A courgette plant can produce more fruit than one household wants to eat in August. Freezing is an excellent way to avoid throwing the surplus away, but there is a catch: courgettes contain plenty of water. After freezing and thawing, they will not have the firm bite of a freshly picked vegetable. That is fine for soup, pasta sauces and baking, provided you prepare them for the right job.
In the United States, courgettes are usually called zucchini. The National Center for Home Food Preservation (NCHFP) provides tested freezing instructions under its guide to summer squash. The method for sliced pieces differs from the method for grated courgette destined for baking.
Choose young courgettes rather than oversized marrows
Select fruit with tender skin and firm flesh. Very large mature courgettes can have a coarse interior, many developed seeds and a more watery texture.
Wash the outside under cool running water and inspect for damage. Trim off the stem and blossom ends. Discard any fruit showing mould, substantial softness or a bitter taste.
An unusually bitter courgette should not be eaten or preserved. Bitter flavours can indicate potentially harmful cucurbitacins in some cucurbits, and cooking or freezing is not a reliable solution.
Decide how you will use it later
If you make vegetable soup, curry or a simple tomato-and-courgette sauce, slices or chunks are convenient. If you bake courgette cake, muffins or quick breads, grated courgette is easier to measure and mix.
Think in portions. A bag containing the amount you normally add to one family dish is more useful than one enormous container of chopped vegetables.
Before starting, clear enough freezer room for the packages. You also need a pan for blanching, a bowl of iced water, clean draining equipment and freezer-safe bags or boxes.
Cut slices of an even thickness
The NCHFP's guidance is to select young, tender summer squash, wash it and cut it into approximately 1.3cm (½-inch) slices.
Uniform pieces blanch more evenly. Don't cut one half of the batch into wafer-thin rounds and the rest into large chunks, then expect the same timing to suit both.
You generally do not need to peel tender-skinned courgettes. The skin helps give the pieces some structure after cooking and keeps preparation simple.
Water-blanch sliced courgette for three minutes
Bring a large pan of water to a full boil. Add a manageable portion of the sliced courgette and allow the water to return to boiling.
The NCHFP gives a three-minute water-blanching time for sliced summer squash. Follow its general blanching directions for when to start the timer and use enough water to cope with the vegetable load.
Blanching reduces enzyme activity that can damage frozen quality. It is not meant to cook the slices completely soft, so avoid extending the time merely because they don't look ready to serve.
Cool the slices straight away
Transfer blanched slices into iced or very cold water immediately. The aim is to stop the cooking process before the courgette becomes overdone.
Drain well and spread on a clean cloth or kitchen paper to remove surplus moisture. Wet vegetables are more likely to clump into large frozen masses.
Don't allow the drained slices to sit for a long time at room temperature. Pack as soon as they've cooled and the excess water has been removed.
Pack slices with the right headspace
The NCHFP recommends packing sliced summer squash with about 1.3cm (½ inch) headspace, sealing the container and freezing promptly.
A rigid container is useful if you want to avoid crushing the pieces. Freezer bags also work when they're suitable for the intended contents and closed tightly.
Label with the date, approximate weight and intended use. If you freeze both slices and grated courgette, make the distinction obvious; after a few months, the packages may look very similar.
Grated courgette needs a different method
For baking, the NCHFP describes grating young courgettes, then steam-blanching small quantities for one to two minutes, until translucent.
Do not simply assume that the three-minute water blanch for slices is the right process for grated pieces. The finely shredded vegetable heats differently and can absorb more water if boiled.
Steam blanch in manageable batches using suitable equipment, and keep the preparation hygienic. Work promptly so the shreds do not stand in a warm bowl for an extended period.
Portion grated courgette before freezing
Pack the grated courgette into measured recipe-sized portions. If your favourite muffin recipe uses 200g, weigh that amount into an appropriate freezer container.
The NCHFP says to leave about 1.3cm headspace, cool the filled containers in cold water, then seal and freeze. Use containers that are suitable for the temperature changes involved.
A measured pack removes guesswork on baking day. It also helps prevent unnecessary partial thawing of a larger frozen block.
Deal with liquid after thawing
Grated courgette often releases a surprising amount of water when it thaws. The NCHFP specifically advises discarding the liquid before using grated zucchini for baking if it appears watery.
Check what your recipe expects. Some recipes are written for well-drained grated courgette, while others include the vegetable's natural moisture in their ingredient balance.
Use the portion consistently. If you drained one batch heavily and not another, the same cake recipe may behave differently.
Can you freeze raw courgette instead?
Many people put raw courgette into a freezer bag after slicing it. It may remain usable for certain cooked dishes, but the NCHFP's tested quality-preserving approach calls for blanching.
Unblanched vegetables can undergo quality changes during storage even at freezing temperatures. For a large harvest, following the recommended method is more dependable than experimenting with every packet.
If you need a quick one-off solution for tomorrow's soup, cooking the courgette into the soup and freezing the finished dish may be simpler than preserving raw slices.
Use frozen slices straight in a cooked dish
Add frozen courgette to soups and stews where the recipe permits. It will release moisture and soften quickly, so you may need less additional liquid than usual.
For roasting, frozen slices are unlikely to brown and hold their shape as well as fresh ones. High moisture makes it difficult to achieve the golden surface you expect from fresh courgette.
For ratatouille or pasta sauce, the softer texture may not matter. You can cook away excess liquid and let the vegetable contribute to the sauce rather than trying to keep every round intact.
How to thaw grated courgette for baking
Put the required portion in a clean covered container in the fridge and allow it to thaw. Drain the released liquid as recommended by your baking recipe.
Don't leave thawed vegetable sitting in a warm kitchen for hours. Once defrosted, handle it as a perishable ingredient and use it promptly.
If you have several recipe-sized packs, thaw only what you need. The point of portioning is to avoid unnecessary waste.
Keep freezer packages in good condition
Use a freezer operating around −18°C and check that bags remain sealed. Exposure to air can cause freezer burn and loss of flavour or texture.
Rotate older packs to the front. A date label is especially useful when one summer's courgette crop overlaps with the next.
If a bag contains heavy ice or the vegetable smells odd when prepared, investigate storage conditions rather than automatically cooking it for longer.
Why frozen courgette sometimes disappoints
Mushy slices often reflect overblanching, slow cooling or the natural softening caused by ice crystals. Use the recommended timing and cool quickly.
Watery grated courgette isn't a failure if you plan to drain it for baking. It becomes a problem only when you add all that liquid to a recipe expecting drained shreds.
Oversized marrow-like fruit gives coarser results than smaller tender courgettes. Pick fruit regularly during the growing season and freeze it while still at its best.
The most useful principle is to match the pack to its purpose: blanched slices for cooked dishes and measured steam-blanched shreds for baking. That turns a glut into meals rather than a drawer of mysterious frozen vegetables.