How can I prime by taking the gravity of the priming fluid?

I have this great mulberry syrup I found. I want to prime with it, and I forget how to figure this out with an unknown sugar source. I see that John Palmer's "How to Brew" references measuring the gravity of honey (a variable ingredient) to figure out priming rates in How to Brew, but he mentions you could dilute it and measure it with your hydrometer.

So, say you have some awesome backyard beekeeper's honey or other lovely sticky stuff you want to dilute into a priming liquid. What steps do you take, and what's your math to figure out how to get, say, 2.5 volumes of CO2 into a 3 gallon batch of beer? Or even a 5 gallon batch.

Topic honey priming-sugar original-gravity carbonation homebrew

Category Mac

1
answered at

If you follow a process like this, you won't be far off:

  1. Dilute the syrup to create a 10% solution. E.g. add 10g of syrup to 90g of water and stir well.
  2. Take the specific gravity of the 10% solution, e.g. 1.030
  3. Express this as a fraction of a 10% solution of sucrose, which has specific gravity 1.040. So, our example of 1.030 is .75 the gravity of a 10% sucrose solution.
  4. Use a priming sugar calculator to determine how much sucrose to prime with. E.g 100g.
  5. Divide this number by the fraction derived in 3. E.g 100g/.75 = 133g. This is how much of the undiluted syrup you need for priming.

Please note that this only an approximation because we're not accounting for the increase in volume from the added priming syrup. If the syrup is very sweet (like honey), the effect of the additional volume is negligible. If it's not particularly sweet (like fruit juice, e.g.) then the effect is large.

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