Soft-ice is a frozen whipped product generally similar to ice cream, but made with water or skimmed milk mixed with a flavoring preparation. Materials for soft-ice mixes, usually in powder form, are commercially available in a variety of flavors. Because soft-ice is lower in calories and cholesterol than true ice cream, it is favored by many persons who are on restricted diets or who are concerned about their diets.
Heretofore, soft-ice has mainly been prepared with the use of large and expensive apparatus that simultaneously whips and freezes the mixed material. Such apparatus is suitable for making the product in large batches and is not adapted to being scaled down to a size suitable for domestic use. Furthermore, soft-ice does not keep well, and therefore those who wish to enjoy it must usually eat it at the place where it is made.
There have been prior efforts to provide a small domestic appliance for making soft-ice, as shown for example, by Swiss Pat. No. 624,278. Usually, an essential feature of such prior machines was a means for cooling the soft-ice mix to solidify it by freezing. In commercial scale machines this function was performed by a refrigeration cooling unit, but in domestic appliances, wherein compactness and low cost are important, cooling was usually effected by means of a cold pack such as a water-salt mixture that was frozen in a deep freezer or a refrigerator before being loaded into the soft-ice machine.
In practice it has been found that domestic soft-ice machines that rely on a cold pack do not enable the user to produce a uniform, good quality soft-ice at all times. Furthermore, such machines are neither compact nor convenient to use.
An alternative to freezing the soft-ice mixture during whipping is to freeze it before whipping, as suggested in U.S. Pat. No. 3,738,619, to Shirae. This means that the mixture is frozen (as in a deep freezer) into a hard, solid chunk having about the consistency of an ice cube, and is presented to an agitator which comminutes and whips the frozen material. It is perhaps not surprising that prior apparatus operating on this principle has tended to produce a rather poor quality product which, at best, contained a sprinkling of hard, ice-like granules and which was practically never a uniformly smooth whipped product.
Freezing the soft-ice mix before it is whipped offers several important advantages, provided the frozen mass can be converted into a dessert that has the consistency of good quality ice cream. The frozen mixture can be stored indefinitely in a freezer, in compact one-serving containers, to be whipped immediately before consumption. Thus, mixing of the material can take place at any convenient time, and whipping can be accomplished with a compact and relatively inexpensive appliance that need not incorporate refrigeration apparatus nor provision for a cold pack. Of course, the crucial factor is the provision of a method and means for whipping the frozen mix, whereby a uniformly smooth and non-granular whipped product is consistently produced; but heretofore the art has not known how to accomplish this.
It has been found that one element needed for the purpose is an agitator or comminuting device that will move rapidly across the surface of the frozen chunk of material, as by rotation, and at the same time advance very slowly into the frozen material, so that the material is processed little by little, but very thoroughly and completely. The need for producing this type of agitator motion poses the problem of providing a simple, compact and inexpensive mechanism for accomplishing it. The above mentioned U.S. Patent to Shirae discloses apparatus wherein manual force was applied to a rotating agitator to advance it axially into the body of ice. Since the manual force applied to the agitator was indeterminate and variable, the quality of the finished product tended to be dependent upon the skill, experience and luck of the operator. Apparently the patentee did not appreciate that rotational speed of the agitator and rate of its axial advance are parameters that are critical to the attainment of a uniformly smooth product, and it also appears that the provision of automatic means for axially advancing the agitator was not obvious to the patentee.
The problem of providing for exactly the required movement of the agitator is further complicated by the desirability of providing an automatic operating cycle for the mechanism, whereby the agitator will be retracted from the container when the operation is completed. Preferably, too, the motor that drives the agitator should be automatically shut off at the end of the operating cycle, to conserve energy, prevent excessive working of the whipped product, and serve as a signal that processing is completed. In a household appliance, these objectives must necessarily be achieved in apparatus that is compact and inexpensive but is nevertheless sturdy and easy to clean as well as simple to operate.
Although the configuration of the agitator and its rates of rotation and axial advance have been found to be important, they are not the only factors involved in the achievement of a satisfactory soft-ice, and the present invention involves, in part, the discovery of a further critical factor.