KansasCindy's response gives the correct definition of blanching. However, the blanching time varies depending on the vegetable. Some require no more than 1-2 minutes; others may require 3 minutes or more. Thriftyfun has a guide to blanching on the website. You could also consult the Ball Book of Canning and Perserving for information.
If I remember right there are different directions for different types of food. As far as freezing tomatoes goes, all most of the people that I know, do is wash them, remove the stems and toss them in a plastic bag and then into the freezer. Then when they get a few more tomatoes they do the same thing, adding them to the previous bag.
Wiser ones might correct or add to my answer, but blanching as I understand such is merely placing the food (usually fresh vegetables or fruits) into a pot of boiling water for 1-2 minutes and then immediately submerging them into ice water to stop the cooking process. I use the process when preparing fresh vegetables (such as corn on the cob) for freezing. It also works well when preparing a batch of fresh tomatoes for processing as after you remove the tomatoes from the ice water, you can literally slide off the skins with your hands. Good Luck!
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