Characteristics
Soft serve is generally lower in milk-fat (3% to 6%) than ice cream (10% to 18%) and is produced at a temperature of about −4 °C compared to ice cream, which is stored at −15 °C. Soft serve contains air, introduced at the time of freezing. The air content, called overrun, can vary from 0% to 60% of the total volume of finished product. The amount of air alters the taste of the finished product. Product with low quantities of air has a heavy, icy taste and appears more yellow. Product with higher air content tastes creamier, smoother and lighter and appears whiter. The optimum quantity of air is determined by the other ingredients and individual taste. It is generally accepted that the ideal air content should be between 33% and 45% of volume. More than this and the product loses taste, tends to shrink as it loses air and melts more quickly than that with less air.
All ice cream including soft serve must be frozen quickly to avoid crystallization. With soft serve, this is accomplished by a special machine at the point of sale. Pre-mixed product (see definitions below) is introduced to the storage chamber of the machine where it is kept at 3°C. When product is drawn from the draw valve, fresh mix combined with the targeted quantity of air is introduced to the freezing chamber either by gravity or pump. It is then churned and quick frozen and stored until required.
Pre-mix can be obtained in several forms:
- Fresh liquid that requires constant refrigeration until needed. It can be stored for 5 to 7 days before spoiling by bacterial contamination. Quality can be severely compromised by bacterial contamination and handlers must exercise caution to maintain quality.
- A powdered mix. This is a dried version of the liquid mix. It has the advantage of easy distribution and can be stored for long periods of time without spoiling. Water must be added prior to being churned and frozen. The disadvantage is that water quality cannot be guaranteed and some operators can put too much water in to make it go further. It also should be refrigerated to 3 degrees Celsius prior to use, as airborne and waterborne bacteria can infect it immediately and can grow quickly if the product is warm. Residual bacteria in the refrigerated storage compartment can also be activated by warm product being introduced.
- Ultra Heat Treated mix, a liquid that has been sterilized and packed in sealed, sterile bags. It can last a very long time without refrigeration and can be poured into the soft serve freezer immediately upon opening. However it should be refrigerated to 3 degrees Celsius prior to use for the same reasons outlined above. At the time of opening, quality can be guaranteed and bacterial counts are zero. Where it is available, health authorities consider it the safest form of soft serve mix on the market. It was first developed for commercial use in New Zealand in 1988 in a joint venture between Tatua Foods, a dairy company and Bernie Cook, owner of Blue Boy, a mobile franchise network.
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