Despite it has existed for over a century, a large number of consumers are still somewhat sceptical towards frozen food. It is a common belief that fresh products are of a higher quality, and especially that they have more vitamins and nutrients compared to those exposed to temperatures lower than -18°C (-0.4°F). In reality, a number of scientific reports have proven that there are no significant differences between fresh and frozen vegetables and fruit, and even hint that a number of greens are stored better when frozen.
Most fruits and vegetables have a water content between 70 and 90%, thus tend to perish quickly once picked: microorganisms use water, sugars, and other substances to feed on and multiply, thus reducing the food’s duration.
Natural decay – a process that begins almost immediately upon picking – also induces the loss of vitamins and other nutrients. A vegetable or fruit on a supermarket shelf or market stall will never have the same nutrient concentration it had when it was freshly picked.
Frozen fruit and vegetables store a greater quantity of nutrients as they undergo freezing almost immediately upon collection. Modern technology allows to freeze them completely in only few minutes, and make it so that they preserve at least as many nutrients as their fresh equivalents.
A study performed by the University of California and published on the British newspaper The Guardian made a comparison between eight fresh and frozen fruits and vegetables (corn, broccoli, spinach, carrots, peas, string beans, strawberries, and blueberries). Testing revealed no significant differences between fresh and frozen in terms of vitamin count or other nutrients. As for corn, string beans, and blueberries, it was recorded that frozen products contained a higher amount of vitamin C.
The same was recorded for one type of vitamin B (riboflavin) in frozen broccoli.
The research group also assessed the effects of freezing on vegetable fibres, and compared mineral levels (magnesium, calcium, zinc, and iron) in fresh and frozen goods. Once again, no significant differences were reported, as a further confirmation of the fact that freezing maintains nutrient content for the most part unaltered.
Deep-freezing has been an important step in food preservation systems, but has only been made possible in the first half of the 1900s, thanks to the evolution in technology and consequent creation of freezers capable of reaching very low temperatures. Before deep-freezing technology, throughout the centuries food was stored using natural freezing processes during the cold season: snow and ice were used to improve the durability of the more perishable goods. Nonetheless, the flaw of such natural systems was that they froze the food slowly, leading to the formation of large ice crystals that damaged its cells, thus changing its composition once defrosted.
A new system was required.
The modern deep-freezing technique is attributed to US inventor Clarence Birdseye. Birdseye sensed that foodstuffs needed to be frozen as quickly as possible, both for production quality purposes and for a better preservation. In simple terms, deep-freezing allows to freeze food very quickly, avoiding the formation of ice crystals damaging its tissue. Starting from the late 1920s, Birdseye patented solutions to create more powerful freezers, capable of reaching lower temperatures and making deep-freezing possible. Since then, freezing technology has improved even further, and today it allows the preservation of fresh and pre-cooked food for months, or in some cases years.