Calculation for Sap before draw off

[MillbrookMaple]

I was having a debate last night with my buddy about why we had enough sap to make 25 gallons of syrup and we only drew off 18. I told him that it takes a bunch of gallons to fill the machine and then a bunch more to evaporate until the first draw and that is our differance. I could find this out a couple of ways. 1 Actually measure how many gallons I used from fill to draw. 2 Pull all the sap from the evaporator measure the volume and sugar content and calculate how many gallons it took to get there. Does anyone have a calculation based on size of the evaporator for this number?

[Big_Eddy]

I'm assuming this is a first boil and you were filling the evaporator and sweetening it as part of the process.

Below is the math to determine how much sap is required to sweeten pans. For your purposes, subtract this amount from your starting sap quantity and then divide the remainder by your sap:syrup ratio to see how much you will actually produce. Once sweetened - all subsequent boils will produce at your normal sap:syrup ratio.

Working in metric units.

Number of litres to fill the pans = [(evap width in cm x evap length in cm x usual depth in cm) + (Num Flues x width of flues x depth of flues x length of flues)] all divided by 1000

Sap to sweeten pans = Number of litres x sap:syrup ratio / 2

Convert to US gallons by dividing by 3.78 l / 1 US Gal



Example - running 1.5" deep on a 2x6 with a 4' drop flue pan (6 flues 7" deep by 1" wide)

Volume =[ 60cm wide x 182cm long x 4cm deep + 6 flue x 2.5cm wide x 120 cm long x 18 cm deep ] / 1000
_______= [43680 + 32400 ] /1000
_______= 76 litres or 20 US gals

Assuming a 40:1 ratio.
Sap to sweeten = 76l *40 / 2
______________= 1520 litres or 400 US gals.


The calculations above are based on a continuous flow process with an evaporator design that permits establishing an even gradient through the evaporator. Any mixing between sections will increase the amount of sap required before the first draw off. If you have no flues in your pan, just use 0 for the number of flues and the rest is the same.

[Starting Small]

What does it mean to sweeten the pans? I always thought it was just slang for the first boil of the year.

[Big_Eddy]

Starting Small.

In a continuous process, the pans are not emptied at the end of each boil, rather the "sweet" is left in the pans for the next boil.

Sweetening the pans refers to the first boil, where the pans start with raw sap throughout, then as you boil and boil and boil without any drawoffs, the gradient develops in the pans until you have raw sap at the inlet and "almost syrup" at the outlet. For a 2x6, this is roughly 400 gals of sap boiled down without any syrup produced and can be up to 20 hours of boiling.

Once the gradient is in place, then syrup starts to flow out at the usual ratio i.e. for every 40 gals boiled off, 1 gal is produced.

After each boil, we allow the rig to cool and close the valves between sections to maintain the gradient. Then when we start up the next day, the gradient is already there and syrup is produced "right away".

The pans are only emptied at the end of the season or for cleaning, and afterwards the gradient needs to be established again.

[Starting Small]

The more I learn the more I realize how little I actually know! Thanks for that, it makes more sense now.

[Big_Eddy]

The above is primarily designed for a flue pan, where the sweet is left in from run to run.

Don't think your Mason 2x3 has flues, so you can run it either as a batch process or as a flow process assuming you have dividers in it.

A 2x3 without dividers needs about 70-80 gals to make a batch. Start out about 2"-3" deep and just keep adding and adding as sap evaporates until all 70 gals are in, then reduce until you have about 1/2" in the bottom and that's pretty close to syrup. Let the fire go down when you're at 3/4", and pour it off into a pot before you get to 3/8". Finish on propane or stove.

A 2x3 with dividers run as a continuous process will evaporate about 40 gals of sap before you're ready to take your first draw, after which you can take off maybe a quart at a time every 2 hours or so. Before the end of the day, you need to decide if you're going to finish everything in the pan, or leave the sweet in the pan for tomorrow. Typically the sweet would be left in.

If you want to finish it all, then you switch back to batch mode and mix the pan around so that you have an even concentration throughout the pan, then reduce it all from there. Make sure you have enough sap when you switch modes to ensure that you're still 1/2" deep when done.

