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The Truth about Heat, Oxidation and Juice Quality
by John Kohler  

One of the questions that we have been getting more frequently is regarding fresh juice quality.  Some say that   heat is created by centrifugal juicers in the process of juicing.

There are several web sites that claim centrifugal juicers and other "high speed" juicers "heat your juice".  Other web sites say that single auger juicers "heat your juice".  Some manufacturers say that heat is bad for your juice. 

Here are a few specific quotes that were copied directly  from various web sites:

  1. The higher RPM's of the centrifugal juicers causes more heat and more oxidation (foaming action) to the food being crushed, which decreases the nutrients in the food.
  2. As the food is pushed through the chute, the slower crushing action of a masticating juicer provides a more effective crushing action than a centrifugal juicer, creating less heat resulting in less damage to the food being crushed.
  3. This process of crushing and squeezing extracts more juice and also has less heat build up than from the high speed at which centrifugal juicers work, which destroys the enzymes and other vital nutrients.
  4. ... It's specially designed to be quiet while at the same time preserving vital nutrients and enzymes often destroyed by friction, heat and oxidation caused by other juicers.
  5. Because Twin Gear juicers operate at a lower speed they also tend to produce less heat.
  6. Centrifugal juicers run at higher speeds and produce more heat than the twin-gear or single auger juicers and introduce more oxygen into the juice.
  7. We are all aware these days that cooking kills essential vitamins and enzymes in food. Are you aware that fast high-speed juice extractors have the same destroying effects, because high speed and friction = heat.
  8. Since there is no heat generated, all of the enzymes are preserved for a fresh and 'live' tasting juice.

These statements would lead a person to believe that certain juicers are really bad, and produce a juice that is no good.   Well read this article to learn the truth.  We don't just tell you, we back up our statements by measuring the temperatures of the juices produced by various juicers.

Who is right, and who is wrong?  Do the web sites have a reason for saying this?  Hopefully this article will dispel those myths once and for all.

First off I would like give you some background information about myself.  

  • I have been juicing for over 25 years. 
  • About 10 years ago, I started juicing almost everyday due to a health crisis.  (Primarily using a centrifugal ejection juicer).   
  • About 7 years ago I started this web site, writing many comparison charts and reviewing juicers.  I use or have used most of the major brand juicers on the market.
  • Several juicer manufacturers value my web site and opinions, that they provide me with prototype juicers before they are released to the public for my evaluation and to get my feedback.

First, we would need to define the nutrients in juice to see if they would be affected by the juicing process.

  • Purified Water
  • Vitamins
  • Minerals
  • Enzymes
  • Phytochemicals including Antioxidants
  • Proteins
  • Carbohydrates
  • Fats
  • Fiber
  • Other Unknown Nutrients

Of all these nutrients, I would be concerned with the loss of Phytochemicals, including Antioxidants and some vitamins. Those are probably the most sensitive nutrients in juice.  

The two main factors that effect juice quality are: Heat and Oxidation.

  • Heat can affect the juice mainly  by causing enzyme deactivation.  Enzyme deactivation  ONLY occurs when temperatures exceed 118 degrees fahrenheit.  In addition to the heat, there is a time component associated with enzyme deactivation.  For example you could probably heat juice to 130 degrees for 1 nano-second with no enzyme deactivation.  Passing your finger over a flame is a similar example. (this is not advised).  
  • Oxidation occurs when you break open cell walls of the produce and expose it to oxygen.  Oxidation occurs when you cut open an apple and it turns brown. In general, oxidation does affect the quality of the juice. Many of the nutrients in the juice are not affected by oxidation, but some are.  Oxidation is a natural process.   Its best  to minimize oxidation.  One way to minimize oxidation is to CONSUME THE JUICE RIGHT AFTER IT IS MADE.  It is true that some juicers minimize the oxidation that occurs while the juice is being created.  The table below shows my ranking of juicers from most to least oxidation created during juicing.  
Most Centrifugal Juicer (omega 1000, Omega 9000,  Acme)
Centrifugal Ejection
(high speed - 8000+ rpm  Breville, Lequip Mini
Centrifugal Ejection
(low speed 3600rpm) - Nutrisource 1000,  Lequip 221
Masticating Juicer - Champion Juicer
Least Single Auger Juicer / Twin Gear Juicer

Oxidation created during the juicing process  is just one factor that should be considered if you own, or are looking to purchase a juicer. Please review this article that talks about selecting a juicer based on your needs.

