Ice cream quality is largely determined by its microstructure. Generally the finer the air bubble structure and the smaller the ice crystals at the point of consumption, the smoother the structure and the creamier the taste of the ice cream. In other words, ice cream microstructure is strongly influenced by processing.
Traditional methods of industrial ice cream processing rely on continuous freezers followed by hardening in a hardening tunnel. Today, a relatively new technology - low temperature extrusion (LTE) - is starting to gain popularity in the industry. LTE was originally invented in the ‘80s, later developed and made available in the ‘90s. Commercial low temperature freezers (single screw) are produced and sold by Tetra Pak under the Tetra Hoyer DeepBlue trade name.
Conventionally processed ice cream is drawn from the freezer at -5 to -6 deg C. This is when about half of the water content would have been frozen into ice crystals. The remaining water available is frozen during the subsequent hardening process (-40 deg C) and cold storage (-30 deg C).
A conventional freezer is a scrape-surface heat exchanger (SSHE), where the minimum drawing temperature for a standard ice cream formulation is typically -7 deg C. The problem here, though, is the freezer’s double whipping and freezing role. When the temperature of ice cream is lowered below the freezing point of the mix, more water freezes into ice and ice cream viscosity increases.
This viscosity increase causes a corresponding increase in friction heat created by the whipping action, which means more energy has to be removed from the system in order to lower the ice cream temperature. When the drawing temperature reaches a certain minimum point, the whipping energy on the ice cream equalizes the amount of energy that the cooling media is capable of removing. As a result, a further reduction in the ice cream drawing temperature is not possible.
Low temperature freezers
Using a low temperature freezer after the first conventional freezer thus creates an opportunity to achieve lower drawing temperatures of -12 to -15 deg C for a standard ice cream formulation. A low temperature freezer is either a single or twin screw extruder, which operates at very low rotor speed of around 15-30 rpm and has no evident whipping function. The ice cream is gently conveyed through the freezing cylinder, resulting in a finer microstructure with smaller ice crystals and air bubbles.
Danisco has invested in a pilot-scale low temperature freezer. With this equipment, it is possible to produce small batches of low temperature extruded ice cream products to determine ice cream optimization possibilities using emulsifier and stabilizer systems and/or by adjusting recipes and production parameters.
The company’s investment is an effort to assist ice cream producers that are either planning to acquire or have acquired low temperature extrusion equipment.
One of the ongoing mega trends in the food segment is the health and nutrition trend, which sees consumers focusing more and more on natural health and wellness, weight management and healthy snacking. This is reflected in the ice cream industry by the growing number of low, no and reduced fat ice cream products on the market. Over the past year, more than 10 percent of all new ice cream products were launched with one of these claims. A regional breakdown provided by Mintel GNPD reveals that, in North America, about 25 percent of all new ice cream launches were low/no/reduced fat, compared to 13 percent in Australia/New Zealand, seven percent in Europe, three percent in Latin America and two percent in Asia.
The history of ice cream with low/no/reduced fat claims is illustrated in Chart 1. Almost no launches were recorded by Mintel in 1997, increasing from 1998 to1999 and from 2002 to 2005.
Solutions to processing low-fat ice-cream
Because modern consumers do not wish to compromise on taste and texture, the challenges when producing low/no/reduced fat and/or sugar ice cream are significant. Potential problems in low-fat ice cream include:
- iciness
- weak body (thin)
- lack of creaminess
- fast melting
- short quality shelf life
- lack of form stability
- shrinkage
These can be overcome by using appropriate processing, formulation and dedicated emulsifier and stabilizer systems.
The small ice crystal sizes and fine air cell structure achieved by low temperature extrusion improves the smoothness and creaminess of ice cream products. Creating the impression of a higher fat content, low temperature technology is perfect for low/no/reduced fat ice cream. In addition, the small ice crystals prolong product shelf life significantly as the time taken for them to grow to a sensorily detectable size is delayed.
To obtain an optimal texture, the ice cream formulation must also be correctly balanced. This can be achieved using fat replacers such as polydextrose, a low calorie bulking agent marketed by Danisco as Litesse. Its fat replacing and bulking properties compensate for some of the functionality lost when fat is taken out.
Emulsifier and stabilizer combinations also improve texture significantly. A new range of emulsifier and stabilizer blends from Danisco is specially designed for low fat applications. Called Cremodan 1100 LF IcePro, the range protects ice cream from quality defects due to temperature fluctuations during storage and distribution. It also raises the perception of a higher fat level in low fat ice cream by increasing smoothness and reducing iciness for a rich, full-bodied product.
Both Unilever and Nestle have been using LTE for more than 10 years. In the US, Nestle uses the technology actively in marketing their light brand, Slow Churned – the name referring to the LTE process where the ice cream is conveyed slowly through the low temperature extruder. Many other manufacturers in the US have similar marketing concepts. Names such as Double Churned, Home Churned, Cold Churned and Smooth Churned are today widely used for the modern wave of light ice cream products.
