Two sugar plus one(ish) water equals? Calculating sugar syrup volumes

25kg sugar and 12.5 litres of water just doesn’t fit!

It’s over now, but the last few months I’ve been making up large amounts of sugar syrup to feed the bees for the winter. This year I bought in bulk 25kg bags of sugar from my local Booker wholesaler, whereas in previous years it has often been cheaper to buy in from a local supermarket.

In the autumn the usual recommendation is that we feed a “thick” syrup, of roughly 2 parts sugar by 1 part water (weight for weight). This feeding is designed to help the bees survive the winter and is only fair after I’ve taken a honey crop.

My general technique for making the syrup is to heat the water to boiling then add the sugar, turn off the heat and stir until dissolved. Sometimes I’ll add slightly more water than the recipe to make it easier to get the sugar to dissolve.

I’m always left with the same question, how much syrup will it make? If I mix say 25kg of sugar with 12.5 litres of water how much syrup will it yield? I know as it dissolves the volume of the water increases, so it’s going to be more than 12.5 litres, and I know it’s going to be less than 37.5 litres (as it doesn’t go up by a whole litre per kilo)!

You’re probably asking why I care, there are two reasons:

  • I treat my sugar syrup with thymol to stop it going mouldy. Feeding often extends over a period of weeks, in Setpember and October, and without the thymol the syrup can go mouldy/ferment. As per National Bee Unit Guidance (here), this requires a certain dosage per litre of syrup (2.5ml to 4.5l in that case). So knowing how much syrup is produced is essential for this.
  • I’d like to know it’ll fit in the stainless steel pot I use for mixing, as I know from bitter experience boiling up 12.5 litres of water and then adding 25kg of sugar doesn’t fit in my 30 litre pot, so what will ….

Anyway, it seems I’m not the only one. Others have asked the same questions on the usual forums (e.g. https://beekeepingforum.co.uk/threads/what-is-the-formula-for-calculating-how-much-sugar-sugar-syrup-contains.31701/) and frankly if you can understand the answer from this thread then well done!

So, I decided to research the issue, found some really helpful information over at Vinolab (here) and after a bit of head scratching managed to make sense of it. I’ve then set it up as a calculator below.

Use at your own risk etc, but in case it is of use.

To use the calculator:

  1. Enter the amount of sugar you would like to use
  2. Select a syrup thickness, or custom to define your own amount of water
  3. The yield of syrup is given at the bottom