ISF is an acronym for "Individually Slow Frozen". It is the opposite of IQF... which means "Individually Quick Frozen". But, before we learn about ISF, you may want to know about IQF first.
IQF foods have been around for a long time. The industrial process involves very quickly freezing foods individually, like various meats, seafood and vegetables, to name just a few.
The individually frozen foods do not touch each other during the freezing process, so they don't clump together during packaging. This allows the end user of the product to remove as much as needed from the container without thawing the entire contents.
Frozen food processors are equipped with machinery which simulate strong arctic blasts. In a matter of a few short minutes, foods can be preserved at sub-freezing temperatures. IQF shrimp, for example, can be frozen at temperatures approaching -50º F.
IQF foods are safer and last longer than foods which are preserved at just below 32º F. and it offers several advantages.
IQF prevents bacterial growth and allows stores, restaurants and consumers to use practical methods of storing foods safely and for longer periods of time.
Unfortunately, most of us cannot afford the large and expensive industrial blast freezers. We have to improvise by using our home freezers--which is not a problem.
This is where ISF enters the picture. It merely takes a little more time to achieve similar results, keeping in mind of course, that the foods we preserve in our home freezers will not attain the subfreezing temperatures of the blast freezers
This short video demonstrates how we can preserve sliced green tomatoes by 'slowly' freezing them on a cookie sheet lined with food grade waxed paper. And, we can do it in our refrigerator freezers.
Getting it done is a breeze... or, should I say a "freeze'?
However we describe it, this is a clever way of preserving sliced green tomatoes and it affords us the opportunity to have 'em year-round.
Hint: If you plan to use your ISF sliced green tomatoes in the not too distant future, then it's okay to save them in your freezer using zipper or resealable bags. If not, then it might be a good idea to vacuum seal them so they can keep for a longer period of time.
One other thing. It's important to not let the tomato slices touch each other during the freezing process so they may freeze individually. That way, as mentioned before, after packaging you can remove only the amount needed from the bag and save the rest for later.
I hope this helps.