Ok, enough with all the "small talk". Here is the testing we did with three juicers and measuring the temperature of the juicer blade (or auger), the temperature of carrots before juicing, temperature of the blade (or auger) after juicing, temperature of the pulp after juicing, and temperature of the juice.  You can see for yourself if these various style juicers "HEAT THE JUICE"

HEAT THE JUICE TEST #1

organiccarrots24oz.jpg (40661 bytes)Method: We measured out 24 ounces of baby organic carrots for this test.  We used Earthbound farm baby carrots.  The carrots came out of the same bag, and were of the same batch.  The baby carrots are pre-washed   which greatly reduces preparation time.  The 24 ounces of carrots were fed into each machine and the temperatures were taken.  The temperatures were taken with an infrared thermometer.  The sensor in an IR thermometer collects a small amount of energy radiated from the target, generates an electrical signal that is amplified by a precision amplifier and converted into voltage output, which is then converted into the temperature using a mathematical equation.  Many chefs now use the IR thermometers, since they are non-contact thermometers.   The results are shown below.   The hand grater test was added in at the last minute to show the effects that a standard hand grater would have on a normal size large carrot.  The average temperatures are shown below:

  Lequip Mini 110.5 Omega 8005 Healthy Juicer Electric Hand Grater
Juicer Style Centrifugal Ejection Single Auger Dual Stage Single Auger NA
Temperature of
Blade (or auger) before Juicing
59.9 deg F 59.0 deg F 60.0 deg F 59.3 deg F
Temperature of the Carrots 34.1 deg F 34.1 deg F 34.1 deg F 41.0 deg F
Temperature of the Blade (or auger) after juicing 43.5 deg F 49 deg F 56.4 deg F 53.2 deg F
Temperature of the Carrot Pulp 41.0 deg F 50 deg F 49.0 deg F 50.0 deg F
Temperature of the Juice 46.0 deg F 45 deg F 46.5 deg F NA
Temperature Increase from the carrot to the juice. +11.9 deg F +10.9 deg F +12.4 deg F +9 deg F
Decrease in temperature of blade (or auger) -16.4 deg F -10 deg F -3.6 deg F -6.1 deg F
Overall Yield 12 ounces 13 ounces 9 ounces NA
Comments on Juice Virtually Pulp Free Small Bits of Pulp in Juice Most Pulp left in Juice NA

lequipbladetemp.jpg (50119 bytes)First, you can see that the blade (or auger) of the juicer was warmer than the carrots being put through the juicer. This is because the juicer is at room temperature.  The carrots just came from the fridge.  The difference in the temperature of the blade (or auger) can be explained by the different material the blade (or auger) is manufactured from (metal or plastic) and where it was stored in the kitchen (in a cupboard, or on the counter).

Second, you can see the temperature of the blade after juicing the carrots was LOWER then when we started?  Why is this?  Well, this is due to the fact that the carrots were COLD.  They transferred their "cold" to the blade or auger of the juicer.  The temperature of the blade was  roughly somewhere in the middle.  Some juicers were more effective at lowering the blade temperature, such as the Lequip mini with its stainless steel blade, it really seemed to cause the temperature to drop on the blade.  The drop was not as significant on the other juicers since the augers are primarily made of plastic, which does not transfer cold as well.

pulptemp.jpg (39309 bytes)Third, you see the temperature of the carrot pulp, which is fairly consistent with the temperature of the blade.  With the  exception  of the electric healthy  juicer.  This can possibly be explained by the healthy juicer electric having a plastic auger with metal insert.

 

juicetemppic.jpg (21896 bytes)Fourth, you see the temperature of the juice, which shows that the juice produced by all the juicers were all within 1.5 degrees of each other.  They are all fairly similar.

Finally, you see the overall temperature change from going from the starting product, organic baby carrots, to the end product, organic baby carrot juice.   The Omega 8005 changed the temperature the least by only 10.9 degrees F, followed by the Lequip Mini 110.5, which changed the temperature by 11.9 degrees F.  The Healthy Juicer Electric Changed the temperature the most at 12.4 degrees F.  For fun, to demonstrate the heat transfer, I took a whole carrot, and shredded it against a standard "fine shredder" like you would use if you were shredding carrots over a salad.  That shows the temperature changed a total of 9 degrees.  So the results with using an electric juicing machine is only a few degrees higher. 

HEAT THE JUICE TEST #2

organiccarrots24oz.jpg (40661 bytes)Method: We cut a tray of organic-home-grown wheat grass that friends grew (thanks Rick & Karin).  It was at room temperature.  The wheat grass was grown outside, and not refrigerated.  After cutting the whole tray, it yielded 5.4 ounces of fresh cut wheat grass.  We measured out 2.7 ounces for each juicer.   The Lequip Mini Juicer was not included, since it does not effectively juice wheatgrass.  Wheat grass due to its nature, requires a special wheat grass juicer.  These special juicers are usually a single auger style, or twin gear style.   The same IR thermometer was used as in the first test.  The wheatgrass pulp was fed through back through the juicer about a dozen times to get a higher yield.

