have no photomicrographs of fish similar to those I've shown for vegetables. But I imagine that such photographs would show some differences in cellular structure as a result of various speeds of freezing. Whether or not such differences are important to the ultimate user, however, is a key question.

Freezing with LN or other cryogenic materials produces a quality that is probably closer to fresh quality for most products than any other process now being used commercially, so far as physical appearance is concerned. The photomicrographs prove this statement for certain vegetables, at least. But application of this fact is subject to two qualifications:

1. For many, and perhaps most products, the physical difference between the instantly and the quickly frozen is not so apparent, and in some cases is virtually nonexistent,
2. One may not need to go to "instant" freezing to obtain all the quality improvement practical in commercial operation. Sensory appraisals at the U.S. Department of Agriculture's Western Utilization Research and Development Division, have demonstrated that green beans frozen quickly in a very cold air stream have a quality that is hardly distinguishable from LN frozen beans. At the present stage in our research program, it would appear that vegetables such as beans, asparagus, and peas frozen in 4 or 5 minutes may be good enough for even the most exacting demand.

Very little is generally known about how fast freezing must really be to obtain a desired quality. We have used cryogens because of their availability and because they do an excellent freezing job. But they maybe too costly, especially so if a less costly method can do an equally satisfactory job.

In fast freezing, it is the rate of heat removal that is important, not the temperature of the freezing medium. Extremely rapid freezing takes place in brine or liquid dichlorodifluoromethane (Freon 12) at minus 3 5 degree C (minus 3 1 degree F). The rate approaches that of freezing with LN or solid C02. Extremely high air velocity in air-blast freezing coupled with fluidization of the product can also greatly speed the rate of freezing. Coil temperature below those now accepted as the limit of economical operation might prove feasible. If air at minus 30' to 40 degree C. freezes too slowly but air at minus 600, 700, or even 80 degree C. would do the job, it might be less costly to provide air at these temperatures than to jump all the way to minus 196 degree C. (minus 325 degree F) at a cost of 3 cents -a pound. If the cost of air-blast freezing is now 0.3 or 0.4 cent a pound, we could double or triple that cost and still be way below the more costly methods.