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Aldi Australia, a supermarket, recently stocked a vacuum blender - an appliance which blends food under lower pressure.

On the packaging, there are a number of claims about the benefits of vacuum blending:

Why vacuum blending?

  • Preserves nutrients
  • Lower foam and froth
  • Fresh flavour for longer

Are these claims valid?

picture of vacuum blender box

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user1605665
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    Claim 1) and 3) are generic to vacuum packaging of foodstuffs, and should be comparatively easy to source. Only 2) is specific to a vacuum *blender*. – DevSolar Jan 13 '20 at 09:53
  • @Devsolar: I've never used such a device, but I don't think it packages the result into a vacuum. Another source of [similar claims](https://www.ukjuicers.com/info/vacuum-blenders-vs-traditional-blenders-a635) suggests that, by mixing less air into the fluids, there is less exposure to oxygen. even if it is stored in a normal jug. This seems the claim to be tested. – Oddthinking Jan 13 '20 at 10:01
  • @Oddthinking: Whether you package something in vacuum or blend it in vacuum, the mode of effect is the same -- less exposure to oxygen. The difference would be gradual. As I said, the only thing that would have to be answered for a vacuum *blender*, specifically, is "lower foam and froth". – DevSolar Jan 13 '20 at 10:56
  • The "less foam" part doesn't seem to me like a plus. Several recipes actively use the air mixed in from a blender to give the dish it's target properties - homemade ice cream being the first one that comes to mind. – T. Sar Jan 13 '20 at 10:56
  • @T.Sar-ReinstateMonica yes, but largely irrelevant to the use of this specific device which seems to be to create fruit juices. It doesn't seem to claim that the resulting product tastes the same or better, only that it's implied to be "healthier". – jwenting Jan 13 '20 at 10:59
  • @DevSolar: I suspect we are agreeing, but let me check. If someone said: "Here is a journal article that shows apple slices stored in a vacuum packed bag takes longer to turn brown than apple slices stored in a regular plastic bag. Therefore, blended apple juice, stored in a regular jug in the fridge, will stay fresh longer if it was blended in a vacuum." we would both reject that as a leap too far, right? – Oddthinking Jan 13 '20 at 11:22
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    @Oddthinking: Correct. It would take a) some insight into how oxygen denaturates vitamins and / or other nutritients and degrades flavor, and b) that blending in a vacuum results in the produce having sufficiently less oxygen mixed into it to make a difference (which sounds similar but is yet distinct from answering 2)). Alternatively, of course, an independent study into vacuum blenders vs. conventional blenders, but I guess that would be harder to come by in a form that properly eliminates other variables... – DevSolar Jan 13 '20 at 11:45
  • For claim 2, "less foam", what should logically happen is that the bubbles should be the same or a similar size, but when the partial vacuum is released they will be smashed down to a smaller size, based on how strong the vacuum was. But I doubt physics-based analysis meets this site's standard of proof. – piojo Jan 15 '20 at 02:38
  • @piojo, rather the opposite. In vacuum, bubbles (of the remaining air already present in the mix) will expand to a much larger size and will rise and "pop" at the surface. Using vacuum is a routine way of degassing mixes such as epoxy or silicone, in order to make uniform bubble-free molds. Initially, when exposed to vacuum, the liquid frothes enormously, and then there is simply no air left in it. – Zeus Nov 17 '21 at 08:30
  • @Zeus Right, I said when the vacuum is released. You're talking about when it is drawn (and bubbles rising and/or popping, which isn't necessarily related to whether bubbles will form). You can see a demonstration here: https://www.youtube.com/watch?v=FrqUrdbMAKA&t=134s – piojo Nov 17 '21 at 11:11

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In short:

  • Most reviewers agree that the smoothies prepared by vacuum blenders are less frothy than those prepared by regular blenders, but they don't necessary agree about the better taste.
  • Immediately after blending, there is a very small loss (<5%) of nutrients, such as vitamin C, prepared by regular blenders; after 1 hour of storage, the loss is still <20% (here). The producers of vacuum blenders tend to present the results of their own studies in a misleading way, like 3 times better preservation of vitamin C after 8 hours (here) and 5 times better preservation after 24 hours (here), compared to regular blenders, but this is not how much a "nutrient-conscious" person likely waits before drinking a smoothie. Vacuum blenders also do not preserve the amount of minerals or macronutrients (carbohydrates, proteins, fats) better than other blenders.

Does vacuum blender cause less foam/froth and taste better?

