Newby is back with boiling questions.

[wmick]

Hi Folks
I haven't been hanging out here much, for a while... Good to be back. .....an of course, I'm back with some questions for the seasoned maple junkies...
2 years ago I built an evaporator and got a very last minute run with it, (outside in the pouring rain.).. So I really wasn't in the mood to do any fine tuning...
Last year, I had spine surgery, and wasn't allowed to work in the bush, so I just boiled a few buckets worth (that my wife and kids tapped for me) on a propane stove....

I got back at it this year. Turned a used 10x16 garden-shed into a shack.. and finally got to do a half decent boil on the new (home-made evaporator) ....
24 x 72, with a 2x4 drop-flue and a 2x2 syrup pan. (both with dividers for continuous flow..).
Boiled down about 265 gallons of sap this weekend, in about 24 hours... and had no luck in getting a consistent flow or gradient...
It seemed to me, like every time I opened up the door to add wood, I would lose some boil, temperature in the syrup pan would drop, levels would change and syrup would migrate...
I did not actually get syrup from the outlet until about 20 hours in... 3 gallons of syrup... so I think my pans are too sweet at this point, but not sure??...

1. I feel like maybe I am feeding the fire too infrequently, and creating my own fluctuations.. Maybe every 15 minutes or so... (certainly not on a timer) How often do you folks feed the fire? Is this likely to be my problem?
2. Based on my loose description of my setup.... How long after starting a fresh boil, would you expect to be drawing syrup?
3. Can anyone direct me to some information on the relationship between liquid depth and boiling rate?? I know shallower is better.... but cant seem to find any scientific explanation why?

Just a FYI, my sketch shows the syrup pan lower than the flue pan... this is not actually the case.... I raised the syrup to the same level, with no float between the pans.

Thanks - to anyone that takes the time to read or respond to my long-windedness...

198341983519836

[DRoseum]

Quick answer to you question about liquid depth and evaporation/boiling rate:

"It takes approximately 8.3 BTU to heat 1 gallon of water 1°F. The more sap you start with in your pan, the more BTUs will be needed to bring it to a boil and sustain it. However, the surface area and volumetric evaporation rate remain constant for a given surface area. Therefore the most fuel efficient approach will limit the number of BTUs required, hence boiling thiner layers of sap"

https://www.sugartree.run/p/sugaring-diy.html

[wmick]

Quick answer to you question about liquid depth and evaporation/boiling rate:

"It takes approximately 8.3 BTU to heat 1 gallon of water 1°F. The more sap you start with in your pan, the more BTUs will be needed to bring it to a boil and sustain it. However, the surface area and volumetric evaporation rate remain constant for a given surface area. Therefore the most fuel efficient approach will limit the number of BTUs required, hence boiling thiner layers of sap"

https://www.sugartree.run/p/sugaring-diy.html

Thanks DRoseum... I am a bit confused, yet... I do understand "8.3 BTU to heat 1 gallon of water 1°F". It's the "and sustain it" part that I'm not clear on. My question is specifically about throughput, after the system is boiling.
EG... Lets say pans are completely up to temperature and things are flowing.... All other factors being equal, would there be any difference in rate of evaporation (gph) between 1" of liquid in the pan vs 2" ?
....and if so, why?

[DRoseum]

Yes. At steady state, it's all about balance of heat in vs heat lost. The larger volume of sap (deeper in your pan) will have a greater heat loss from the sides than a thinner layer. This is because you have a far greater surface area around the outside of the pan exposed to ambient air temps. In your example of 1" vs. 2" you have double the surface area of heat loss thru the pan walls without gaining any evaporation surface area.

So you will need to be putting more heat in (e.g., BTUs) to sustain that boil. Therefore a less efficient evaporation rate per BTU.

Does that help?

[wmick]

Yep - That makes sense. Thanks.... and it did occur to me, but I just assumed that the extra inch of heat loss from the pan sides would be too insignificant to create a noticeable difference in throughput..

[BCPP]

1" around the perimeter of a 2x6 pan is about 1.6 sq ft so about a 10% increase on the 12 sq feet of pan area!

[Russell Lampron]

You are firing too infrequently. You should fire every 5 to 8 minutes depending the type of wood you are burning. With a natural draft you will probably get the best results with only 2 or 3 layers of wood in the firebox. I did with mine before I went with forced draft. Your wood should be split to about wrist size, no bigger. An evaporator that size should be boiling off about 25 to 30 gallons per hour and your only getting about 11 the way that you're doing it now.

[DRoseum]

Yeah and remember, in a continuous flow pan, you have the same amount of new sap coming in to offset what you are drawing off plus evaporating out and you have to heat that up too.

[bj's sugaring]

Fire quick and often, and make sure that the fire doesnt clog itself with those frequent firings. Keep your levels the same for now, until you get used to reacting to the faster evap rate.

