconstitution and flow properties. Sensory quality of ice cream made from dry mix was comparable to that made by conventional method.
