AY Honors/Food - Freezing/Answer Key

1. Define the following terms:

a. Blanching: Blanching is a food preparation process wherein the food substance, usually a vegetable or fruit, is plunged into boiling water, removed after a brief, timed interval and finally plunged into iced water or placed under cold running water (shocked) to halt the cooking process. It is best to place the food in a wire basket so that it can be lowered into boiling water, lifted out, and then lowered into the cold water. This is easier than pouring off the boiling water or wasting time trying to fish the food out of a pot of boiling of water. Furthermore, this will allow you to reuse the boiling water for the next batch without having to wait for it to reheat.

b. Quick freeze: Quick freezing is used to quickly freeze perishable food items. In this case, water contained inside the food items is subjected to temperatures well below its melting/freezing point 0°C. This causes the water inside the foods to freeze in a very short period of time.

c. Freezer burn: Freezer burn is a condition that occurs when frozen food has been damaged by ice crystals, due to air reaching the food. It is generally caused by non-airtight packaging. Freezer burn often results in change of texture and discoloration of the affected food. It appears as grayish to brown leathery spots on the food. Although freezer burn affects the quality of food, it does not make it unsafe or unhealthful to eat.

2. What kinds of containers can be used for freezing foods?

Plastic containers work the best. Metal containers also work well. The important considerations are that the container be food-safe, air-tight, and not be damaged by freezing.

3. What are the essential things to be considered when selecting vegetables or fruits for freezing?

First check the quality as you would for any fresh fruit or vegetable. Wash thoroughly and make sure the fruit or vegetable has no salt on it. When you freeze the fruit or vegetable make sure that it is not bumped or otherwise damaged.

4. How do you thaw frozen vegetables for the table? How do you thaw frozen fruits for the table?

Vegetables

Most vegetables should be cooked without thawing first. Corn on the cob should be partially thawed before cooking, and leafy green vegetables should be completely thawed. Thawing should not be done at room temperature. Food is safe indefinitely while it is frozen, but as soon as the temperature rises above 4°C, it is susceptible to bacteria (which can cause food poisoning). Instead, thaw it in the refrigerator 6-8 hours ahead of time, or under cold (below 21°C) running water for 30 minutes. Do not remove the vegetables from their packaging, as this allows bacteria to get in. Turn the package every few minutes.

Drop frozen vegetables in boiling water, and quickly return the water to a boil. Pry the vegetables apart as it thaws so that it can cook evenly.

Fruits

Do not thaw fruit at room temperature, for the same reasons you do not thaw vegetables at room temperature. Instead, thaw fruit in the refrigerator 6-8 hours ahead of time. If you are in a hurry, you can also thaw fruit by running cold water over it, as long as the water temperature is below 21°C, turning the package every few minutes or so. This will take about half an hour for one pound of fruit. If you are going to use the fruit right away, you can thaw it in a microwave oven at a low setting. Do not thaw the fruit completely, as the ice crystals will give it a bit of firmness that freezing takes away.

5. Freeze two vegetables (corn and another of your choice), then prepare and serve for sampling.

Vegetables must be blanched before they are frozen. To blanch, drop the vegetable in boiling water for the "blanching time", then transfer to cold water. When packing into containers, always leave a bit of headspace. Water expands as it freezes, so you must leave room for this expansion or the container will be forced open and the food will get freezer-burned.

When freezing any food, do not fill the freezer with too much warm food at a time and do not stack the packages until they are completely frozen. If you fill the freezer with a lot of warm food all at once, it will take longer for it to freeze which will make for a lower-quality end product. Ideally, you want the food to freeze as quickly as possible. Once it is frozen, you can stack it however you want.

If you have two freezers (say a chest freezer and a refrigerator/freezer), it would be a good idea to lower the temperature of the fridge-freezer to its minimum. Then use this freezer to initially freeze the food. Once the food is completely frozen, transfer it to the chest freezer (at normal temperature) for storage. When you are finished freezing the food, you can raise the fridge-freezer back to its normal setting.

Be sure to label the food packages as you freeze them. It can be difficult to tell them apart later (pumpkin does not go so well in a peach cobbler).

Corn

For corn on the cob, blanch for seven minutes. For kernel corn, blanch for four minutes. Allow it to cool completely. For kernel corn, cut it from the cob leaving one third of the kernel on the cob. Package in freezer bags and place it in a freezer.

Carrots

Cut off the tops and wash. Freeze small carrots whole, but cut large carrots into thin slices or into 1.5cm cubes. Blanch small whole carrots for 5 minutes, and blanch sliced or cubed carrots for 2 minutes. Drain and package into freezer bags, then freeze.

Okra

Blanch small pods for 3 minutes, large pods for 4. Slice into "coins", package, and freeze.

Pumpkin and Winter Squash

Cook in boiling water until the pulp is soft. Remove the rind and mash the pulp. To cool, place the container of pumpkin pulp in cold water. Package and freeze.

Summer Squash and Zucchini

Cut into 1.25cm slices, and blanch for 3 minutes. Package and freeze.

6. Quick freeze a vegetable for easy pouring.

Blanch the vegetables as in the previous requirement. When you are ready to freeze them, place them on a tray in a single layer and separate them so they do not touch one another. After the vegetables are frozen, place them in a container, seal, label, and return to the freezer. The vegetables will separate easily and can be poured right out of the package when you need them.

7. Why is salt not put in vegetables to be frozen?

Salt lowers the freezing point of water from its normal temperature of 0°C to -21°C. Most food freezers operate at -18°C, which is higher than the freezing point of salt water. If food to be frozen contains enough salt, it will not freeze in a regular freezer. If it contains only a little salt, the freezing point will be lowered, but not by as much. Even a small amount of salt will prevent it from quick-freezing.

8. Freeze some peaches in light syrup and also some in orange or pineapple juice. What is the reason for using ascorbic acid in the syrup and not in the fruit juice? Why is ascorbic acid used in freezing peaches?

Packed in syrup

First, you'll need to make the syrup which is just sugar and water. For peaches, you will need a 40% syrup, which is made by dissolving 250ml of syrup in 1000ml of lukewarm water. Chill the syrup before using.

Wash and peel the peaches. Add 2.5ml of ascorbic acid to the syrup. Place the peaches in a container and cover completely with the syrup, leaving some headroom. Wad up some wax paper and place it on top of the peaches to keep them submerged. Seal and freeze.

Packed in Fruit Juice

Wash and peel the peaches. Place the peaches in a container and cover completely with the fruit juice, leaving some headroom. Wad up some wax paper and place it on top of the peaches to keep them submerged. Seal and freeze. Acsorbic acid is not needed when packing in fruit juice because the fruit juice has acsorbic acid in it already. The acsorbic acid will prevent the peaches from turning brown.

9. Freeze one type of berry without added sweeteners.

Wash and drain the berries (except for blueberries which should not be washed). Pack them into containers leaving some headspace, and freeze.

10. Make one kind of freezer jam.

Wash 500ml of strawberries or blackberries, being sure to select only fully ripened ones. Remove any caps and stems, and crush the berries. If desired, you can squeeze blackberries through a sieve to remove any seeds. Put the berries in a large bowl, add 1000ml of sugar, mix well, and let sit for 20 minutes. Dissolve one package of powdered pectin in 250ml of water and boil for one minute. Stir the water/pectin into the berries and sugar for two minutes. Then ladle into containers and freeze.

References

Wikipedia articles

http://www.uga.edu/nchfp/index.html