# Estimating OG when only pre-boil gravity available

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

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.

• You really need the Belgian candy syrup as a weight, not a volume. For a correct gravity equations. Apr 6, 2018 at 3:33
• I looked for that before posting. I found the table sugar to invert syrup chemical formula and see a water molecule is added, but don't remember enough chemistry to know how much 2.5 lb table sugar turns into. That's probably a good but separate question.
– Dale
Apr 6, 2018 at 13:31
• Sorry my comment wasn't that clear. Without having both the weight and volume there's no way to calculate the gravity potential exactly because you don't know how much is water and how much is sugar. When as a syrup the maker should provide a gravity potential based on volumes IE (1/4 cup in 1gallon = 1.010 gravity). They do very a lot between makers. Apr 6, 2018 at 13:43

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.

• Thanks for the idea to relax into it. I did the ratio plus candi sugar points before posting, but wondered if someone here could put a finger point on it. Not because I "needed" to, but because this is an area where nurding out is socially acceptable.
– Dale
Apr 6, 2018 at 13:26

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.

• I added information to the original question. The candi syrup was a honey-like thickness and about 15% water.
– Dale
Apr 12, 2018 at 22:11