Proponents of vacuum blending claim that it improves quality by reducing oxidation. Vacuum blenders are not yet widely available in the US, but it appears that they may be coming soon. I rigged up my own vacuum container for a Vitamix, and in this post I will evaluate just how much of a quality boost you can expect from vacuum blending.
When you cut an apple or avocado and don’t eat it right away, oxidation is what causes it to turn brown. Oxygen from the air reacts with the exposed fruit, and some of the reaction products are brown.
Blender blades cut and smash food countless times, making blends especially prone to oxidation. Blenders can also whip small air bubbles into the blends, which further promote oxidation. If you’ve ever saved some of a smoothie for later, and then it tasted bitter or just not as good, it was likely because of oxidation.
In addition to color and taste, oxidation can also decrease nutritional value. Smoothies with fresh produce are full of phytonutrient antioxidants, which many people believe are beneficial. When antioxidants are exposed to oxygen, they react with it and lose their antioxidant activity (that’s basically the definition of an antioxidant). Vacuum blender companies in Japan and Korea report a difference of several fold, but as far as I can tell, they do not say how long after blending they made those measurements.
The idea of sealing food in a vacuum to retain quality goes back to at least the 1940s. Industrial-grade vacuum mixers have been around since at least the 1930s. However, the idea of applying vacuum to home blenders is relatively recent. Japanese company Tescom released the first home vacuum blender in 2013. That model has a relatively modest 290W motor. Since then, multiple Korean companies have jumped on the bandwagon, and have released more powerful models. They are not yet available in the US, but they may be coming later this year (they’ve been demonstrating at US trade shows).
How it works
The design of a vacuum blender is actually not very different from a traditional blender. The additional component is a vacuum pump that connects to an airtight blending container. The pump sucks air out of the blending container, so that it can blend in a low-oxygen environment. That means it’s possible to adapt just about any blender into a vacuum blender.
One precautionary note about making your own modifications: a non-vacuum blending container was probably not tested for operation under vacuum. Most of them are sturdy enough that I don’t think there should be any problems, but keep in mind that any modifications will void the warranty. In principle the vacuum could also damage the bearing seal or suck grease out of it. I did some vacuum tests with just water in my modified Vitamix container to see if any air or material would come from the bearing seal. I didn’t see anything come from the seal, but I’m not making any guarantees.
A note about vacuum
Not all vacuums are created equal. It is impossible to create a complete vacuum, so every vacuum chamber gets to somewhere on the continuum between slightly below atmospheric pressure, and slightly above complete vacuum. I mention this because the blending results may vary with the amount of vacuum applied. The setup I put together removes ~90% of the air from the container.
I compared a variety of vacuum blends to otherwise identical non-vacuum blends. I blended the vacuum one first to avoid giving the non-vacuum one an unfair disadvantage. If you want to see how I sealed my Vitamix container, check out my separate page on making a DIY Vitamix Vacuum Blender.
Blended apple yields the most dramatic visual difference I’ve seen in vacuum blending. Initially it looks the same, but over the course of a few minutes the non-vacuum blend turns completely brown. This is an equal amount of cored Granny Smith apple and water, blended 60 sec on high right away:
I also blended just tomatoes (40 sec on high):
In both the tomato and orange blends, you can see that the non-vacuum blend is lighter, and the vacuum blend is a more vibrant color. This is because of tiny air bubbles mixed in to the non-vacuum blends. I’ve seen this more vibrant color in a variety of other smoothies as well. Unlike the apple blends, the tomato and orange blends did not noticeably change color over time.
There were detectable differences in the taste of all of the above blends. In each case, the vacuum blend tasted fresher and more like the item being blended. It was possible to taste subtle differences right away, and over the course of minutes the differences increased.
I think the best description of the apple blends is the difference between fresh and cooked apple. The non-vacuum blended apple didn’t taste awful, but it it was quite different from the vacuum blend.
The non-vacuum blended tomato lost its tomato flavor, and was bland and unappetizing. The vacuum blended tomato tasted like eating a piece of the tomato.
The orange had the biggest difference in taste. The non-vacuum blended orange turned bitter, while the vacuum blended orange kept its pleasant orange flavor.
I also blended some mixed smoothies, but I did not always notice a difference in flavor. A vacuum-blended pineapple berry smoothie and various ginger and lemon green smoothies tasted the same as their non-vacuum blended counterparts.
For the apple and tomato blends above I weighed them to make sure the amount was the same. Particularly with the tomato, you can see that the vacuum blend is a smaller volume, and that’s because of air bubbles mixed into the non-vacuum blends.
I also took a photo of one of my foamiest recipes, this spicy green juice:
There was a noticeable difference in consistency between vacuum and non-vacuum blends, but I think it was mainly due to the air bubbles in non-vacuum blends. However, the non-vacuum blended apple did seem noticeably pulpier.
If you leave a non-vacuum blend for a while, it can start to separate. I believe this is primarily caused by air bubbles sticking to bits of fiber and slowly rising. Vacuum blending prevents separation. Here’s a photo of the tomato blends after 25 minutes:
The first takeaway from these tests is, yes, vacuum blending can have a real impact on improving blends. That said, I don’t think that we need to start vacuum blending everything. It has the biggest impact if you are not consuming the blends right away.
There are other ways you can reduce oxidation:
- Temperature: add ice or frozen ingredients to keep blends cold
- Time: minimize blending time, and consume right away
- pH: lowering pH with acids greatly slows enzymatic oxidation1 (adding lemon or lime is the most common way of doing this)
- Antioxidant: add extra antioxidant (most common is vitamin C)
- Avoid oranges if it won’t be consumed right away
- Bubble removal trick
There are also a few disadvantages to vacuum blending:
- Extra time: pumping out the container takes at least 30–90 seconds.
- Less convenient to adjust recipes on the fly
- Can’t use tamper
This is a big topic, and I haven’t been able to cover all of it here. If there are aspects that you are still wondering about, please let me know, and I can either expand this post or make a new one.
1. Plants contain enzymes that can greatly speed up oxidation reactions. The most common is polyphenol oxidase (PPO). PPO activity is much lower at acidic pH values. PPO also causes polymerization reactions, which may be responsible for the pulpier texture of the non-vacuum blended apple.