Almost all raw vegetables must be blanched before being frozen. Blanching is rarely done for fruit.
At first blush, it could seem counter-intuitive that pre-cooking by blanching before freezing helps keep most vegetables “fresher”, but it actually does.
Over time, enzymes in produce can cause loss of colour, flavour, nutrition and texture. Freezing produce as-is does not inactivate many of these enzymes, only slow them down. In some cases vegetables will go soft; in others, they will toughen. Nutrition can also be impacted. The food will be safe to eat: but, the quality loss can be noticeable so people may not want to eat it.
Blanching inactivates the enzymes and helps dramatically reduce these quality issues.
Blanching times can vary by vegetable and by size of the piece being blanched.
Overblanching damages the quality. Underblanching is worse than no blanching, as it stimulates the enzymes and speeds up their spoilage work.
Blanching can be done in either boiling water or steam. Some vegetables have recommendations for both; some for only one or the other.
Note that steam blanching times are longer on paper, but that’s not necessarily the case in actual practice. Water blanching times only start from when the water returns to a boil (which in practice can take a while), while steam blanching times start when the lid is put back on the pot, so when steam blanching, you get to start the timing much faster.
Note that recommended blanching times for dehydrating will often differ from blanching times for freezing.
Blanching times for freezing vegetables
This table is just meant as a handy summary for quick time reference. Sources used are from 2014 onwards.
For actual detailed freezing directions for specific items, please see a reputable source such as one of the books mentioned below.
Where blanching recommendations differ, we present the differing recommendations for you to decide.
Codes
BBB: Ball Blue Book. Muncie, Indiana: Healthmark LLC / Jarden Home Brands. Edition 37. 2014. Freezer blanching tables on pages 154 to 157.
SETP: So Easy to Preserve. Elizabeth L. Andress and Judy A. Harrison. University of Georgia Cooperative Extension. Bulletin 989. Sixth Edition. 2014. Freezer blanching tables on pages 279 to 280.
Reminders
- All procedures assume thorough washing first;
- All procedures assume any required prep such as trimming, peeling, etc, first;
- Steam blanching times start as soon as the lid is replaced on the pot of boiling water;
- Blanching times must be adjusted for altitude.
Altitude adjustment
Blanching times table for freezing vegetables
| Item | Boiling Water (mins) | Steam (mins) | Source | Notes |
|---|---|---|---|---|
| Artichoke hearts | 7 | SETP, BBB | ||
| Asparagus stalk - small | 2 | 3 | SETP | BBB says water blanch 1 ½ minutes |
| Asparagus stalk - medium | 3 | 5 | SETP | BBB says water blanch 2 minutes |
| Asparagus stalk - large | 4 | 6 | SETP | BBB says water blanch 3 minutes |
| Beans (Snap, green or wax) | 3 | 5 | SETP, BBB | |
| Beans (Butter, Lima or pinto) - Small | 2 | 3 | SETP | BBB says water blanch 1 minute |
| Beans (Butter, Lima or pinto) - Medium | 3 | 5 | SETP | BBB says water blanch 2 minutes |
| Beans (Butter, Lima or pinto) - Large | 4 | 6 | SETP | BBB says water blanch 3 minutes |
| Beans (Green soybeans aka edamame) | 5 | SETP | ||
| Beets | Cook until tender | SETP, BBB | Cook fully with skin on, then cool, peel and slice or dice | |
| Broccoli * | 3 | 5 | SETP | 1 ½ inch (4 cm) pieces |
| Brussels sprouts - small | 3 | 5 | SETP, BBB | |
| Brussels sprouts - medium | 4 | 6 | SETP, BBB | |
| Brussels sprouts - large | 5 | 7 | SETP, BBB | |
| Cabbage, shredded | 1 ½ | 2 ½ | SETP, BBB | BBB says for wedges, blanch 3 minutes |
| Carrots -- small whole | 5 | 8 | SETP | BBB says cut carrots 3 minutes, whole carrots 5 minutes |
| Carrots -- diced, sliced or spears | 2 | 3 | SETP | |
| Cauliflower | 3 | 5 | SETP | BBB says small pieces 3 minutes, large 4 minutes |
| Celery | 3 | SETP | ||
| Corn on the cob - small cobs * | 7 | 10 | SETP | |
| Corn on the cob - medium cobs | 9 | 13 | SETP | |
| Corn on the cob - large cobs | 11 | 16 | SETP | |
| Corn - kernel or cream | 4 | 6 | SETP | Blanching times are for whole cobs. After blanching, cut off kernels and freeze |