[Trapper2]

Quick answer to you question about liquid depth and evaporation/boiling rate:

"It takes approximately 8.3 BTU to heat 1 gallon of water 1°F. The more sap you start with in your pan, the more BTUs will be needed to bring it to a boil and sustain it. However, the surface area and volumetric evaporation rate remain constant for a given surface area. Therefore the most fuel efficient approach will limit the number of BTUs required, hence boiling thiner layers of sap"

https://www.sugartree.run/p/sugaring-diy.html

I just read your complete article and found out I've been boiling incorrectly for 40 years. I usually start boiling at 4:00 pm on Fridays and continue straight thru until 10:00 am or so on Sundays. I don't do a draw off until then. I just keep on trickling sap in until that time. I'm using a 36X42 flat pan. I cant imagine syrup much lighter in color than this.
19840

[DRoseum]

That syrup looks great! If its working for you, I wouldn't change a thing!

Its really not right or wrong per se, just different technique. For large flat pan you might be fine. But boiling in tall pot with a lot of sap and limited steam surface area could lead to the localized burning of some of that sugar that was in there from the start.

[wmick]

Well.... I did another run on the weekend... and unfortunately it took me until the last 3 hours.... but I think I finally figured out, a little better, how to run this thing... I have some theories, at least.. As I've never actually helped an experienced sugarer run an evaporator, I am really learning from my mistakes and theories..

Started to boil at about 10:30 pm on Friday.... Steady firings 8 minutes apart... Good boil in the flue pan, and semi-decent boil in the back two sections of the syrup pan, but not so much in the front section by the draw off. Temperature in that last section seemed to hover around 215 degrees for ever.... just couldn't seem to hit the 219. Several tests with the hydrometer confirmed that I did not have syrup...Dad came and took over at about 9:00 AM, so I could have a nap. He was able to draw off about 2 gallons early afternoon, Saturday, and then that draw off section seemed to cool down again. About 6 PM, still no more syrup... and I could see that my sap tank would be empty within 3 or 4 hours, I tried something different... I started feeding as much wood to that fire as I possibly could (without snuffing it)... Much hotter fire than I'd been doing all along... and things started to happen... Temp came up at the draw off and I started drawing a drizzle of syrup at about 7 PM, and did not close the valve until about 11:30pm, after I let the fire go, due to lack of raw sap in the tank....
I ended up with about 15 gallons of very dark syrup... Good tasting, and clear of niter... but very dark.

I believe my biggest mistake was my "slow and steady" approach with the fire.... Even though it seemed like a good consistent boil, I think I was not accommodating the introduction of enough fresh sap to push things through at the capacity of the evaporator... and I basically was allowing things to simmer, and overcook too early in the system... (and allowing dense and light product to migrate back and forth throughout the pans.). I need to get it through my head that this is not a wood stove... and wood consumption should not be a concern.:)

Sap has slowed down here a lot..... but with any luck, we might get a decent run or two this week, and I'll be able to give the boil one more try this year. A RO home-build is definitely in order for this year, as I am getting way too old for the all-nighters and 36 hour shifts.:emb:

PS.. I'm wondering... Would it make any sense at all, to start a small trickle from the draw-off early in the boil? (even thought it's not syrup yet)... Just to simulate the end result of flow, and get things "moving" ?? Is this a thing?

Thanks

[Big_Eddy]

I just read your complete article and found out I've been boiling incorrectly for 40 years. I usually start boiling at 4:00 pm on Fridays and continue straight thru until 10:00 am or so on Sundays. I don't do a draw off until then. I just keep on trickling sap in until that time. I'm using a 36X42 flat pan. I cant imagine syrup much lighter in color than this.
19840
Don't sweat it - seems there are a lot of us experienced sugarmakers have no idea how syrup "should" be made. lol

[Sugarmaker]

wmick,
Fire it like your neighbor is buying the wood! We fire every 10 minutes on our rig. Wood fires are the toughest to control and keep a steady boil. I dont think there is any advantage in starting to draw off syrup before its syrup. Your just going to have "light" less dense syrup that needs to be boiled more or mixed with heavy syrup.
You mentioned something that always concerns me on these types of rigs. I dont agree with the draw off port in the front corner, which is probably the coldest part of the evaporator. Your increased firing rate and wood near the front allowed this front partition to start to come up to temp and made syrup at that point. (you noted the better boil in the back portions of the syrup pan, Yea thats where the syrup should be made! But your rig is set and if you keep fire under it long enough you have to make it in to syrup.)
ea these are not wood stoves these are wood eaters! You should have a rolling boil in all the partitions. Keep boiling!
One other thing. You did or do have niter in the syrup. I dont think I have ever heard of syrup being made without niter. If you have some in a glass jar it should settle to the bottom or maybe I missed the part about you filtering it??
I think your doing good as a start up. Actually a pretty good set up! After you had the pan sweet the hot fire made syrup sooner than before. Sounds about right.
Regards,
Chris

[wmick]

Thanks Chris - I also wondered about the location of the draw off... I fashioned the design after stuff I found on line... but with recent experience and reading comments like "syrup should be made at the hottest spot on the evaporator",,, and comments like yours... Im thinking maybe I should modify for next year... Maybe go from the flue pan to the front of the syrup pan, and work back to a draw off in the back section ?? or, turn the pan 90 degrees and run longitudinally like the flue pan... This way, all three sections would get some good heat, at the back end. Any thoughts?


