Many people enjoy planting gardens and eating fresh, homegrown produce in the summer. For people who want to preserve their garden vegetables and eat them another time, freezing is a viable option. The color, flavor and texture of the produce is often maintained when it is frozen, and the freezing process is easy and less time consuming than canning.
Blanching is necessary to inactivate enzymes. The enzymes are proteins in the plant that help with the ripening and maturing process. If vegetables are not blanched, this maturation process can continue (at a very slow pace) in the freezer. To blanch vegetables, they are placed in boiling water or steamed for a period of time and then placed in ice water.
Blanching for the correct amount of time is important. Over-blanching can result in a cooked product with less flavor, color and nutrients. Under-blanching can actually speed up enzyme activity making the food undesirable for eating. To find out exactly how long each vegetable needs to be blanched, download the MU Extension publication Quality for Keeps: Freezing Vegetables (GH1503).
The goal when freezing vegetables is to have the smallest ice crystals possible because they cause less damage to cell walls. To achieve this, the food needs to be frozen quickly to produce a a lot of small ice crystals. To assure quick freezing, many people set the freezer at -10 degrees F, 24 hours before they are going to freeze food. Once the food is frozen, the thermostat can be set back to 0 degrees.
Be sure not to overload the freezer with unfrozen food. Overloading will result in slow freezing, which makes for larger ice crystals and more cell damage. You should only add the amount of food that will freeze within 24 hours — about two to three pounds of food per cubic foot of freezer space. (A cubic foot is an area that is one foot long by one foot wide by one foot deep.)
For best results, maintain a temperature of 0 degrees F in the freezer. Quality deteriorates quickly at temperatures above zero. The same loss of quality of frozen green beans stored at 0 degrees F for one year will occur in three months at 10 degrees F, in three weeks at 20 degrees F and in five days at 30 degrees F.
Ten months is the recommended freezer storage time for fresh vegetables.