[Starting Small]

That is terrific information, I really appreciate it. It does have dividers so there are three compartments for continuous flow. I will probably leave the sweet in the pan. Can I leave the sweet there if I am not able to evaporate the next day? Would it keep alright for 2 or 3 days between boils?

[GOwin]

Thanks for sharing Big_Eddy.

I made an online sap volume calculator (https://docs.google.com/spreadsheet/ccc?key=0ApWpP2dZfyPfdHlUTFdNUHptZEp3aHpXVW1tcjcwc Gc) based on the formula you posted.

By the way, in case anyone is wondering why the numbers are off using the example posted by big_eddy. It's because of how we rounded off numbers. The spreadsheet used up to 2 decimal places in all calculations, while in eddy's formula he just dropped those numbers off.

[sg5054]

GOwin,
Am I missing something? I tried the calculator but it doesn't allow me to change the blue numbers.

[jmp]

sg5054 you have to download to your PC and use in Excel.

[Big_Eddy]

I've had queries as to why it's taking twice as much (or half as much) sap as calculated to sweeten. This is where evaporator design and operation comes into play. The size and shape of the pans, the number of dividers, number of flues, and the design of the arch as well as the sap depth and firing rate all affect the way the gradient develops. My math assumes a linear gradient from inlet to outlet. It's not that simple.

An evaporator with a lot of flue area, is going to evaporate most of the water in the flue pan. The liquid coming out of the flue pan and into the syrup pan could be pretty close to syrup and just needs a bit more heat before it can be drawn off. A similar sized evaporator with a flat sap pan and the heat concentrated under the syrup pan will do the bulk of the evaporating in the last section, and the concentration exiting the sap pan will be a lot lower.

More sections / dividers will reduce the mixing within the evaporator and result in a steeper gradient, as will running shallower. Uneven firing, and any fluctuations in sap level will cause mixing, and increase the amount of sap needed before syrup is produced.

The reality is that it doesn't really matter. As long as sap is going in one end and steam is coming off, eventually there will be syrup ready to take off at the other end. The math should help to understand roughly how much sap to have on hand to sweeten your rig and why. As a rule of thumb, plan to boil for most of a day before seeing any syrup out.

[maple flats]

On a flat bottom pan, you will boil much faster if you only have the depth at 1". However you must maintain that depth by slowly and continuously adding sap to keep that depth. When I used a 2x3, I started with about 1.5" depth until I got comfortable with the process, then I gradually dropped that to 3/4-1". I had a warming pan on top with a outlet and small valve to maintain the depth. Then I kept a close eye on the depth and tweaked the valve to hold that depth. Each time the warming pan got down to about 1/2 full, I added more sap to it.
At 2-3" deep you have more room for error but you likely lose up to 1/3 of your evaporation rate.

[Fort Wisers]

I'm on a thread revival role today LOL.

Really great thread, learning so much these days!
Thanks for the great information.

[carterwjeff]

The following pic is our sap brix readings before feeding it into the evaporator and its estimated calculations based on 87.1. I drew off today just before adding the last bit of sap. Ended up with 1.8 litres of syrup. So I am new to this but believe this means my pan is sweetened. If you look at my fluctuating ratios (due to me testing the throw out your ice theory) that sap will have different brix depending on mother natures conditions, therefore it will just be a broad guess when figuring how much sap until the pan is sweetened.

22220

22221

[Sugarmaker]

The following pic is our sap brix readings before feeding it into the evaporator and its estimated calculations based on 87.1. I drew off today just before adding the last bit of sap. Ended up with 1.8 litres of syrup. So I am new to this but believe this means my pan is sweetened. If you look at my fluctuating ratios (due to me testing the throw out your ice theory) that sap will have different brix depending on mother natures conditions, therefore it will just be a broad guess when figuring how much sap until the pan is sweetened.