  Omega 8005 Healthy Juicer Electric
Temperature of
auger before Juicing
62.0 deg F 63.0 deg F
Temperature of the Wheat Grass 54.3 deg F 54.3 deg F
Temperature of the auger after juicing 84.0 deg F 74.4 deg F
Temperature of the wheat grass pulp 85.4 deg F 74.4 deg F
Temperature of the Wheat grass Juice 62.5 deg F 62.0 deg F
Overall temperature change   from the wheat grass to the juice. +8.2 deg F +7.7 deg F
Increase of Temperature of the Auger +22 deg F +11.4 deg F
Overall Yield of Wheat greass Juice 1.333 ounces .833 ounces

lequipbladetemp.jpg (50119 bytes)This test was more straightforward than the carrot test.  The beginning blade temperature of the Omega 8005 and Healthy Juicer were within 1 degree of each other. 

The temperature of the auger after juicing got a bit warm.   This is primarily because the wheatgrass gets wrapped around the auger, and it rotates against the housing, which causes friction, which then causes heat to develop in the pulp.  The temperature of the pulp then transfers to the auger.  The carrots did not do this, since carrots contain less stringy-fibers so its easier ejected out of the juicer,so less friction occurs.  It would have helped if the wheatgrass was put in the fridge to begin with, so we would be able to get some "coldness" transfer to the auger.

pulptemp.jpg (39309 bytes)In the end, the wheat grass juice was warmer than the starting wheat grass. This was due to the friction caused when juicing the wheatgrass.  This probably would not have been that much of a problem if we fed the wheat grass through the juicer only once.  We took the wheatgrass pulp after it came out of the juicer and fed  it back through the juicer about a half dozen times, to increase  yield.  Each time we did this, it caused the juicer to work harder, causing more friction and heat.    The wheatgrass was diluted with fresh orange/tangerine juice, and enjoyed.

Conclusion:

  • This test shows that all juicers change the temperature of the starting produce.
  • The temperature increase was more when friction was involved.
  • All Centrifugal, Single Auger, Masticating, Twin Gear Juicers produce "fresh, Live, Juice" that contain their full complement of enzymes.

Questions and Answers:

So does juicing "heat" the juice, as some of the web sites would lead you to believe? 
YES, based on the starting temperature of the carrots, and the ending temperature of the juice.  ALL JUICERS change the temperature of the newly created carrot juice.   YES, even twin gear juicers will change the temperature.

Is this a bad thing to increase the temperature of the end product?
I do not think so.  As long as the temperature does not exceed 118 degrees, I feel the extra 10 to 12 degrees is not a problem. Just be sure to start with cold carrots, for best results. There will be minimal (if any) nutritional damage to the juice in my opinion.

Does heat damage the  juice?
I would tend to believe that the extra 10 to 12 degrees that ALL JUICERS produce is not a problem.  What is more of a problem is the OXIDATION that occurs when the juicers rupture the cell walls, which protects the cells from oxidation. 

Does the heat make the nutrition less?
Probably not, unless the heat exceeds 118 degrees.

Do all juicers produce oxidation?
Oxidation occurs with all juicers.  Some juicers create less oxidation in the process of juicing.  (See table above).   Oxidation increases, the longer the juice is sitting around.  So to MINIMIZE oxidation, its more important to DRINK THE JUICE RIGHT AFTER ITS MADE than to worry about, "oh, my centrifugal juicer produces more initial oxidation".  If you cut open an apple, oxidation is created (it turns brown). You never see the browing occur  if you eat the apple as soon as you cut it!

Does the oxidation make the nutrition less?
Yes, oxidation immediately affects the juice. Oxidation created during the juicing process will happen with all juicers.  Here is a question I would ask you:   Is the nutrient value of an apple that has been cut open and left out to "oxidize" for  1 hour much different than an apple that has been allowed to "oxidize" for 1.5 hours?  Probably not much difference. I think many people exaggerate the "damage" done by the oxidation caused by juicers. It's like splitting hairs in my opinion.

Do some juicers produce less oxidation than others?
It is true that different juicers produce less oxidation probably due to the effectiveness of the juicers ability in breaking open the cell wall to release the nutrients inside. That is beyond the scope of this article, but in general, the juicers that produce less oxidation during juicing, are more effective at creating a higher quality juice to begin with.

Is heat or oxidation worse?
In my opinion, oxidation is much worse than 10-15 degree change in the temperature of the produce being juiced.

