Frozen vs. Fresh Vegetables

[Carolyn Tillie]

I got into quite a too-doo with my sister about vegetables.

I tend to eat my vegetables with the season in which they are fresh. So much so that in discussing our T-Day menu, I dismissed her suggestion of frozen peas or lima beans.

She contends that with SOME vegetables, there are actually more minerals, vitamins, and various nutrients in a frozen vegetable as they probably frozen more freshly than I can buy them in a grocery store.

Now I try to buy at Farmer's Markets when I can, but it is now winter and the markets are shut down. We are working on the assumption that the vegetables in the grocery stores could be a week or two or three weeks old.

I think she is nuts - that a fresh vegetable, even one that was harvested and held for some time will still be healthier than any vegetable I could get out of the freezer case.

Scientists, I need you to weigh in, please!

[Squeat Mungry]

I'm no scientist, and I'll look forward to more authoritative responses, but I do remember hearing Sara Moulton say something to the effect of flash-frozen peas usually tasting as fresh or fresher than those you can find in the average supermarket, simply because they are frozen immediately upon being picked. I do know from personal experience that the fresh taste of peas begins to deteriorate extremely rapidly once they have been picked and shelled.

Squeat

[melkor]

It's true that some things are better frozen in season than fresh out of season. Corn for example is awful this time of year - frozen corn is slightly less awful.

Your quite close to dixon - why not just head out to Pedricks and pick up your produce there? They have good stuff year round, and it's often cheaper than the grocery store.

[fifi]

The answer is... it depends.

The results of freezing will differ depending upon the vegetable, how it is handled after picking, and how it is processed prior to freezing.

The condition of fresh vegetables will depend upon the vegetable, how it is handled after picking, and how long it takes to get to you.

Let's just take green peas for instance:

If you walk out in your garden, pick your peas, shell them right away and cook them immediately, you probably can't get any better than that. If your farmer's market farmer picked his peas that morning you are still pretty good. If he has been picking them during the week and storing them properly, maybe not as good as that morning but pretty good. If he didn't store them properly, for instance at the right temperature to slow down the enzymatic processes (whatever that is for a pea), then you might have peas that aren't so good. So you can have a range of quality in the fresh peas.

Now let's look at the frozen peas. We are still talking about the same variables. Typically, blanching prior to freezing is done to "kill off" the enzymes in those vegetables where that is a factor. While freezing slows that activity WAY down it may not stop it altogether. If the processing plant is close to the source of the peas, you are likely to get a good and consistent quality product from the freezer. Probably better than from the farmer at the market if he has not handled his product properly, maybe not better if he did. The frozen peas can be a lot better than the fresh in the supermarket, especially if a lot of shipping time is involved for the fresh.

In the Rio Grande Valley, the processing plants are usually close to the source. I don't know about California and Florida, for instance, but I suspect that the same is true. Also, remember that commercial processing plants have blast freezers that can freeze MUCH faster and to lower temperatures than you can at home. (I have been in those things. They are so cold that they are dangerous. The plants that have them have the same rules that you would have for entering into any other danger zone.)

Different vegetables react differently after picking. Some are more sensitive to storage conditions than others depending upon whether you are looking at sugar to starch conversion (sweet corn), vice versa (potatoes stored too cold) or other nutitional degradation.

So... after all of that blather... there is no yes/no answer. Sorry.

[CheNiPenso]

Is fresh healthier than frozen? Sure, if you pick it yourself and cook it immediately. But the second many vegetables (especially corn and peas) go off their vine/stalk, they begin to degrade. Flash freezing preserves the vegetables within minutes of harvest. This is not to be confused with canning, wherein the cooking process can damage the nutritional content of the food.

I definitely think that, in some cases, frozen outperforms fresh even in season. For those of us in cities, where the produce has to travel hefty distances and often through significant climatic changes to get to market, corn and peas are pretty much always best from the freezer section. (Frankly, I have yet to have an ear of corn since I've lived in San Francisco that does not taste like cardboard, it degrades in flavor so quickly.)

[Nick]

Commercial pea freezing in England.

Awhile back I read that in the US some companies are actually freezing peas in the field rather than trucking them. Don't know if that's true. I do know that I shucked (and ate) a lot of peas from the garden when I was a kid. Pick and shuck them just before cooking for supper, pick and shuck just before blanching if they were going into the freezer. My mother loved peas and we'd freeze enough to have them at least once a week if not twice during the winter. Guess I had my fill from back then. I might have eaten green peas twice in the last ten or fifteen years.

Edit: My mother insisted on picking and shucking corn when the pot had been put on the stove.

Edited November 25, 2003 by Nick (log)

[badthings]

Fifi (or other scientist): I thought that the ice crystals in food that has been frozen ruptured cell walls (thus causing the thaw puddle). Are there significant amounts of anything besides water in those puddles? Like volatiles or water-soluble vitamins?