22220

22221

Exactly what Jeff said!:)
Regards,
Chris

[berkshires]

Sap to sweeten pans = Number of litres x sap:syrup ratio / 2


I know it's been nearly 10 years since this post, but I just saw it for the first time recently. Most of the formula and description makes perfect sense, but I'm struggling to understand this part ^^^

It seems to me that the part of the formula above does not take into account the number of channels. I'm still working out the physics to prove it, but my intuition is that the more channels you have, the quicker the gradient should be established. Simple thought experiment: Suppose you had hundreds of little tiny channels: the amount of syrup you would have to make in the last channel would be tiny, so it would not take long.

Gabe

[maple flats]

I never kept track of exactly how many gal went into the pans before my first draw, I just knew it always took longer than I thought it should. Any formula would need to factor in the sap sugar % (or the concentrate sugar %), along with the capacity of the flue pan and the syrup pan. I found mine usually had gotten between 400-500 gal of raw sap, sometimes 600 gal before my first draw. After that draws were quite regular.

[DrTimPerkins]

...but my intuition is that the more channels you have, the quicker the gradient should be established.

The gradient isn't affected by the number of channels -- it is a function of the amount of water that has been removed based upon the position within the evaporator.

Think of an evaporator as a single, long, continuous channel with even heat throughout the entire thing (we'll ignore the backpan/fluepan vs syrup pan for simplicity) and an even boil happening across the entire pan. Assume that sap is going in at one end, and syrup is going out at the other in a continuous flow. The gradient will develop in proportion to the amount of water evaporated off, so let's say that 42 gal of water has to be boiled to make 1 gal of syrup drawn off. Starting with sap at 2 Brix coming in and 66.5 Brix going out, at the half way point, 21 gallons would be boiled off...but the Brix would only be 4 at that point. It has to go from 4 to 66.5 in the remaining half of the pan. So if we go half way from half way to the drawoff (75% of the total distance), we'd have boiled off 31.5 gal of water, leaving 10.5 gal left to boil to make 1 gal syrup. That puts us at 8 Brix. The next half way to the end brings us to 16, then 32, then 64 (close to 66.5 Brix). The water evaporation rate is constant (relatively so) from sap inlet to syrup drawoff, so the liquid remaining to be boiled off is represented by a straight line (blue). The sugar content however is not linear....it is exponential (red) or a doubling function.

You can see this in the temperature elevation if you measure it across a gradient. Very slow rise at first, very rapid when you get to the last few partitions. The "hill" or gradient" gets far steeper as you get close to the end. That is because temperature elevation is due to the amount of sugar that is in solution, so it reflects the density of the gradient.

Now most evaporators aren't quite that simple, but that is the basic process. Then you add on the bells and whistles (Steam-away, flue pans, max pans, RO concentrate, etc.) to complicate things and the fact that most smaller evaporators are not entirely continuous, but the analogy is still pretty close to what is going on.

These curves are also a good demonstration of why the RO process for sap is so energy efficient. Even at moderate levels of RO concentration you are already approaching the steep (efficient) part of the curve. The higher you are in the curve, the more efficient the process in terms of time and energy (or put another way, the less time and energy you still have to put into the system by boiling to make syrup).

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[HazensNotchSugarShack]

I never kept track of exactly how many gal went into the pans before my first draw, I just knew it always took longer than I thought it should..

At the beginning the first draw takes forever. (I think the ghosts of past sugarmakers sneak some of it.)

At the end getting one last draw off takes an eternity!!

[Big_Eddy]

I know it's been nearly 10 years since this post, but I just saw it for the first time recently. Most of the formula and description makes perfect sense, but I'm struggling to understand this part ^^^

It seems to me that the part of the formula above does not take into account the number of channels. I'm still working out the physics to prove it, but my intuition is that the more channels you have, the quicker the gradient should be established. Simple thought experiment: Suppose you had hundreds of little tiny channels: the amount of syrup you would have to make in the last channel would be tiny, so it would not take long.

Gabe

As Dr Tim stated, regardless of the number of channels, we assume that there is an even gradient from the inlet of the channel to the outlet. At the inlet, you have raw sap. At the outlet,you have pure syrup boiled down at 40:1 or 32:1or...
The AVERAGE density in the pan is (Sap+Syrup)/2.

