Freezing is considered one of the best methods of preserving food. Not only does it increase the shelf life of the product but it also helps to maintain the taste and nutritional value. Freezing does not sterilize the food but stops the growth of microorganisms and slows down the chemical and enzymatic reactions.
Freezing of vegetables has been practiced for a long time. The vegetables which are frozen include corn, peas, broccoli, cauliflower, carrots, beans, etc. The vegetables undergo several processing steps before freezing. The quality of frozen vegetables depends on the quality of the fresh products and how they are handled from the time they are harvested until they are frozen. It is important, to start with high-quality vegetables because freezing will not improve the product’s quality (1).
Advantages of Freezing Vegetables: Frozen vegetables have some advantages over fresh vegetables. Frozen vegetables are available even out of season whereas fresh vegetables are available only during the season. Frozen vegetables have a longer shelf life as compared to the fresh ones. Frozen vegetables can be cooked directly after removing them from the freezer. Now you can even buy fresh vegetables which are cleaned, sliced or diced, washed, etc. before packing and refrigerating. Nowadays due to busy schedules, it takes a lot of time and effort to go to the market and bring vegetables, wash, clean, cut, and then cook. Frozen vegetables are the best option for busy and working populations (2).
Processing of Vegetables before Freezing: Vegetables undergo some processes before being frozen. These steps include raw material receiving, inspection, grading & sorting for size, colour, etc. washing, cleaning, peeling, cutting, blanching, cooling, freezing, and storage. All these steps are important and need to be carried out before freezing vegetables.
Blanching is the most important step that is practiced before freezing almost all vegetables. Blanching is a process of immersing vegetables in boiling hot water for a specific time followed by very quick cooling by placing them in cold/ice water to prevent further cooking. Blanching slows down or stops the enzymatic activity that can cause loss of flavour, colour, and texture of vegetables during freezing. Blanching also reduces the microbial load which helps to increase the shelf life of the vegetables. The time of blanching varies depending on the type of vegetable. Under-blanching stimulates the activity of enzymes whereas over-blanching causes loss of flavour, colour, and nutrients.
There are different types of blanching methods used for blanching vegetables. These methods include water blanching, steam blanching, microwave blanching, etc. After blanching the very next step is cooling by placing the vegetables in cold ice water to stop the cooking process because further cooking can lead to the loss of quality. The vegetables should be thoroughly cooled after the blanching process (3).
Freezing of vegetables: After blanching and cooling, the vegetables are ready to be frozen. Freezing has been successfully employed for the long-term preservation of food providing an extended shelf life to the food products. Natural enzymes present in the food can cause a change in colour, flavour, texture & nutritional value. Freezing slows down the activity of enzymes but does not stop it. It is very important to pack vegetables before freezing. Proper packaging is very important because if not packed properly it can cause vegetables to become dry, hard & tough thereby causing freezer burn. Vegetables should be frozen at a temperature of -18°C or below. Freezing of vegetables should be done quickly after packaging because if there is a delay then the product may lose its quality or eventually get spoiled (4). The types of freezer used to freeze vegetables includes Plate freezer, Air blast tunnel freezer, Fluidized bed freezer, Cryogenic freezer, etc.
The shelf life of frozen vegetables is up to 12 months as per the manufacturer. If stored for a very long time, it can affect the quality of vegetables but it may be safe to consume unless it is spoiled (5).
Drawbacks of Freezing Vegetables: Except for vitamin C and B1, most of the vitamins and minerals are stable during freezing. Some nutrients as well as water-soluble vitamins (Vitamin B and Vitamin C) are lost during the blanching process. Some nutrients found in vegetables are sensitive to heat, due to this the heating of vegetables during blanching can cause some loss of nutrients. Frozen vegetables especially the salad vegetables like tomato, cucumber, etc. may not be as tasty as fresh ones. Actually, items like tomatoes are not possible to freeze, as upon thawing they will totally lose their texture and appearance. It would become mushy.
Freezer burn is another drawback associated with freezing vegetables. It is caused when the product is left in the freezer for a very long time or if it is not packed properly. Due to this, the vegetables become hard, dry, and shriveled and the quality gets deteriorated. Freezer burn can be avoided with the use of proper packaging. The freezer-burned vegetables are still safe to eat unless and until they are spoiled (6).
The demand for frozen food has increased during the past few years. People are skipping onto the products which are easy to prepare and take less time. Due to this, frozen vegetables have become a boon for people with busy schedules. Frozen vegetables are easily available in the market. The use of frozen veggies allows consumers to enjoy nutrient-dense food that is easier to prepare. Customers have a choice of what they want to eat because frozen vegetables are available in a variety of flavours. Due to customers’ busy schedules, there is a considerable opportunity for growth for frozen vegetable products because consumers are looking for quick, easy, and delicious eating options.
- Colorado State University Extension, Established 1908, Freezing Vegetables – 9.330 (https://extension.colostate.edu/topic-areas/nutrition-food-safety-health/freezing-vegetables-9-330/)
- University of Georgia Extension, Reviewed August 2019. Preserving Food: Freezing Vegetables (https://www.fcs.uga.edu/docs/uga_freeze_veg_2019.pdf)
- IOWA State University Extension and Outreach, Freezing: Fruits & Vegetables (https://foodsafety.wisc.edu/assets/PreserveSummer_Freezing.pdf)
A Pacific Northwest Extension Publication, Tonya Johnson and Jeanne Brandt, Freezing Fruits & Vegetables
- Freezer Burn: Why It Happens & Tips to it prevent it, Medically reviewed by Natalie Olsen, R.D., L.D., ACSM EP-C – By Anne Danahy, MS, RDN on February 17, 2020 (https://www.healthline.com/nutrition/freezer-burn)