Article by: Perry Romanowski

I was sent an email asking me about what the best set-up was for heating batches.  It seemed that this formulator was having a hard time getting her batches to heat up quickly.  I told her the setup I typically use includes the following

  • 1.  Beaker (for the batch ingredients)
  • 2.  Stainless steel short pot filled with water (for the water-bath)
  • 3.  Hot plate

Then you should also cover the batch with Aluminum foil and plastic wrap.  This set-up works well.

However, in considering this question it occurred to me that there is a phenomena that most emulsion formulators will experience some time in their formulating career.  When you are heating your oil phase, it will get hotter much faster than the water phase.  In fact, it can almost seem like it gets hotter twice as fast.

The reason?

Our good old friend the Hydrogen Bond.

The temperature of a system is a reflection of the speed at which the molecules in it are moving.  Water molecules tend to stick to each other better than oils stick to each other.  That is because of hydrogen bonding between molecules.  So, it takes more energy to break the hydrogen bonds and speed up the molecules.  In an oil phase, there isn’t that extra bonding between the individual molecules so it requires less energy to make the molecules go faster and heat up.

And if you want to test this for yourself, try this water oil heat capacity experiment.

10 comments

  1. moira

    Hi Perry,
    I more frequently seeing people suggest heating and holding the oil phase and the water phase – is this necessary. When I first started formulating I was taught that only the water phase needed to be heated and held for 20 minutes to help reduce microbial levels and it was only necessary to ensure both phases were at 70°C before combining.

    Also I have also always added an additional 10% of water before heating to account for any evaporation then weigh it once heated to ensure I have he correct amount. Is this the best way to do it?

    Thank you.

    1. Perry Romanowski

      If you are using water that is not contaminated then you don’t really have to hold the water at a high temperature for extra amount of time. It also makes little sense to hold the oil phase at a high temperature before mixing.

  2. Chris

    If we cover the phases up with foil won’t that cause condensation and thus rendering the sterile water not sterile anymore?

    1. Perry Romanowski

      Your water phase isn’t sterile whether it’s covered or not.

      1. Chris

        So I shouldn’t worry about condensation then?

        1. Perry Romanowski

          If you have a properly preserved formula you don’t have to worry about it.

  3. Jane Barber

    Thanks Perry.

    Another question – the batch will be more fluid at higher temps = smaller miscelles. So is there an argument to add, the majority of the estimated evaporated water amount at the start rather at the end as the emulsion will be a higher viscosity at cool down?

    1. Perry Romanowski

      The best thing would be not to have any evaporated water but adding the small amount at the end should not be a problem.

  4. Jane Barber

    That’s interesting Perry. Do you cover only the water phase (not oil phase) with foil/cling film during the 20 min heat and hold – to keep the heat in and less water evaporating ? (Also do you make up the lost water at the end or do you add, say 10% extra at the start to account for evaporation and then weigh again at end?)

    Personally, I find my oil phase takes longer to reach 70c than the water phase but that’s because I have a high % of hard oils.

    1. Perry Romanowski

      Hello Jane – I covered both the oil and water phases. One was to prevent evaporation, the other was to just ensure that nothing gets accidentally dropped in the batch. Yes, I did add back any lost water at the end.

      I suppose you are correct that different oil phases will take different amounts of time to heat up.

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