As stated earlier, there are a long list of caveats and reasons why it could take even more sap before you get that first draw.

[DrTimPerkins]

At the inlet, you have raw sap. At the outlet,you have pure syrup boiled down at 40:1 or 32:1or...
The AVERAGE density in the pan is (Sap+Syrup)/2.

This approach is totally valid. I see nothing wrong with the calculation at all.

[TapTapTap]

Dr. Tim and others:

What exactly are you meaning by gradient? As I was thinking deeply on this thread, it occurred to me that we might use the term for any of the following:

- hydraulic surface gradient
- temperature gradient
- sugar gradient
- density gradient

All of them are related in some ways. The one outlier would might be hydraulic gradient since there are greater gradient changes at float boxes and other restricted areas. The other gradients might be generally constant across those funky hydraulic profile changes.

Ken

[DrTimPerkins]

I am referring to the density gradient, which is also a sugar (density) gradient, which affects temperature elevation, so is also a temperature gradient. I am ignoring all the other influences, like backpan/frontpan, number of channels, float boxes and heat distribution. While these are important in flow and density to some degree, they are too complex and varied to get into in this conversation, and don't really apply in how the gradient forms in most cases.

[Swingpure]

It will be my first time using a divided pan and I understand sweetening the pans and the gradient. I will have a 2x4/divided pan with four channels.

I figure it will take about 10 gallons to fill the pan to the 2” level when I am first starting off. (Maybe a little bit less). Not positive how many gallons required before the first draw off.

My questions is, how many gallons of sap should I have on hand, to make it practical to even start boiling for the first time?

Thanks

[wnybassman]

It will be my first time using a divided pan and I understand sweetening the pans and the gradient. I will have a 2x4/divided pan with four channels.

I figure it will take about 10 gallons to fill the pan to the 2” level when I am first starting off. (Maybe a little bit less). Not positive how many gallons required before the first draw off.

My questions is, how many gallons of sap should I have on hand, to make it practical to even start boiling for the first time?

Thanks

With a 18x60 raised flu I like to have 150 the first time. Usually gets it close to draw.

[berkshires]

It will be my first time using a divided pan and I understand sweetening the pans and the gradient. I will have a 2x4/divided pan with four channels.

I figure it will take about 10 gallons to fill the pan to the 2” level when I am first starting off. (Maybe a little bit less). Not positive how many gallons required before the first draw off.

My questions is, how many gallons of sap should I have on hand, to make it practical to even start boiling for the first time?

Thanks

If you have a divided flat pan that holds 10 gallons, and your sap is 3% on average, the math (as best as I can figure it) says you should be doing your first draw after adding about 150 gallons to the pan. That said, this same math tells me that on my 2x3 evaporator, running it at a shallow level where it only holds 15 quarts, I should start to draw after putting around 80 gallons on it. But experience tells me that I start to draw my first syrup after somewhere around 40-50 gallons put on it. I don't know if my math is wrong or if there's something I'm missing. But I'd expect you should start pulling your first syrup after somewhere between 80 and 120 gallons.

What I would say about boiling on a big flat pan for the first time is just to ensure you allow yourself enough sap, and enough time, for your boil _and_ your shut down. Don't feel like you necessarily need to get to that first draw the first time you fire up your evaporator, but make sure you have enough sap to last a few hours. If you're trying to get to that first draw and then you run out of sap after a couple of hours, and you're at a full boil, you are not going to be able to get that big pan off the evaporator. So watch out, as you can stop firing but it will keep boiling hard for quite some time. It would be a shame to scorch your pan the first time you fire it up. Ensure you have enough sap to keep feeding the pan for a while after you stop firing and your fire slowly dies and the pan slowly cools off.

Gabe

[Swingpure]

Thanks for the responses, they were helpful.

I will guard against running out of sap after I stop adding wood. I will learn after a few times, how much sap I need to leave in my 35 gallon feed tank to time that correctly. The goal is to have the feed tank near empty at the end of the day. I have a spigot on it and I don’t want to have to close it at the end of the day, so that it does not freeze closed. Right now my plan is to take it into the heated garage overnight to prevent that, but the preferred method is let it stay where it is, with the spigot opened.

