We are all struggling with how best to nourish ourselves with fresh fruits and vegetables in this time of Covid-19. Incorporating more of a plant-rich diet will help boost our immune system, which is important for maintaining better health. However, with infrequent grocery shopping, a desire to eat more fresh produce while also minimizing food waste becomes a conundrum. I reached out to registered dietitians Dahlia and James Marin for some advice. I was interested to learn more about freezing produce and how best to do it. –Jeanne What vegetables can we freeze? The majority of vegetables can be frozen, including asparagus, beets, cucumbers, celery, garlic, cucumber, cauliflower, zucchini and other summer squash, broccoli, dark leafy greens (spinach, kale, bok choy, Swiss chard), sprouts (although freezing decreases the bioavailability of nutrients in sprouts), peas, mushrooms, eggplant, onion, okra and winter squash. Vegetables that may not freeze well include leafy greens with a high water content. They are best eaten raw. Also, vegetables that are high in sulfur (e.g., lettuce, endive, cabbage, turnips and radishes) are not good candidates for freezing as they may take on an oxidized, bitter flavor. Should we wash them first? Cut them into small pieces first or, for example, put a whole bell pepper in the freezer? Vegetables should be washed first and, preferably, cut to facilitate ease in cooking later on. Consider the dish in which you’d be most likely to add the vegetables prior to chopping so you can decide if you would like them cubed, cut into strips, shredded, spiralized or riced. Steam them first? If one is dealing with gut issues, we do recommend first steaming then freezing vegetables, as this breaks down their fiber in two ways, making them even more digestible. If gut issues are not an issue, steaming is not necessary. Blanching (quickly dipping the vegetable into boiling water, then running under cold water or dipping into an ice bath), however, may enhance the vegetable’s texture because the process further breaks down the enzymes and gasses present in vegetables that cause the natural ripening process.
What container do you recommend using for freezing? Plastic bags? Pyrex? We recommend freezing produce in glass containers such as Pyrex, Tupperware or Mason jars, or in compostable vegetable fiber baggies or BPA-free silicone reusable bags. These options limit the vegetable’s exposure to bisphenol alanine (BPA) and other potentially endocrine-disrupting chemicals found in plastics. Let’s talk about herbs. Does freezing work for all herbs? Which herbs does it work best for? Which ones shouldn’t you freeze? Are there any special considerations we should take with herbs? Most herbs can be washed and then frozen in a variety of ways, with minimal loss of flavor and nutrients. Left on the stem, hardier herbs like rosemary, dill, thyme or bay leaves can be spread in a single layer on a baking sheet or plate and placed in the freezer. Once frozen, transfer the herb into any airtight container for freezer storage without clumping. To use, simply remove herbs one sprig at a time. Some herbs, like chives, can be chopped and frozen bare, with little loss of flavor.
Flat-leaf herbs like Italian parsley or sage can be compressed and rolled for space-efficient storage. Simply remove stems and loosely fill a bag with the leaves. Tightly compress the leaves into the bottom of the bag, seal and roll the bag around the bundled herbs. Secure with rubber bands or twine and place in the freezer. Rolled herbs can then be sliced as needed for use in recipes. Basil and cilantro can both be de-stemmed, laid flat on a clean, damp paper towel, rolled up and stored.
Do you have any additional suggestions on how best to store and then use these herbs? Like other vegetables, herbs can be stored in glass Tupperware, Mason jars, compostable vegetable fiber bags or BPA free silicone reusable bags. They can also be put into ice cube trays with a bit of water or cold-pressed extra virgin olive oil so they can be used as a base for soups, sautés and bakes. Please discuss how the nutrient profiles change when fruits and vegetables are frozen.
Food scientists at the University of California, Davis designed a study in 2014 to compare the nutritional value of fresh and frozen produce. They measured the nutrients in eight different fresh and frozen fruits and vegetables, including carrots, broccoli, spinach, peas and berries. The conclusion? “Overall, the vitamin content of the frozen commodities was comparable to, and occasionally higher than, that of their fresh counterparts. β-Carotene (a vitamin A pre-cursor), however, was found to decrease drastically in some commodities” (Bouzari et al.). A majority of nutrients are preserved when freezing, with the exception of vitamin A, vitamin D and some antioxidants.
Can you review the concept of how the process of freezing vegetables paves the way for a slight break in the cellulose fiber, thus making vegetables more digestible for some people?
When ice crystals form from water that has expanded in frozen fruits and vegetables, it causes a mild break in the cellulose fiber, making the fiber more manageable to break down and digest. This is why frozen and thawed produce is much softer than before it was frozen.
Do you have any kitchen hacks you can recommend when freezing produce?
Keep a bag or Tupperware in the freezer for vegetable scraps to later use to make vegetable broth. Keep stems of produce such as kale or Swiss chard to add to sautés or soups that will be pureed.
Keep vegetables that appear to be going bad soon in a visible place in the refrigerator. If you know you won’t use them before they spoil, cut them into pieces and freeze them.
When you place them in the freezer, label the containers with the date they were stored so you can quickly identify what was frozen and when it may no longer be as nutrient-dense. Nutrient density loss varies but generally occurs between three and twelve months. Frozen food will keep for at least three months in a standard home freezer before starting to show signs of freezer burn. If you pull something out of the freezer that’s older than three months and it doesn’t show signs of freezer burn, it’s probably still good to eat.
How the food was packaged, how often you opened the freezer (which quickens freezer burn) and where in the freezer the food is stored can extend the “shelf life” of your frozen food. For extended life, frozen produce should be stored in a deep freezer, if available, or in the back of the freezer. Avoid storing frozen produce in the freezer door, which is exposed to elevated temperatures more often. To stretch the shelf-life further, ensure the freezer temperature remains at a consistent 0 degrees Fahrenheit.
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References
Bansal, et al. “In utero Bisphenol A Exposure Is Linked with Sex-Specific Changes in the Transcriptome and Methylome of Human Amniocytes.” Journal of Clinical Endocrinology & Metabolism. 19 Sept 2019. doi:10.1210/clinem/dgz037
Bouzari, et. al “Vitamin retention in eight fruits and vegetables: a comparison of refrigerated and frozen storage.” Journal of Agricultural and Food Chemistry. 13 Jan 2015. 63, 3, 957-962. 2014
HGTV. “Four ways to freeze fresh herbs.” 2019. www.hgtv.com/outdoors/gardens/garden-to-table/4-ways-to-freeze-fresh-herbs
The National Center for Home Food Preservation. “How Do I? … Freeze.” 2017. nchfp.uga.edu/how/freeze.html
Rubin, et. al. “Bisphenol A: an endocrine disruptor with widespread exposure and multiple effects.” Journal of Steroid Biochemistry and Molecular Biology. Oct. 2011. doi:10.1016/j.jsbmb.2011.05.002
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