Friday 22 February 2008


Like many raw fooders, I have enjoyed on occasions a little 'raw ice-cream' (using a frozen-banana base). I've also been sampling lately frozen (and freeze-dried) durian. I've been telling myself that, whilst freezing might affect the enzymes and nutrients in food a little, it doesn't nearly as much as cooking, and, after all, freezing has been used as a method of food preservation for thousands of years. But, then, people have cooked food for thousands of years, and I've always resisted the notion that just because 'everyone' has done something 'for ever' it's gotta be the right thing to do... So, I thought I'd find out a little bit more about the effects of freezing on food.

Firstly, needs to be said that frozen vegetables on sale in shops will have been 'blanched' before freezing. Blanching is cooking food for a short while in boiling water and one reason it is carried out is to 'neutralise' enzymes to maximise shelf life. So, as raw fooders take care to preserve the enzymes in food to minimise the burden on our own digestive enzymes, we won't be buying supermarket frozen veg (note that some juice and smoothie bars use frozen fruit, although fruitarian Anne Osborne has contacted companies selling frozen fruit, and it would seem that frozen fruit is seldom blanched).

But what about foods we've frozen ourselves, without blanching, then dethawed? To what extent is freezing a method of food preservation? Is everything preserved?

My son Joe, in his first week of a BSc in Nutrition, learned that 'when food or solution is frozen, only the water molecules turn to ice and anything else is trapped in vacuoles - in effect dehydrating the food and often denaturing the cells in the food.' 'Denaturing' means changing the properties of the food. For example, when amino-acids (from which we make protein) are changed they can be less easily assimilated by our bodies.
So, freezing does change our food.

Susan Schenk ('Live Food Factor') describes the freezing process thus: 'Unlike most other chemical compounds that contract when they freeze, water expands as it forms ice, and the tiny ice crystals in all cells that contain water are like little bombs going off inside the food. These destroy enzymes, vitamins and all sorts of other molecules.' I happen to know Vitamin E is destroyed by frost.
So freezing does destroy some nutrients.

Enzymes are certainly destroyed through freezing, although there is some uncertainty as to how much. I assume the percentage varies by food, and it would also of course be dependent on how long the food has been frozen for (as pre-raw we all understood that frozen foods have a 'freezer life'). David Wolfe says that freezing destroys between 30% and 66% of enzymes. There is no consensus, but the lowest estimate I've seen puts the destruction at 20%.
So freezing destroys a significant percentage of enzymes.

Some believe that nuts and seeds are resistant to freezing. Susan Schenk says: 'nuts, seeds and dehydrated foods are not much damaged by freezing, and their enzymes are not destroyed because they have no water.' Some say that, certainly with nuts and seeds, freezing doesn't destroy enzymes but simply renders them dormant, and offer as proof for this the fact that nuts and seeds will sprout after freezing. And we all know that seeds can survive a harsh winter and grow into strong plants when the warm weather comes. But, is 'life' in a dark, airless freezer quite the same thing as life outside?

I decided to investigate this further. Firstly, a quick google revealed that nuts do actually contain a little water - they're about 5% water. On this basis I hypothesised that freezing would change and destroy things in nuts and seeds.

Here's how I tested this:

I took two 1/4-cups of wheatberries (wheatseeds). One lot I'd frozen for seven days. The other lot were fresh. I soaked each for 24 hours in same-size containers and same amount of water. I then drained them and left them to sprout.

In each pair of photographs, the berries on the left are the previously-frozen ones.

This is how the wheatberries looked after two days:

Some of the previously-frozen berries had started to sprout. All of the fresh berries had sprouted.
So, even though dethawed, the previously-frozen berries did not sprout as quickly as the frozen, which indicates enzyme activity had been affected.

This is how the wheatberries looked after five days:

The shoots of the previously-frozen are greener than the fresh, and longer. Is that good? Looks as if the previously-frozen are valiantly trying to make up for lost time, and more! But gardeners know that plants that grow quickly initially don't always stand the test of time. What we can definitely say is:
There was a difference in the appearances of the previously-frozen and fresh wheatberries.
I also shook the glasses so that any ungerminated seeds would fall to the bottom.
There were more ungerminated seeds amongst the previously-frozen seeds.
(This leads me to question Susan Schenk's statement that freezing doesn't destroy enzymes in seeds.)

At the five-day point I decided to submit each to a 'taste test'. I tasted the fresh wheatberries. Lovely - sweet. I was just about to taste the previously-frozen wheatberries,
but was put off by the smell!
Please bear in mind I am no Gabriel Cousens and this 'home experiment' would need to be replicated under rigorously-controlled conditions to draw any firm conclusions from it. I simply share my experience with you.

And Marti Fry, Natural Hygienist, in her article 'Does Freezing Harm Foods?' felt that we're OK freezing nuts and seeds as they have 'little water content'. On the other hand, she's not happy with freezing other foods, such as fruit. She summarises the nutritional losses as follows:

1) Cell walls burst and cell contents are spilled due to the internal water expansion; hence the cell's life is lost. When cells burst, certain of their organelles release self-destruct enzymes called lysosomes. While these enzymes are not active during freezing (and some are even destroyed), those which remainintact will speedily decompose the cell contents upon thawing.

2) Oxidation occurs where air reaches the frozen foodstuff; hence nutrients are lost.

She further comments 'Does this mean that banana 'ice cream', fruit smoothies made with frozen bananas, and other frozen foods aren't truly healthful? Well, unfortunately, YES.'

Raw fooders that follow a 'high raw' rather than 100% raw diet may feel just as happy including a little previously-frozen food in their diets as they do cooked food occasionally, and I'd be the first to say this flexibility can make all the difference in being able to stick to a raw food diet (having started out at 75% myself). And, of course, a high-raw diet is still light years healthier than the standard UK diet, with many experiencing big positive health changes on it. But, if you are going to eat food that has been previously frozen, I'd suggest giving it a (sort of) 'pass mark' only if, when dethawed, it looks, smells and tastes just as it did in fresh state and be aware that there is bound to be some nutrient loss.

And those of us who are 100% raw - er - aren't we being just a shade 'inconsistent' if we proudly claim that not a morsel of food heated above 117 F passes our lips (in order to conserve vital enzymes and nutrients) and then tuck into frozen ice-cream or durian. And I will have to say at this point...'oh bother!' (or words to that effect). Thinking about the freeze-dried durian in the cupboard, it does occur to me that, if food is dehydrated before freezing, then there may be no water in it to expand and denature the food? Marti Fry does at least give some comfort here: 'dried foods which are frozen are not harmed because of their extremely small water content: there's not enough water to expand and burst the cell walls.' Good...perhaps I'm OK (!), as long as, of course, the drying temperature doesn't exceed 118 degrees F...:-)


Anonymous said...

I like your article Debbie, and will add your blog to my blog roll!
Are you from Karen Knowler's Raw Food Coach program? I'm looking forward to obtaining my own Raw Food Certification so I can offer raw food classes too!
Take care, ttyl

Debbie Took said...

Many thanks to Hilary Baumann for checking the situation re freeze-drying: 'According to wikipedia the food is frozen at a really low temp and then water evaporated from it.' the food's frozen first then water removed, rather than the way round, as I had thought, looks as if I may have to wave goodbye to the freeze-dried durian if I want to remain 'consistent' (boo-hoo!)

Jen-Jen said...

Wouldn't most durian fruits be irradiated, anyway? They usually require most tropical fruits to be irradiated before they allow them to be imported.

Debbie Took said...

Simple answer is...I don't know. But haven't heard that they are, and think it would be a hot topic on the raw food forums if twas so. If you can get anything firm on this, Jen (inc mangos etc?), please let us know via the Yahoo! Raw Food UK forum.

Springleaf said...

In nature some seeds/nuts, for example, the english horse chestnut tree, MUST be frozen before they will germinate. This prevents the nut from germinating as soon as it falls from the tree in the autum (fall) it must wait untill spring, i.e. after the freezing temps of winter. All seeds of annual plants must do the same. However most winter conditions do not get to -20C (standard freezer temp) or if they do get that cold it is only for a very short time. :-)

Debbie Took said...

Yes, good point, springleaf, and my answer would really be as per your last sentence, ie to what extent is freezing for weeks (or months) in a freezer replicating a 'natural' scenario...I'd be the first to say that something frozen for,eg, one day would be less likely to have enzymes etc damaged than something frozen for months - I reckon the 'does it look, smell and taste the same when dethawed?' is probably still a good policy. Many thanks for commenting, 'springleaf' (after freezing in a UK, or US winter?) and do comment again.

yardsnacker said...

Great article!

bhairava said...

When you heat a molecule, the atoms start vibrating faster, until they break the bond between them. That destroys the molecule. Easy to understand.

However, when you freeze it, the atoms vibrate LESS. How would that exactly destroy the molecule ? It does not.

The changes you see in the frozen food comes from the fact that the cell membrane is broken by the ice crystals that forms - if the "freezing" is fast enough, you can even freeze living organisms and they will live after defreezing.

That kind of "destruction" is on a much bigger scale than the molecular: it's on cellular scale.

Yes, the cell spills its content, and after defreezing the tissue is all a mess - it does not retain its consistency. It's like blending the food, but at the celullar level.

Is the food "changed" ? Of course it is. The same kind of "changing" happens when you simply chew your food.

However, at the molecular level, no destruction occured - it couldn't have. At least I didn't find any reasonable explanation on the net regarding the mechanism by which destruction of the molecules might occur.

Just my 2 cents.

Debbie Took said...

'if the "freezing" is fast enough, you can even freeze living organisms and they will live after defreezing.'

They'll live, sure, as a seed will still be 'alive' in that it will sprout, ie retain its reproductive capacity, but, as shown in the wheatberries example, what then grows is not the same in appearance (and smell) as that which grew from the unfrozen seed.

(I'm coming over all sci-fi-y, thinking of cryogenics...).

Anyhow, many thanks for your contribution, bhairava. Appreciate the information, which I will certainly mull over.

Odile said...

Seems to me that seeds from temperate countries, where things freeze in winter, must be impervious to freezing, or may even need to freeze in order to germinate. That may explain why your previously frozen seeds germinated well and had longer greener stems.

Anonymous said...

My goal is to be 100% raw by the time I turn 50 next month, and ultimately I'd like to cut out all frozen foods as well, but since I can only get whole, frozen (irradiated, sigh)durian here in Oregon (sadly, I've never tasted a fresh durian)that won't be happening ever. I am so hopelessly in love with durian that I'll take it any way I can get it.

Debbie Took said...

Hi durianlover

If it's any comfort, I've had fresh durian and frozen durian, and the frozen durian is a very good second-best. Also, buying fresh durian anyway outside its natural habitats is a bit hit-and-miss. The last durian I bought, from London's Chinatown, wasn't ripe. At least with frozen you'll know it'll be good.

beck said...

that was a very interesting article just what I was looking to find out. Thank you so much for your experiment and information.

Alan said...

Dilute hydrogen peroxide is sometimes used to disinfect sprouts.. I use iodine and potassium iodide in water boiled with a magnesium stick a magnesium hydroxide and hydroxide ions. This works better than hydrogen peroxide, I think; no rotten sprouts.

Debbie Took said...

I have never found it necessary to 'disinfect' sprouts.