Big_Eddy
10-27-2014, 02:36 PM
I had a member ask me recently why he shouldn't just buy a big evaporator, even though he was planning to start with only a few trees. He doesn't want to spend his whole life tending a fire, and everyone else is telling him to plan for growth after he's bitten by the maple bug. I thought I'd share my thoughts with all members.
The original question was - why not just get an evaporator that can boil off 30 gals / hr? Then I only need to boil an hour every day or two?
The problem arises when you calculate the minimum amount of sap needed for a boil. At 30 gals / hr, that would be 30 sq ft of surface area, or 7.5 gallons of syrup at 3/8" deep. To make 7.5 gallons of syrup, you need to start with 300 gallons of sap. With 30 trees, that could be 2 full weeks sap, which would have likely spoiled before it was boiled. And you can't start with 150 gals and boil it half way then wait for more. That 50% concentrate is a perfect environment for bacterial growth. So you need a pan small enough that you can boil it to syrup a minimum of once a week.
Below is the logic I use when asked about flat pan sizing. Hope it helps someone.
First some round numbers to work with.
A typical sugar bush (on buckets) will average about a gallon a tree per running day (maximum of 2 gallons/tree), with 3-5 running days a week. I use 5 gallons a tree a week as a maximum number. Those on tubing and vacuum might have to double those numbers.
Each tree tapped will produce an average of 10 gallons sap a season (1 qt or litre of syrup)
A flat pan evaporator boils off ~1 gal / sq/ft / hr with normal firing and no preheat. Add a blower and preheat and maybe 1.5 gal/hr.
3/8" deep is as shallow as you can effectively boil.(That's ticking over at the very end - not all the time!!!)
1 quart of sap or syrup ~=3/8" on 1sq ft.
Sap to syrup ratio is 40:1
You can tweak the numbers above if needed, but they give us a baseline to work from.
Everything below is based on a flat pan and batch boiling. I've done similar math for a continuous flow process in the past. Follow the How Much to Sweeten link.
Sap needed for a batch boil - Rule of thumb - pan size in sq feet x 10 gallons.
Sap needed = sap:syrup ratio x pan size x 1/4 gals/ sq ft
For a 2x3 pan = 40 x 2x3 /4 = 60 gallons of sap.
i.e. if you start with 60 gallons of sap, you will have 3/8" left in the pan when it gets to syrup. Any less sap to start and you can't boil it down to syrup without going under 3/8" deep, or pouring it off into a smaller vessel.
Hours per boil - Rule of Thumb - Gallons of sap / sq ft of pan
For a 2x3 pan, and a 60 gallons of sap, Hours = 60 /(2x3) = 10 hours boiling.
Suitable Pan Size - Rule of thumb - 1 sq /ft for every 5 trees.
5 trees x 5 gals/ week = 25 gals/wk.
25 gals = 25 hours boiling @ 1 gal /hr/sq ft. (25 hours ~= 3@8hours)
For 30 trees, a 2x3 pan is perfect.
30 trees x 5 gal/tree / 6sq ft = 25 hours boiling average
Of course, not every week is average, so there will be lighter weeks and heavier weeks. I ran a 2x3 pan with 100 trees for years - but there were many late nights and the occasional time when sap was dumped.
The original question was - why not just get an evaporator that can boil off 30 gals / hr? Then I only need to boil an hour every day or two?
The problem arises when you calculate the minimum amount of sap needed for a boil. At 30 gals / hr, that would be 30 sq ft of surface area, or 7.5 gallons of syrup at 3/8" deep. To make 7.5 gallons of syrup, you need to start with 300 gallons of sap. With 30 trees, that could be 2 full weeks sap, which would have likely spoiled before it was boiled. And you can't start with 150 gals and boil it half way then wait for more. That 50% concentrate is a perfect environment for bacterial growth. So you need a pan small enough that you can boil it to syrup a minimum of once a week.
Below is the logic I use when asked about flat pan sizing. Hope it helps someone.
First some round numbers to work with.
A typical sugar bush (on buckets) will average about a gallon a tree per running day (maximum of 2 gallons/tree), with 3-5 running days a week. I use 5 gallons a tree a week as a maximum number. Those on tubing and vacuum might have to double those numbers.
Each tree tapped will produce an average of 10 gallons sap a season (1 qt or litre of syrup)
A flat pan evaporator boils off ~1 gal / sq/ft / hr with normal firing and no preheat. Add a blower and preheat and maybe 1.5 gal/hr.
3/8" deep is as shallow as you can effectively boil.(That's ticking over at the very end - not all the time!!!)
1 quart of sap or syrup ~=3/8" on 1sq ft.
Sap to syrup ratio is 40:1
You can tweak the numbers above if needed, but they give us a baseline to work from.
Everything below is based on a flat pan and batch boiling. I've done similar math for a continuous flow process in the past. Follow the How Much to Sweeten link.
Sap needed for a batch boil - Rule of thumb - pan size in sq feet x 10 gallons.
Sap needed = sap:syrup ratio x pan size x 1/4 gals/ sq ft
For a 2x3 pan = 40 x 2x3 /4 = 60 gallons of sap.
i.e. if you start with 60 gallons of sap, you will have 3/8" left in the pan when it gets to syrup. Any less sap to start and you can't boil it down to syrup without going under 3/8" deep, or pouring it off into a smaller vessel.
Hours per boil - Rule of Thumb - Gallons of sap / sq ft of pan
For a 2x3 pan, and a 60 gallons of sap, Hours = 60 /(2x3) = 10 hours boiling.
Suitable Pan Size - Rule of thumb - 1 sq /ft for every 5 trees.
5 trees x 5 gals/ week = 25 gals/wk.
25 gals = 25 hours boiling @ 1 gal /hr/sq ft. (25 hours ~= 3@8hours)
For 30 trees, a 2x3 pan is perfect.
30 trees x 5 gal/tree / 6sq ft = 25 hours boiling average
Of course, not every week is average, so there will be lighter weeks and heavier weeks. I ran a 2x3 pan with 100 trees for years - but there were many late nights and the occasional time when sap was dumped.