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Thread: Rule of 87 or 86

  1. #1
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    Default Rule of 87 or 86

    We just were thinking about the rule of 86 or 87 depending on if you are in VT or not. To figure how much sap makes a gallon of syrup you divide 87 by your sugar content. Simple, 2%sap 86/2 it takes 43 gallons of sap to make a gallon of syrup. Well we have 100 gallons of 12% sap and wanted to know how much syrup we will have when we are done. Rule of 86 is 86/12 =7.25 100 gallons 100/7.25 = 13.79 gallons of syrup. Here is where I get confused. If I have syrup at 66% sugar then the rule of 86 would say it takes 1.3 gallons of syrup to make a gallon of syrup. This makes no sense. Can some one clear this up? Thanks
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    its syrup at 66%. i think the rule of 86 is just an "estimate" so your not dividing your sugar content by 86.1 or 86.2, cause it would obviously be harder that way. i could be way wrong here though.

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    Quote Originally Posted by MillbrookMaple View Post
    Well we have 100 gallons of 12% sap and wanted to know how much syrup we will have when we are done. Rule of 86 is 86/12 =7.25 100 gallons 100/7.25 = 13.79 gallons of syrup. Here is where I get confused. If I have syrup at 66% sugar then the rule of 86 would say it takes 1.3 gallons of syrup to make a gallon of syrup. This makes no sense. Can some one clear this up? Thanks
    This came up a couple of weeks ago. The rule only works for sap with sugar concentrations you might normally expect from the tree. That's what the formula is based on, not sap that has been concentrated. In sap taken directly from the tree, brix and sugar weight /volume are roughly equivalent so the math works.

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    if you do the math backwards for 12% sap by "diluting" down to 2% sap instead of 100 gallons you would 600 gallons and by applying the the rule of 86 you will still get the same amount of syrup 13.95 gallons approx. the "breakdown" only occurs for finished syrup, i think this is due to the fact that it does not take into account the volume of the syrup minus the sugar, which is approx. 34%, which breaks down to roughly 1/3 of gallon and this is where you come up with 1.3 gallons to make 1 gallon syrup. it would take 1.33 gallons of 66% sugar/syrup concentrate to make 1 gallon of 100% maple/sugar concentrate.
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    Quote Originally Posted by bowtie View Post
    if you do the math backwards for 12% sap by "diluting" down to 2% sap instead of 100 gallons you would 600 gallons and by applying the the rule of 86 you will still get the same amount of syrup 13.95 gallons approx. the "breakdown" only occurs for finished syrup, i think this is due to the fact that it does not take into account the volume of the syrup minus the sugar, which is approx. 34%, which breaks down to roughly 1/3 of gallon and this is where you come up with 1.3 gallons to make 1 gallon syrup. it would take 1.33 gallons of 66% sugar/syrup concentrate to make 1 gallon of 100% maple/sugar concentrate.
    The formula only works with sap at normal sugar concentrations as measured directly from the tree for the reason I mentioned. It is based on sap as collected and will not work at higher concentrations of sugar since brix value and volume/weight will not be equivalent at higher concentrations.

    Jones rule of 86 as explained in an old 1970's copy of the "Maple sirup producers manual "
    http://www.archive.org/details/maple...oduc00willrich

    "Since the solids concentration of sap is comparatively low, its Brix value and percentage of solids (weight-volume) are essentially the same. Therefore, the percentage of solids (weight-volume) of the sirup divided by the Brix value of the sap equals the number of gallons of sap required to produce 1 gallon of sirup."

  6. #6
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    you can not deny the math though. it should not matter what the concentrate is if it started at roughly 2% from the tree, you need only back figure the amount started with if you use an r/o. the figure 66% is not a brix value but % of sugar in maple syrup. maybe wrong but if do the math it should work out.
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    Jones rule of 86 was made in 1933, and Vermont Syrup standard at this time was 65.5 brix. thats why it have to be adjust now.
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    Quote Originally Posted by bowtie View Post
    you can not deny the math though. it should not matter what the concentrate is if it started at roughly 2% from the tree, you need only back figure the amount started with if you use an r/o. the figure 66% is not a brix value but % of sugar in maple syrup. maybe wrong but if do the math it should work out.
    You almost lost me on the math but that's not surprising given my fear of math lol. But that said, where did you get 34%? The rule of 86 takes weight by volume into consideration, not just weight or volume alone. And 66 brix *does* mean 66% sugar so not sure why you say it does not. What I think you're not considering is what that 66% sugar accounts for in the weight of a gallon of syrup. It is not 66% but 86%.

    Anyway, as I understand it, in 2% sap the sugar content accounts for about 2% of it's weight by volume thus brix and weight by volume are equivalent. In a gallon of syrup at 66 brix, the sugar accounts for about 86% of it's weight. This is where the 86 comes from in Jone's rule. Thus the weight of water accounts for only 14% of a gallon of syrup's weight by volume (not 34%) and the formula will not hold because 66 brix is not equivalent to 86% sugar by volume weight.

    CBoyer is right, since the brix of finished syrup has been increased a little over the years, the rule of 86 is more of an estimate these days but it stills works as a good guestimate. But even back when the rule was first postulated it was never meant for calculating anything but the sap to syrup ration of sap straight from the tree. At higher sugar concentrations it just doesn't work.
    Last edited by happy thoughts; 03-27-2012 at 07:51 PM.

  9. #9
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    When we read a hydrometer and it reads 2, it means 2 degrees Brix, not 2%. the Brix scale and percent scale are very close when we are reading at relatively low sugar contents as found in sap. the higher up the scale you go the farther the 2 scales diverge. That is why when we get to syrup density you see that 66 does not equal 86.
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    A hydrometer measures soluble solids in sap or syrup, of which sugar comprises roughly 98%. As sugar is concentrated so are the other soluble solids. That accounts for the variation between Brix and %sugar. Also, at 66.9 Brix (VT min density) we need to replace 86 with 88 for the constant in Jones rule.
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