I was also debating changing the float box setting near the end to allow the sap height to be a little greater as added protection.

I discovered last year that the first few days of collecting, I did not have high volumes so to get 50 or 100 or 150 gallons of sap could take a couple of days. Having 178 taps I’ll help with that problem.

Winter is returning today, ironically from a storm from the States. I think winter is here for good now. After the next five days of snow, I will walk all of the lines, to help keep a path going to the drops.

82 days until the Sugar Moon!

[DRoseum]

Have water on hand to feed into pans if necessary. A 5 gallon pail or two of "oh shoot" permeate can be a pan saver. Boiling out a bit more water the next time you fire up is WAY easier than dealing with a scorched pan!

[wnybassman]

Thanks for the responses, they were helpful.

I will guard against running out of sap after I stop adding wood. I will learn after a few times, how much sap I need to leave in my 35 gallon feed tank to time that correctly. The goal is to have the feed tank near empty at the end of the day. I have a spigot on it and I don’t want to have to close it at the end of the day, so that it does not freeze closed. Right now my plan is to take it into the heated garage overnight to prevent that, but the preferred method is let it stay where it is, with the spigot opened.

I was also debating changing the float box setting near the end to allow the sap height to be a little greater as added protection.

I discovered last year that the first few days of collecting, I did not have high volumes so to get 50 or 100 or 150 gallons of sap could take a couple of days. Having 178 taps I’ll help with that problem.

Winter is returning today, ironically from a storm from the States. I think winter is here for good now. After the next five days of snow, I will walk all of the lines, to help keep a path going to the drops.

82 days until the Sugar Moon!

Also will need to consider that anything that goes into the evaporator at the end should be brought to a boil to be able to go a period of time between boils. I switch over to straight pine with 8 to 10 gallons of sap left. This helps me get rid of any coals in the firebox so when it is ready to shut down, the fire dies quickly. When I get down to about 3 gallons left in the head tank I manually operate the float and drain it all into the back pan, I usually have near zero coals in the firebox by this time. I then shove a handful of finely split pine into the fire box and get a ripping fire going to bring the back pan to a boil. Once it boils, I stop with the firing and the fire dies out in minutes.

If you let sap trickle into the system at the end without boiling, you are introducing bacteria into a very sweet environment and things can spoil quickly. I have left the pans sit for a week in warmer conditions, and two weeks during cold snaps without (too) much worrying about spoilage.

[Swingpure]

Also will need to consider that anything that goes into the evaporator at the end should be brought to a boil to be able to go a period of time between boils. I switch over to straight pine with 8 to 10 gallons of sap left. This helps me get rid of any coals in the firebox so when it is ready to shut down, the fire dies quickly. When I get down to about 3 gallons left in the head tank I manually operate the float and drain it all into the back pan, I usually have near zero coals in the firebox by this time. I then shove a handful of finely split pine into the fire box and get a ripping fire going to bring the back pan to a boil. Once it boils, I stop with the firing and the fire dies out in minutes.

If you let sap trickle into the system at the end without boiling, you are introducing bacteria into a very sweet environment and things can spoil quickly. I have left the pans sit for a week in warmer conditions, and two weeks during cold snaps without (too) much worrying about spoilage.

Thanks for the tip.

I will be boiling everyday I have sap to boil. I will make sure that everything in the pan is boiled before I put the lid on it.

I was thinking near the end, instead of an inch and half to two inches of sap in the pan, I will progressively up it to 3” a little before I shut it down.

Based on your handle and website it seems we have another passion in common.

https://share.icloud.com/photos/076Vid7CvUJuA8WxkIzYT0Puw

[DRoseum]

Increasing depth mid boil will most likely have a negative effect on your gradient

[wnybassman]

Based on your handle and website it seems we have another passion in common.

https://share.icloud.com/photos/076Vid7CvUJuA8WxkIzYT0Puw

Yeah, another expensive hobby. :lol: