9

It is widely claimed that cold-press juicing machines are better than the cheaper, and more common, centrifugal juicing machines, because they avoid degrading the nutrients in the juice through oxidising and overheating.

The problem with centrifugal juicers is that the fast-spinning metal blade generates heat, which destroys some of the enzymes in the fruits and vegetables you're juicing. The heat also oxidizes those nutrients, rendering less nutritious juice than a cold-press juicer.

It’s been proven that heat damages the vital enzymes and nutrients that we are trying to extract from the juice in the first place. The Norwalk is different from centrifuge juicers because there is no spinning blade that is rotating at extremely high RPMs causing initial friction, heat and oxidation, all in which lead to a lower nutrient content. Juices that are made from a Norwalk get upwards of 5 days shelf life with minimal nutrient degradation, compared to a centrifuge that encourages consumption within the first 4-6 hours.

Traditional juicers, or centrifugal models, use fast-spinning blades to tear apart produce, but the process adds some heat and exposes ingredients to air, two things that cut down on how many nutrients make their way into your glass.

Is there evidence that juice from traditional juicers has less nutrients than juice from cold-press machines?

6

Short version: Maybe, but the scientific literature is really bad for this. It also seems to depend on how long it takes to extract juice from a certain amount of fruit. The longer it takes, the more likely it has some impact.

Long version:

First, do different juicing methods affect anything about the juice they produce? There doesn't seem to be a literature on the effects of different juicers on nutrient content, but there is a modest one on the effect on flavours, juice yield, and amount of particulate in the juice. The main difference seems to be that cold pressing ends up extracting juice from only the flesh of the fruits, while "hot pressing + maceration" (which is an industrial process that seems similar to a blender or centrifugal method) extracts from seeds and/or skins as well. If there are nutrients that break down when heated, and are present in the flesh of the fruit, it stands to reason that cold pressing would recover them better. This paper has a good discussion of the effects in grapes, but doesn't address nutrition explicitly, only certain oils that affect the flavour.

This rather interesting book covers (starting around page 50), the different things that can affect flavour, colour, clarity, etc. of juice at small and medium production scales. Using a hot press (where the fruits are heated to ~60 degrees and possibly macerated before juicing) does have some effects.

Okay, so what sorts of nutrients might break down during hot pressing? This paper shows that at least vitamin C (which is presumably a nutrient of interest in juicing) is prone to degradation at the temperature range used in hot pressing (~60 C). However, they exposed broccoli to 60 C temperatures for 10 minutes continuously to get that kind of effect, so it's unclear whether exposure during juicing would be long enough.

Can a home juicer get that hot? While, a centrifugal juicer is basically a blender. I could not find any good information on the temperatures they reach (just a lot of unsourced health websites). However, there are definitely higher end blenders capable of bringing their contents to boiling or near boiling temperatures. This Cooking SE question covers how to make soup using only a blender (heat by running on high), and this blender website advertises that you may be able to boil soups in some of its models. It stands to reason then that a lower-end blender should also heat its contents, even if it doesn't go quite as fast. Since it only needs to get up to 50 or 60 C to damage e.g. vitamin C, it might be able to do that.

However, this paper, appears to show that pomegranates juiced via blender actually yield more citric acid than those juiced by press (tables 1b and 1c). While citric acid is not a nutrient, this shows that some compounds are better extracted via blender than press, so even if say, vitamin C, extraction were reduced, some other nutrients might be present in higher amounts (maybe essential oils from the seeds?).

So overall, what can be said is that:

  1. There doesn't seem to be a real, public, study that looks at these effects directly. The juicing industry (and therefore juice science) is very concerned about how your juice looks, tastes, and smells, but doesn't seem to care about whether its nutrition is affected by the extraction method.

  2. There is a plausible mechanism of action for a centrifugal juicer to degrade nutrients: spinning stuff fast and hitting it over and over makes it hot, and hot stuff tends to degrade certain types of nutrients (though if it gets too hot, the nutrients can become stable again).

  3. There is also a plausible mechanism of action for a centrifugal juicer to get more nutrients: spinning stuff fast and hitting it over and over can extract things from more parts of the fruit than cold pressing it can.

Just a maybe. It does seem like in general, cold pressed juice has better "flavour" properties, but hot pressing yields more actual juice though. So maybe that can help you decide what to buy.

  • This got me thinking and I asked a question on Physics SE about how much the juice will be heated: physics.stackexchange.com/questions/191406/… From my amateurish calculation it seems to be about 6C but I wouldn't yet use it as an argument. – Maurycy Jun 26 '15 at 6:28
  • @MaurycyZarzycki That question and the accompanying calculation make sense to me. The recipes for making soup in a blender call for ~5 minutes of blending in a 1500 Watt blender. You derive an upper bound for heating speed at 0.1.25 C/(KG*s) for a 500 Watt blender. If we assume heating rate scales directly with power, I get a temperature change of about 100 C in about 5 minutes for a 1500 Watt blender making a litre of soup. So I guess it really comes down to how fast a centrifugal blender extracts juice. If it takes just 5 seconds for 100g, no problem, if it takes 30 seconds, problem. – John Doucette Jun 26 '15 at 21:08

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .