Level:  Apprentice

Reading Time: 10 minutes

Is a humidity of 70% too high to temper with? 

I get variations of this all the time and from the phrasing of the question it is often apparent that  the meaning and role of humidity isn’t well understood by many people especially in regards to tempering.  Technically the term is relative humidity and that is important.  

I want to start by breaking apart the definition of relative humidity.  A lot of people think it is an absolute measure of how much moisture is in the air.  The first part of that directly contradicts this though.  It is a measure of the relative amount of moisture in the air.  Relative to what?  - the maximum amount of water that the air is capable of holding.  Think about this way.  Say you have a container that hold 100 oz of water.  If it has 40 oz of water in it then relatively speaking the cup is 40% full.  If you get a new container that holds 50 oz and put the same water into it, that cup is now 80% full.  So the amount of water is relative to the size of the cup.  

The air surrounding us is the cup and the ambient temperature is the size of that cup.  This is important because it shows that relative humidity changes as temperature changes.  What stays the same is the amount of water in the air.  In the above example if you magically shrink your container so it can only hold 35 oz then 5 oz of water is going to spill out.  In the air this is called condensation and is why water can form of cool surfaces (like your chocolate when you take it out of the refrigerator).  That brings us to another useful term called Dew Point.  In the air it is a temperature.  In our example it is the size of the container, 40 in this case.  If we shrink the container any more than 40 oz then water will spill out.  Said a different way if we drop the temperature below the dew point of the air (its water holding capacity) then water will spill out (condense).

If we look at the question again, it become pretty obvious that it is the wrong question.  Let me phrase it in terms of containers.

“Is it a problem that my cup is 70% full?”  

Why would that be a problem?  The answer is that it isn’t a problem in that it does not matter.  All we care about is when we shrink the container (lower the temperature during tempering) is the water going to overflow?  

To answer that question I have to introduce you to a chart that tends to freak a lot of people out.  It is called a Psychrometric Chart and I am going to show you how to use it.  This one is slightly simplified and only has the information we need on it.  Please just follow along and you should find it isn't too bad.

Dew point chart.jpg

On this chart 70% RH (relative humidity) is not a point but a curve.  It is this one.


What you didn’t tell me is the temperature you are work in and that makes all the difference because that is directly related to how much water the air can hold and when it will spill out and condense on your chocolate.

If you are at 80 F then you draw a line up from 80 until it intersects the RH line.



Then you draw a line left until it hits the 100% RH curve and read what the resulting temperature is.


It is 70  F.  That means that you can refrigerate your chocolate down to a surface temperature of just over 70 F and pull it out of the refrigerator and no water will condense on the bars.  If you go to 70 F or lower then when you pull them out water is going to condense on the bars.  To be clear we are talking about the chocolate temperature, not the refrigerator temperature.

There is no guess work involved and no need to wonder if your RH is ok or not.

Now if you room temperature was 70 F that changes everything.  Let’s look at that chart.  Remember, find your temperature along the bottom, follow it up to your Relative Humidity, go left to where it meets the 100% RH curve and follow it back down to read your Dew Point (the point dew/water forms).


Now you can chill your chocolate down to 59 F without any problem. 

I want to make a point though.  I didn’t say if you cooled your room down to 70 F.  I said it was naturally at 70 F.  There is no guarantee that cooling your room down will reduce the moisture content of the room.  If it does not then all you are doing is changing your cup size. 

Look what happens if you cool your room that is 80 F and has a 70% RH down to 70 F without adjusting the moisture.



What happens is that you hit the 100% RH line at the same time.  You have hit the Dew Point and water is going to condense out of the air.  That of course is only if your air conditioner isn’t pulling water out of the air and most of them they are.  I just wanted to point out that JUST dropping the temperature isn’t a solution.

Most likely if you cool your room with an air conditioner you are also going to reduce the total moisture in the air but I can’t tell you how much.  It all depends upon your air conditioner and its capabilities.  You will have to measure it.

Just for the sake of an example, let’s say your air conditioner reduces the temperature from 80 F/70% RH to 70 F/60%.  You are now working on this curve and you can see you can refrigerate your chocolate all the way down to its 55 F Dew Point without any problems.



The last thing that I want to point out is why I so often say humidity does not matter as long as it is under 100% AND you are not refrigerating your chocolate.  It is because it doesn’t matter. My definition under those conditions you are above the Dew point so water won’t condense on your chocolate since the chocolate can only get as cool as the room.

  • If the temperature of the chocolate is below the dew point of the room then moisture will form on the chocolate.  
  • If the temperature of the chocolate is above the dew point of the room then moisture cannot form on the chocolate.

And with your new Psychometric chart tool to work with all you have to do is look your conditions up and KNOW how much you can chill your chocolate before there will be an issue.  No guess work involved!   

Happy tempering everyone. 

Oh, and speaking of tempering, we have a new Sous Vide available so you can make your own Silk.   The Nomiku with Wifi.