| Eggplant (aka Aubergine) | 4 | 6 | SETP, BBB | Both say when water blanching, add 125 ml lemon juice per 4 litres of blanching water / ½ cup per 1 gallon |
| Fiddleheads | 2 | |||
| Greens -- Collards | 3 | 5 | SETP, BBB | |
| Greens -- All others | 2 | 3 | SETP | |
| Herbs (fresh) | Do not blanch | BBB | ||
| Jerusalem Artichokes (aka sunchokes) | 3 to 5 | SETP | ||
| Kohlrabi - whole | 3 | SETP | ||
| Kohlrabi - cubes | 1 | SETP | ||
| Mushrooms -- whole, buttons or quarter | 9 | SETP, BBB | BBB says water blanch small, whole mushrooms 4 minutes | |
| Mushrooms -- slices | 5 | SETP | BBB says water blanch slices 3 minutes | |
| Okra pods -- small | 3 | 5 | SETP, BBB | |
| Okra pods -- large | 5 | 8 | SETP, BBB | |
| Onions -- whole | 3 to 7 | SETP, BBB | SETP and BBB say need to be blanched until centre is heated | |
| Onions -- slices | 10 to 15 seconds | SETP | ||
| Parsnips | 3 | 5 | SETP, BBB | SETP says peel, cut into cubes |
| Peas -- edible pods | 2 to 3 | 4 to 5 | SETP, BBB | BBB says 2 for small, 3 for large |
| Peas -- blackeye | 2 | SETP, BBB | BBB says small 1 minute, larger 2 minutes | |
| Peas -- English garden peas | 1 ½ to 2 ½ | 3 to 5 | SETP, BBB | |
| Peanuts -- Green in shell | 10 | BBB | ||
| Peanuts -- Shelled | Do not blanch | BBB | ||
| Peppers (Sweet) -- Halves | 3 | 5 | SETP | BBB says do not blanch. |
| Peppers (Sweet) -- Slices | 2 | 3 | SETP | BBB says do not blanch. |
| Potatoes -- white | 3 to 5 | 5 to 8 | SETP, BBB | |
| Potatoes -- sweet | Cook fully | SETP, BBB | ||
| Pumpkin | Cook fully | SETP | BBB says cook by steaming | |
| Rutabaga | 3 | 5 | SETP | |
| Squash -- Chayote | 2 | SETP | ||
| Squash -- Spaghetti | Cook fully | BBB | Cook fully by roasting, then extract pulp strands with a fork and freeze theose | |
| Squash -- Summer | 3 | 5 | SETP, BBB | |
| Squash -- Winter | Cook fully | SETP, BBB | ||
| Tomatoes -- Green | Do not blanch. | BBB | Wash, core, slice, freeze separating slices. | |
| Tomatoes -- Red | Cook into sauce or juice | BBB | ||
| Turnips | 3 | 5 | SETP, BBB | SETP says peel, cut into cubes |
| Zucchini (aka courgette) | 3 | 5 | SETP | |
Notes
Broccoli: Ball Blue Book says water blanch small pieces for 3 minutes, large pieces for 4 minutes
Corn on the cob: Ball Blue Book gives water blanching times by diameter: 1 ½ inches (4 cm) for 6 minutes, 2 inches (5 cm) for 8 minutes, 10 minutes for any that are thicker
Fiddleheads: Leave whole, water blanch 2 mins, discard blanching water, drain, cool, pack, freeze. [Do not attempt to pressure can.] Source: Health Canada. [2]Health Canada. Fiddlehead safety tips. 2015. Accessed Oct. 2017.
Peppers: Ball Blue Book says roast and peel pimientos, and NOT TO BLANCH other hot or sweet peppers
Tomatoes: The following method can be used to freeze tomatoes whole, no blanching. Wash first. Then “cut away the stem scar. Place the tomatoes on cookie sheets and freeze. Tomatoes do not need to be blanched before freezing. Once frozen, transfer the tomatoes from the cookie sheets into freezer bags or other containers. Seal tightly. To use the frozen tomatoes, remove them from the freezer a few at a time or all at once. To peel, just run a frozen tomato under warm water in the kitchen sink. Its skin will slip off easily.” [3]Henneman, Alice. Freezing Raw Tomatoes – With or Without Their Skins. University of Nebraska-Lincoln Extension Service.
Blanching fruit for freezing
Fruit is not generally blanched before freezing.
Rhubarb is an exception for which blanching is presented as an option. So Easy to Preserve says, “Heating rhubarb in boiling water for 1 minute and cooling promptly in cold water helps retain color and flavor.” [4]So Easy To Preserve. Page 275.
For fruit, the treatment options are more about how the fruit is packed: syrup pack, sugar pack, or a sugar-free pack such as dry-pack or pectin-pack. See So Easy To Preserve, 2014, pages 263-267 for detailed information, as well as the Freezing Fruit pamphlet from the University of Georgia.
Further reading
Blanch Vegetables Before Freezing. Metzgar, Karma. University of Missouri Extension. 2009.
Freezing Fruit. Judy A. Harrison and Elizabeth L. Andress. University of Georgia. July 2000. FDNS-E-43-4.
Vegetable blanching directions and times for home freezer storage. Driessen, Suzanne [Ed.]. University of Minnesota Extension Service. 2015. (Link valid as of October 2017)
References