There are pictures and videos of several fruit/vegetable smoothies with obviously less frothing after vacuum blending. The claim has been also repeated in various reviews.

Consumer Reports:

"In vacuum mode, all four blenders made smoothies that were smoother, less foamy, and more consistent in texture than the smoothies we made in regular mode," says Cindy Fisher, who oversees our blender tests.

In our informal taste test, staffers found that the smoothies were comparable...

In a review by Which.co.uk, they also observed the difference in frothiness but not in taste.

Business Insider:

It makes your juice taste better and last longer.

So, the reviewers agree about less froth, but not necessary about the better taste of smoothies prepared by vacuum blenders.

Does vacuum blender preserve nutrients better than classical blenders?

1) In this video, an apple smoothie made with a vacuum blender remains green, while the one made with a usual blender becomes progressively brown within 10 minutes. The browning is due to oxidation of polyphenols after exposure to air in the same way as in cut apples (Science Focus). From this video alone, it is not possible to quantify the effect: what percent of polyphenols got oxidized and how less nutritious would such a smoothie be.

2) Philips presented the results of "independent research:"

The University of Natural Resources and Life Sciences, Vienna (BOKU) conducted independent research. They found that preservation of nutrients is higher with a high speed vacuum blender compared to normal blending for vitamin C and antioxidants. Up to three times more of vitamin C was persevered after 8 hours vs normal blending and 60% more antioxidant activity preserved after 8 hours.

After 8 hours, the loss of vitamin C in the smoothie made by a normal blender was ~250% greater and the loss of antioxidants ~60% greater than in the one made by a vacuum blender, but they don't say what was the difference after only 1 hour.

In one study with a strawberry juice prepared by a usual blender, less than 20% of vitamin C was lost after 1 hour of storage at 28 °C, but almost 100% after 8 hours (Figures 3 and 4). This clearly suggests that the loss of vitamin C in a smoothie prepared with a usual blender (in the Phillips study mentioned above) would be also much smaller after 1 hour than after 8 hours.

Jan
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    Your references marked 1) and (especially) 2) are on the mark, but they come from biased sources, and we can't check them. Your other references don't seem to be relevant. (e.g. it doesn't look like the strawberries were juiced in a vacuum). – Oddthinking Feb 03 '20 at 22:53
  • The time differential you paint is actually counter intuitive. EG C & B1 will degrade quickly with oxygen present, 'vacuum' blending reduces oxygen exposure in preparation. So, in prep, 'vac' should have the edge, after pouring it's zero-hour again for both, but 'vac' having a head start? Why should longer time make a greater diff like you describe when the effect you present is sth like half-time based? Is there anything besides theory that brings together 2 & 3 (whether vac or not, between 1&8 hrs VitC will be oxidised to ever more degrees)? – LangLаngС Feb 04 '20 at 01:40
  • I'm aware that some sources are biased and that was my point. Presenting a loss of 250% vitamin C after _usual_ blending compared with vacuumed blender is biased to show a much greater loss that occurs within an hour, during which time a smoothie is often actually drunk. So, I mentioned the study with a strawberry juice made by a _usual_ blender, to show that vitamin C loss is much smaller after 1 hour (<20%) than after 8 hours (~100%). This can be directly compared with the part of the Philips study with a smoothie prepared in a _usual_ blender. – Jan Feb 04 '20 at 08:36
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    @LangLangC: The hypothesis behind the claim seems to be that foam has a very large surface area between the air and the liquid. So, even *after being poured*, it has a higher rate of oxidisation, and that differential should continue until the foam finally settles – Oddthinking Feb 04 '20 at 08:52
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    @Jan: OOoh! The strawberry juice was refuting aspects of the Phillips study? That wasn't at all clear to me. – Oddthinking Feb 04 '20 at 08:53
  • The whole idea of nutrient preservation by vacuum blenders is that the vacuum ones mix less air into the smoothie, so the vitamins in it will become less oxidized (degraded). But if you check [this video](https://www.eujuicers.com/magazine/a-whole-new-way-to-blend) (at 1:00), the colors of both smoothies right after blending are very similar and then change (due to oxidation) a lot within 10 minutes. This means that not much oxidation occurs _during_ blending in either blender, but mainly _after_ it and that the bubbles in usual smoothie will result in more oxidation. – Jan Feb 04 '20 at 08:54
  • Yes, exactly, the strawberry study shows how very different is oxidation between 1 and 8 hours. The oxidation in the frothy smoothie will be faster. – Jan Feb 04 '20 at 08:55