Frozen peas can be surprisingly good in terms of texture/flavor.

[fifi]

Again... It depends, usually on the vegetable and its particular cell structure. Peas freeze quite well. Spinach will always wilt. Yes, the puddles can contain some of the water soluble nutrients. The other factor is that blast freezer. The freezing is so rapid that large ice crystals don't have much of a chance to form. So, even spinach frozen in a blast freezer will have less leakage than if you freeze it in your home freezer.

[badthings]

Just how cold are those blast freezers? I want one.

I did a little research:

Favell DJ, "A comparison of the vitamin C content of fresh and frozen vegetables," FOOD CHEMISTRY 62 (1): 59-64 MAY 1998

Abstract:

This study, using vitamin C (ascorbic acid) as 'marker', allowed a direct comparison of the nutritional quality of fresh vegetables at various stages of distribution and storage, with the same vegetable commercially quick-frozen and stored deep frozen for up to 12 months. The nutrient status of frozen peas and broccoli was similar to that of the typical market-purchased vegetable and was superior to peas that have been stored in-home for several days. Fresh peas and broccoli retained their quality for up to 14 days when stored under chill conditions. The nutrient status of frozen whole green beans and frozen carrots, with no loss on freezing, was similar to the fresh vegetable at harvest. Frozen spinach also compared reasonably well with the harvested fresh vegetable and was clearly superior to all market produce.

"Market produce" was defined as stored at 20º C ("ambient"), or refrigerated at 4º C ("chill"). "Frozen" was held at -20º C. Obviously, none of these correspond perfectly to real-world conditions. For peas, the results, in mg vitamin C/100 g:

garden fresh: 30.9

day 3 ambient: 20.6

day 3-7 ambient: 12.1

day 2/3 chill: 28.8

day 3-7 chill: 27.4

frozen (initial): 19.6

frozen (12 months): 17.2

The other vegetables tested did better.

Although they call it a "marker", vitamin C loss is not connected to any other compound. All losses are attributed to enzymatic oxidation. It seemed odd to me that they made no attempt to quantify losses due to cell rupture from ice crystals, but then I realized: they never thawed the frozen produce. That somwhat limits the usefulness of their results!

Here's another article that is relevant, although it doesn't compare fresh vegetables:

Puuponen-Pimia R, et al., "Blanching and long-term freezing affect various bioactive compounds of vegetables in different ways," JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE 83 (14): 1389-1402 NOV 2003

Abstract:

An extensive study on the effects of blanching/freezing and long-term freezer storage on various bioactive compounds of more than 20 commonly used vegetables was performed. Effects were strongly plant species-dependent. Contents of dietary fibre components either were not affected or increased slightly. Minerals in general were also stable, but some losses of soluble minerals by leaching were observed. Phenolic antioxidants and vitamins were clearly more sensitive. Significant losses (20-30%) of antioxidant activity and total phenolics were detected in many vegetables. A qualitative HPLC profiling method for phenolic antioxidants was developed which proved to be very useful when evaluating the complex behaviour of phenolics during food processing. Up to one-third of vitamin C contents were lost during blanching, and further slight losses were detected during storage. Folic acid turned out to be very sensitive to blanching, with more than half of the vitamin being lost, but was stable during freezer storage. Carotenoids and sterols were not affected by blanching or freezer storage. The usefulness of the applied screening methods for evaluation of the effects of processing on vegetables is shown.

EDIT: and another:

Giannakourou and Taoukis, "Kinetic modelling of vitamin C loss in frozen green vegetables under variable storage conditions," FOOD CHEMISTRY 83 (1): 33-41 OCT 2003

   

Abstract:

A systematic kinetic study Of L-ascorbic acid loss of four green vegetables was conducted in the temperature range of freezing storage. The temperature-dependence of vitamin C loss in the -3 to -20 degreesC range was adequately modelled by the Arrhenius equation and activation energy ranged from 98 to 112 kJ/mol for the four-frozen green vegetables. The developed models were validated in fluctuating time-temperature conditions, in order to establish their applicability in the real marketing path of the commercial products. Based on the models, the nutritional level can be estimated, at any point of the freezing chain, when the full time-temperature history is available. Comparison among different green vegetables showed that the type of plant tissue significantly affects the rate of vitamin C loss. Frozen spinach was found to be the most susceptible to vitamin C degradation, peas and green beans demonstrated a moderate retention, whereas okra exhibited a substantially lower loss rate.

Edited November 25, 2003 by badthings (log)

[Suzanne F]

badthings: The blast freezer end at Dufour was at 0ºF; I'm not sure what the fan speed was. But I never wanted to be in there more than a couple of minutes at a time when pulling ingredients from the locked cage there.

[therdogg]

Nutritionally, frozen can definitely be as good as fresh; and out of season I think it can often taste better too. Strawberries or raspberries, flash-frozen in season, will taste better in baked desserts than the South American "fresh" varieties we get in out supermarkets in November. Depending on where you're from, there might not be a whole lot of fresh veggies in winter other than, say, kale. Since I'm not willing to limit our produce to hearty winter greens and root vegetables (although I'm filled with admiration for those in chilly climes who still eat locally and only in season) I opt for frozen over the less appetizing "fresh" stuff.

[mudbug]

badthings,

You can flash freeze small quantities of fresh produce with dry ice and a cooler.

This was demonstrated by Alton Brown in his "Strawberry Sky" Segment (scroll down to scene five). It's amazing, you can actually flash freeze strawberries using this method, thaw them, and enjoy scrumptious firm strawberries in the middle of winter!

Carolyn,

As mentioned above, it is entirely possible and highly likely that some frozen produce is indeed preserved by methods which preserve nutrients and result in higher nutrition than can be found even at a farmer's market depending on when the produce is harvested and frozen as well as harvested and eaten by a farmer's market or grocery store consumer.

It has been scientifically proven that produce such as corn, blueberries, strawberries, and other produce can definitely have a higher nutritional content when flash frozen within hours after harvest than if they go from your garden to your counter for a couple of days before being eaten. Strawberries for instance, immediately start losing their nutrition minute by minute once picked.

Anyone who has had the opportunity to try fresh corn literally from the stalk and harvested before the silks turn brown will tell you that the flavor and texture can change within half an hour. There's a reason why there are stories of farmers who literally bring the grill into the middle of the cornfield to enjoy the produce at it's peak.

There are plenty of sources and studies available for you to browse.

Here are just a few:

http://www.ext.colostate.edu/pubs/columnnn/nn970122.html

"...they're usually processed immediately after harvest, when nutrient content is at its peak..."

http://busycooks.about.com/library/archive...ozenproduce.htm

"Registered Dietitian Mary Choate writes that fresh fruits and vegetables may spend as much as seven to fourteen days in transit, while produce bound for the factories is processed within 24 hours of being harvested."

http://www.stayinginshape.com/3osfcorp/libv/p19.shtml

"...if you live in an area where fresh produce is shipped long distances or stored for long periods of time before purchase, frozen or canned produce may actually be higher in nutritional content."

http://www.healthyfood.org/sub/news_2.01.01.html

"...frozen vegetables are picked at the peak of freshness, which locks in their nutrients. On the other hand, "fresh" produce has been picked unripe and hard in order to last through shipping..."

http://members.aol.com/rlauera/columns/fresh10.htm

"Light, oxygen, varying temperatures and humidity all affect the freshness of fruits and vegetables and, depending on the produce, can result in lost vitamins and minerals within just a few days..."

http://www.nutritionnewsfocus.com/archive/CookNutAway.html

"...fresh no longer means "just picked." Produce bought in a supermarket is often picked weeks before the consumer gets them..."

So it really depends. Unless you know each source and the history of the harvest and processing, you may never really know for sure unless you yourself grow the produce a few feet from your kitchen door and either pick and eat or harvest and flash freeze.

[Carolyn Tillie]

Mudbug;

Wow.

Thank you!

[Mayhaw Man]

badthings,

You can flash freeze small quantities of fresh produce with dry ice and a cooler.

This was demonstrated by Alton Brown in his "Strawberry Sky" Segment (scroll down to scene five). It's amazing, you can actually flash freeze strawberries using this method, thaw them, and enjoy scrumptious firm strawberries in the middle of winter!

I actually did this thanks to that episode. I am never satisfied with what happens to blueberries after I freeze them and thought this would be fun to try. It worked like a charm. The hardest part was finding carbonic ice. Te rest was a snap and they are pretty much just like fresh when you thaw them out.

[badthings]

More information (from Favell 1998 cited above):

days to frozen value (days from harvest for vit. C to drop to frozen levels, depending on storage temp.):

peas (ambient) <3

peas (chill) 14

broccoli (ambient) <2

broccoli (chill) 18

green beans (ambient) <1

green beans (chill) 1

spinach (ambient) <1

spinach (chill) <2

carrots (ambient) <1

carrots (chill) <1

As noted above, this does not take into account whatever nutrient loss occurs during thawing. It also doesn't take into account the problem of produce picked green to "ripen" during shipping, as mudbug pointed out. Based on this, I would say that many vegetables even "in season" in supermarkets are in fact less fresh than what you'll find in the frozen aisle.

EDIT: Though I see that you are in California too -- surely there is a year-round farmers market somewhere near you? Not that they have peas now, anyway.

Edited November 26, 2003 by badthings (log)

[Rachel Perlow]

I've been wanting to post about frozen Brussels sprouts for a while, this seemed like a good thread to revive. I used to only keep petite peas and green beans in the freezer. They were the only vegetables I thought were as good frozen and prepped fresh myself (actually, you can't really buy petite peas fresh, can you?).

I recently bought some frozen Brussels sprouts* when they went on sale at my local supermarket, and I've fallen in love. Well, as much as you can with a small round vegetable. Jason got me into Brussels sprouts. I assumed I didn't like them, but the truth is, my mother never cooked them, and I bought into the common perception of them as icky. However, lightly steamed or roasted, they are a very delicious green veggie and now we eat them quite frequently.

I guess other people have rediscovered Brussels sprouts as well, as they are getting expensive to buy fresh. In addition, you lose quite a bit of the volume of the vegetable when cleaning them. I'd say at least 20%. You need to peel off the outer leaf, cut the stem, clean off the dirt. In fact, I usually quarter them to make sure the inside isn't rotten.

Well the frozen ones are usually smaller, and smaller veggies are sweeter than larger ones. Plus, you don't have to clean them, you pay for a pound, and that's what you end up cooking. All I do is drizzle on a little olive oil and a sprinkle of salt, toss, and into a hot oven for 10-20 minutes (depending on whatever else you are cooking). You want them just cooked, with a little brown on the edges. Yum. I'm a convert.

* Specifically, the Hanover Premium Petite Brussel Sprouts (IQF in a bag). I haven't tried the store brand yet, I suppose I should.

[ghostrider]

It always cracks me up when I buy a bag of frozen Brussels sprouts & the fine print on the bag actually says: Product of Belgium.

[Dana]

My mom never fixed sprouts either, but I, too am a convert. My husband loves them and I've just recently started fixing them with regularity - even for Christmas dinner. I steam them till done - not al dente, but done- push them to the side of the pan, add a little butter and saute some chopped walnuts for a couple of minutes. Stir the nuts into the sprouts and drizzle the whole thing with some walnut oil. Delish. I've always used fresh, but I'll give the frozen a try. I don't know why they wouldn't be just as good.

Frozen green beans smell like grass to me. I just can't get past the smell.

[NulloModo]

You're supposed to peel off the outter leaves and cut off the stem? Who knew? All I can say is that the outer leaves and stem have tasted pretty good every time I have roasted them.

[Mabelline]

I am a convert to a lot of frozen vegetables. Frozen corn allows me to make 12 quarts of corn relish in the depths of cold weather. I love Brussels sprouts, and they are SO's favorite vegetable, besides cauliflower.

Ghostrider, don't you just picture Brussels full of garden patches with stalks of sprouts everywhere, right next to the hop vines?

[jsolomon]

There are other considerations that people aren't mentioning with regards to fresh/frozen vegetables.

Some vegetables, beets, notoriously, have such a tough cell wall that the beasts need to be cooked for the nutrients to even be biologically available, no matter that cooking also destroys some of the nutrients.

So, as fifi said, there's really not a clear yes/no answer. However, the jury is clear: for proper fresh corn, grow/pick it yourself.

[Mabelline]

Who's talkin' about fresh corn? By the time it's put up with cabbage, onions, red and green peppers, spices and then water-packed, I defy anyone to say they can tell it wasn't fresh. I am talkin' about relish.

[ghostrider]

Ghostrider, don't you just picture Brussels full of garden patches with stalks of sprouts everywhere, right next to the hop vines?

←

Exactly!

They started bringing the stalks into my local farmers' market in the 1980s. I still can't believe I was nearly 40 years old before I knew how those things grew! In spite of the fact that they were a fave vegetable from early childhood. I'd always pictured them growing like tiny cabbages.

[Carolyn Tillie]

I had completely forgotten 'bout this thread! I continue to be amazed and never thanks Badthings for that amazing bit of research.

Contrary to how my first post sounded, I do occasionally buy frozen vegetables (frozen baby onions for stews are way easier than trying to blanch and peel several dozen of them fresh!), but I was terribly curious about the actual science of it.

Seems as though some vegetables fare well going through the frozen process while others do not - that is pretty obvious. But I really do appreciate all the input here!

[M. Lucia]

I have to agree with the peas thing, because of the short life of peas, frozen is usually better. I cannot, however, concur on frozen corn, mainly because it is usually some yellow corn that has lost its sweetness. I buy frozen edamame too.

I think frozen berries can be a good option too because so many of the berries out there now are tough and tasteless.

But as for frozen veggies, I would say pimarily peas, though if you want to get into modes of preservation, I think canned tomatoes are pretty great. I even read once that canning actually boosts nutrients in some foods(?).

Oh yeah, and about brussels; I buy the baby brussel sprouts at the grocery. They are pricy, but they are the best sprouts you ever had.