Estimating OG when only pre-boil gravity available

Question

Is it possible to estimate the post-boil specific gravity given only a pre boil gravity reading, plus volume measurements, while also accounting for a invert sugar syrup addition?

For example, say the facts were as follows:

• 7.59 gallons at hot break
• 1.062 specific gravity at hot break
• 0.35 gallons¹ Belgian candi syrup added
• 6.70 gallons at flame out

Edit / Addition:

The 2.5 pounds of table sugar that was used to make the candi syrup is said to have 46 ppg (points per pound per gallon), so supplied 115 points. The reason for calling out this fact is that this eliminates the need to have a measure on the candi syrup directly.

Footnotes:

^{1. An approximation. Made from exactly 2.5 lb granulated cane sugar, but don't know the conversion to volume. Brewing software adds 0.013 to specific gravity when added. Edit / Addition: the candi syrup turned out to be about 15% water.}

Answer 1

Calculation of post-boil gravity, should no additions be done, is preboil_gravity*preboil_volume/postboil_volume.

Water volume addition from the candi syrup is negligible, so just add that 0.013 gravity points to the calculated post-boil gravity, and you should be fine.

I wouldn't bother trying anything more precise than this estimate, since measuring with hydrometer already has some error in it (due to temperature, viewing angle, bubbles etc). With variations in fermentation process, in the end, unless you're far out of the ballpark (like, >0.01), no one will likely notice.

Answer 2

You have an unknown in this equation. Gravity potential of the syrup.

- 7.59 gallons at hot break
- 1.062 specific gravity at hot break
- 0.35 gallons Belgian candi syrup added
- 6.70 gallons at flame out

Without knowing the water sugar ratio of the syrup "estimates" will have a wide range.

I've seen "syrups" as thick as honey, while others are as light as apple juice.

Update: If 6.7gal was total ending brew volume and 2.5 lb dry weight of sugar was used to make the syrup. Then you do have everything to calculate it. OG 1.088 Method using basic brew calculator. Set efficiency to 100% Make a recipe of 7.59 boil volume add any adjunct to get OG to 1.062. Then add the 2.5lb of sugar with a gravity value of. 1.046. Set final volume to 6.7 gal.