Do I really need to worry about oxidation and heat in my juice?
I believe manufacturers talk about oxidation and heat to influence your purchase decision.   Hopefully this article will dispel some of those myths.  Heat should not be a factor, since all juicers will raise the temperature of the produce being juiced.   Oxidation plays a role in the quality of juice, this is true.  I would recommend taking the  oxidation factors "lightly".  One could purchase the best juicer that produces the least oxidation, only to have it sit on the counter, and it never being used, since they didn't consider that its one of the hardest juicers to clean.  I have found that if a juicer is hard to clean, it will not get used, then what is the advantage of having "the best" juicer, if its never used?

Are there still benefits of juice made with centrifugal juicers?
I would say there is definitely still benefits from juice created with juicers that create the most oxidation.  There is no doubt about it, drinking  fresh-made juice is better than any PASTEURIZED (cooked), shelf-stable, enzyme-less juice, a soda, coffee or many other beverages the average person consumes.    Remember eating some vegetables is better than eating none at all.  I think this subject is "splitting" hairs for most healthy people, and should not be a major factor for most people.  Of course, if I had a serious medical condition, I would spare no expense, and be sure to give myself every advantage, including purchasing a juicer that would probably create the highest quality juice.

Do any juicers "Cook" Juice?
None of the juicers we sell "cook" juice. There is a juicer called a steam juicer that does "cook" your juice. We do not recommend this type of juicer.   No matter which juicer you purchase from us, be assured, drinking fresh fruit and vegetable juice is an excellent way to include more fresh fruits and vegetables in your diet. Be it least oxidation, or "a little more", fresh juice is STILL GOOD STUFF.  Fresh Juice is better than any store purchased juice, soda, coffee, etc.

What about juices purchased in the store? Are they "cooked"
Juices that you purchase in the store, are most often pasteurized, and are COOKED- to kill the enzymes, so they can have shelf-life.  I would agree these types of juices are not as good as FRESH made juices you make at home with your juicer.

How did this "heat in the juice" thing start?
I have thought long and hard about this one.  I believe that a  manufacturer or retailer  got the context of oxidation created by juicers and heat created by juicers confused.  They published this information online or in brochures, and then other retailers and manufacturers simply copied and added-to the heating the juice myth. This has been taken way out of context in my opinion.    I frequently get people "scared" about the heat or oxidation caused by juicers.  It's nothing to fear or be scared about anymore.  Fresh juice made with your juicer is not worthless.  Hopefully this article shows the truth regarding heat and juice.

How can I increase the quality of juice that I make with my juicer?
There are a few ways I would suggest:

  • Start off with the coldest possible produce- leave the produce in the fridge before juicing. Set your fridge a little colder.
  • Do not overload the juicer.  Feed in only a little produce at a time. Let it work itself out of the juicer before adding more.  Overloading will cause the juicer to work harder, causing excess friction and generating heat.
  • While juicing, occasionally juice a ICE CUBE, which will help to reduce the temperature of the blade/auger and the juice. It will also dilute the juice.
  • Be sure to inspect the cutting blade (on centrifugal juicers) or cutter (on the champion juicer).  Replace if they are dull.  Dull blades do not cut as well, and thus will cause excess friction, which generates heat.
  • Juice in small batches, rather than "juice marathons".   The longer the juicer runs, the warmer things get.
  • You can put your juicing parts (blade or auger) in the fridge,, so they starting  at a low temperature to begin with. (This step is not necessary in my opinion, and may cause premature failure of the juicer parts.)
  • Start off by juicing the highest quality produce available.  In some studies, Organic crops have been shown to be higher in some vitamins, essential minerals and phytonutrients.  
  • If your juicing with a CHAMPION Juicer, chop produce into smaller pieces.  Produce with strings will get stuck around the cutting blade and cause more friction and heat. (especially Celery and leafy greens with long stems)
  • JUICE CONSISTANTLY and DRINK YOUR JUICE AS SOON AS YOU MAKE IT (DO NOT STORE IT) FOR HIGHEST QUALITY. THIS IS THE MOST IMPORTANT FACTOR, IN MY OPINION ABOVE ALL OTHERS. IT'S  MORE IMPORTANT THAN WORRYING ABOUT BOTH HEAT and OXIDATION.

I already own a centrifugal ejection juicer, do you think that's ok?
There is no doubt in my mind that people who juice regularly reap the benefits of juicing, regardless of the type of juicer they are using.  When I first started juicing, I used a centrifugal ejection style juicer, and loss weight, had more energy, and felt great.  You might want to read this article regarding purchasing a new juicer if you already own one.

If there was one juicer that you said heated the juice the most, which model would it be?
I would have to say the champion tends to heat the juice, and would heat the produce the most.  The champion operates in a way that the most friction is created at the highest rpm (speed).  This is intensified if your blade is dull, or you try to juice too fast.

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