Question on Rule of 86

[jrgagne99]

I have a question about the Rule of 86.

If syrup has 66% sugar content, and you started with sap that had 2% sugar content, logically the ratio of sap to syrup would be 66/2 = 33:1. But the Rule of 86 says that the ratio is 86/2 = 43:1.

Does anyone know what is the reason for this apparent discrepancy?

[DaveB]

My understanding is that the Rule of 86 is the number of gallons of water that you have to boil off in order to wind up with syrup. If you think about it, the syrup is still 34% water. With your 2% sugar content sap, you needed to boil off 43 gallons of water to wind up with a product that is now 66% sugar or syrup.

Dave

[StewieSugar]

I got a slightly different impression.

I believe the discrepency is that the Rule of 86 is based on volume (gallons), where sugar content (Brix) is measured in weight (pounds). Meaning, the Brix level is the ratio of the weight of the sugar relative to the weight of the syrup, and it's not based on the how many gallons of sugar.

If everyone used volume, then the 33:1 would be correct. Or, if everyone used weight, then the 33:1 would be correct as well. The narly part is that folks are using different measurement sticks (kind of like metric versus English units).

As I found out recently, syrup is heavier than water. Per a different thread on these forums, pure water is about 8.3 pounds per gallon, where 66% syrup is around 11 pounds per gallon - the heavier weight due to sugar. If sugar and water weighed the same, then syrup would weigh the same as water.

Sugar is heavier than water (I don't have an exact number). So, if you increase the sugar weight by 33:1, you need to decrease the water by more than that to compensate for water being lighter.

That's my impression; anyone know for sure?

[jrgagne99]

I emailed Steve Childs at the Cornell Maple Program. His repsonse makes perfect sense:

John, The discrepancy comes from the difference in weight of sugar and the weight of water. The Rule of 86 is calculated by dividing the weight of sugar in a gallon of 65.5 brix syrup (7.2115 pounds) by the weight of sugar in a gallon of sap at 1 brix (0.0836 pounds). The answer, 86.26 represents the number of gallons of 1 % sap that must be evaporated to produce syrup with a density of 65.5 Brix. The 65.5 brix was used in the old days when the rule was invented with the current syrup density of 66 it should be more like the rule of 87. In other words you are evaporating the lighter part of the volume and keeping the heavier part of the volume so more volume must be evaporated to get the end result than if the sugar and water were of equal weight. Hope this answers your question. Thank you. Steve Childs

Now I can sleep at night again...