I often use invert sugar as a humectant in confections. The problem is that it always crystallizes after a few days.

My recipe is fairly simple.

  • 1 kg refined sugar
  • 200 ml filtered water
  • 1 g cream of tartar

Bring to boil at 110C. Let cool.

The syrup is definitely inverted, as the taste is distinct. The invert sugar is also completely transparent which tells me there are no obvious undissolved sugar crystals.

Crystallization typically begins slowly at the point where I insert a spoon to portion out the syrup for recipes.

I store the syrup at room temperature in a glass syrup jar. I have had no luck boiling the jar in water to liquify the syrup, as it appears saturated and it returns to the crystallized state. Also I suspect the boiling temperature is above 100C, which the waterbath cannot exceed.

  • Perhaps try the re-liquify step in a container over water in a pressure cooker? Would get the temperature up and also add a little bit of water from condensing steam.
    – Ecnerwal
    Commented Dec 7, 2016 at 14:29

5 Answers 5


The crystalization is to be expected, that's what inverted sugar does. It is the same thing as with honey, which is chemically nothing but a contaminated inverted sugar. So, you are not doing anything wrong. In an inverted sugar at sucrose ratios, you will get sucrose crystalizing back out of the solution, just as you are observing now.

If you really need it smooth, you can try changing the ratio by adding some fructose, as such a mixture is less prone to crystalizing.

The one thing that puzzles me in your description is that you cannot get it back smooth by heating, this should in principle be possible. Maybe try adding a bit of water to the syrup itself during heating, so it can dissolve again.

  • 1
    Crystals readily forming should be normal for a super-saturated solution, and it would get worse as water will continue to evaporate once the crystals form. Adding a small amount of water would likely help, but it may also take that original 110C which you won't git via water bath unless you also do something to the bath to raise its boiling point. It may take direct heat which will risk over-heating to pull it off.
    – dlb
    Commented Dec 1, 2016 at 15:33

My first guess would be your pan was dirty or not completely clean, happens quite a lot when boiling sugar that spits from the boiling cristalize on the side and "infect" the other sugar. Did you wash down sugar on the sites while it was boiling to reach the desired temperature?

  • 1
    I am fastidious when making candy - it is such a sticky process. I assure you the pan was clean before I began. I wash down the sides of the pan during the boil using a basting brush with hot filtered water. It never seems effective with invert sugar as the syrup is so thick. Perhaps that does introduce some sugar crystals.
    – TYale
    Commented Dec 1, 2016 at 13:51
  • 5
    @TYale Back from my school chemistry days, when dealing with a solution like that, it takes almost nothing in the way of contamination of the solution to start crystal precipitation. I single scratch in a jar, the edge of a spoon or a single sugar grain can do it, anything with an edge that closely approximates the shape of the crystal can act as the seed around which the crystals will grow. The more edges they see, the more the crystals will have seed points and the faster it can happen, but just one is required and almost impossible to avoid.
    – dlb
    Commented Dec 2, 2016 at 14:58
  • @dlb Invert sugar and honey are very close chemically, though honey has contaminates. How come honey doesn't crystallize as easily even when agitated just as much? On a related note, my invert sugar is typically much more viscous than honey - perhaps it is too saturated and the syrup should be diluted.
    – TYale
    Commented Dec 6, 2016 at 21:29
  • @TYale Here is one discussion of honey crystallization I found of interest: benefits-of-honey.com/crystallization-of-honey.html There remains some differences between your solution and natural honey. My understanding of honey has been different than some of stated in that article, but is based on hearsay, so they probably are more accurate, but I have always learned that closed containers help and that parts of the honey structure helps reduce evaporation. In the past corn syrup was often used to extend honey and why non-pure honeys tend to not precipitate crystals as readily.
    – dlb
    Commented Dec 7, 2016 at 14:03

From what you describe, I seems to me that sucrose in your syrup is just poorly hydrolyzed. In other words, the syrup still has a lot of sucrose so sucrose crystals form when possible:

  • when disturbed with a spoon
  • when heated up

The taste will be distinct anyway because of cream of tartar, so I doubt it's a robust criterion of invert syrup.

Possible causes:

  • boiling time. Time is crucial for sucrose hydrolysis and you haven't specify how fast do you boil it up to 110 C. From a huge sucrose/water ratio my guess is - not too much. I would suggest 20-30 min boiling time. You would need less heat, more water and more of CoT for that.
  • the quantity of cream of tartar. I know that 1g per 1kg sugar is a common recipe found on the internet, but it doesn't make any sense to me. Cream of tartar (and all possible acid substitutes) is not a reagent here but a catalyst and what matters is pH, thus, CoT's ratio to water. This is to keep in mind if you would consider increasing amount of water for longer boiling. As for you case the amount of cream of tartar is enough, though you may consider rising it up to 2g.
  • possible undissolved crystals. You said, you don't see any and that's a good sign. But there still might be really tiny ones. I would actually suspect them to be there because that amount of sugar only dissolves completely in that amount of water at 100 C and it seems it doesn't have much time to finish dissolving till 110 C when you start cooling.

Also, you may have luck using a microwave for re-liquification. Myself, I have always ended up scorching honey when I have tried, but many swear by it, and if you can do it with honey, you should also be able to do it with invert sugar solution.


I think your initial mix doesn’t contain enough water. When you start with 1 kg refined sugar, you should have used 500 ml of water instead of 200 ml.

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