As for the niter comment... Yes - Lots of niter, before filtering it out... I was referring to the syrup in the jar, after filtering and hot-packing... I had a more successful filter/bottling process this year, than some previous.. Learn a little bit every year... Unfortunately its a long wait between seasons to try out new ideas...

[wmick]

Anyone Care to Weigh in? Whats your favourite?
Thanks

19932

[Buddy 58]

Option 3 , even heat across , gradient left to right .

[ecolbeck]

Option 2. If the back of the syrup pan is the hottest spot, then near syrup should spend the most time in that section.

[RileySugarbush]

Option 2, Similar to my 2x8 from Smoky Lake. Works great.

[mol1jb]

Option 3 with the extra partition will make establishing gradient even easier. I have a syrup pan identical to option 3 and it works great.

[wmick]

I appreciate the insight... Thanks.
I find it interesting, that with such an ancient art... there is still lots of room for theorizing and creativity.
Sure hope we get a few more votes though.... Tied up at two at the moment...

Fingers crossed that I might get enough sap to try one more boil this weekend...
Pretty sure I could pull off a pan modification between now and then...:cool:

[Russell Lampron]

Option 3 works for me. My front pan is set up like that but I have draw off/float boxes on my pan and I just swap the float from one side to the other when I want to change sides.

[Super Sapper]

I vote option 2, this will get the draw off channel over the hottest part of the evaporator. Running the other way you have a larger portion of your last channel sitting on the rail reducing heat transfer.

[Big_Eddy]

Mine is option 1. My last channel boils just a bit softer than the middle syrup channel, but I like that because it makes the whole evaporator less touchy. I never make syrup anywhere other than the last channel. I run pretty shallow (3/4") if I'm just boiling. A little deeper on a "work" from home day.

Looks like you now have some of all versions covered.

[wmick]

Anyone Care to Weigh in? Whats your favourite?
Thanks

19932

#2 or #3 were my picks... As the response was not overwhelmingly weighted in any one direction, I'm going to take a chance on #3. A quicker and easier modification for me, as I wont need to change my pan-to-pan pipe, which has special milk-line fittings. I just need to add a couple 1/2" fittings for my thermometer and the draw off valve... and tack in some new dividers.... Should be quick.
Will let you know how things work out... It will be nip and tuck, whether I have enough sap to start a fresh run this weekend..
Thanks Again

[Sugarmaker]

I like both these and both should work and maybe even a little better than the current front corner draw off. depending on your pan construction and ease of changes could determine which way to go. Good luck!
Regards,
Chris

[wmick]

Just a little update.... Maybe not so little.:)
Did my last boil for this year... Roughly 1900L in 24 hours... so about 80L or 21 Gallons / Hr. I’m fairly happy with that... I know I could do better if I had better more consistent and smaller split wood... I burn a mixed bag of dead fall and culled trees.

Started up about 8AM Saturday, with clean pans and about 2/3 of the sweet from my previous run. I had finished off some of it, thinking I was done for the year, but changed my mind.... I poured the partially boiled sap into the syrup pan from the front, while the fresh sap was pouring in from the back end, attempting to simulate the gradient a bit... Not knowing the density of my mix, I was guessing at how long it might take to sweeten the pans.

I went with #3 modification on my syrup pan... and I was much happier with how the pan worked... All 4 sections had a nice rolling boil. I think that's a good thing.

I learned that my hydrometer does work. (after the fact), but seems like too slow of a process to check for syrup when the thermometer spikes to 219 in a hurry.

My temperature at the draw off went above boiling point fairly early in the run.... but it just hung out at about 216 forever??... I couldn’t seem to get it past that point.. And, Yes – I did check the calibration on my thermometer. At about 19 hours in, it quickly rose to the 219 and all hell broke loose... I had a hard time keeping the temperature down at 219... Drawing off as much as I could... The Level in the syrup pan was dropping.. and the pan seemed to be more air/foam than liquid... I was choking the fire to try and settle things down.. We survived it with no casualties except for about 18L of over-dense syrup... (all in one draw !!). Then it cooled down for a while. At about 23 hours, it happened again... except this time I was a little more prepared for it... and choked the draft back a bit right away. This, again, was approximately 18L drawn off in one quick batch. And this time I discovered a new problem..

The level in my float box was dropping slowly while I was drawing off. This likely could have attributed to the foaming/dropping issue I had the first time.... I overcame it by propping the float valve wide open.. and it was able to just maintain the level. Apparently I need some bigger lines and fittings from my tank to make up for a lack of head pressure when my tank level gets near the bottom.

So – all in all, this run produced about 36 L of syrup from the draw off,,,, and I kept about 40L of the densest sap from the pans for the turkey cooker.

I am somewhat frustrated that I haven’t figured out how to make this thing “Flow”, like I think it should… with a constant trickle at the draw off, rather than these periodic large batches… Oh well… I have 11 months to think about It… I’m sure I will learn a little more every year.. and with any luck, I will add a RO home-build to my list of complications by next…

This reasonably new hobby of mine scratches a couple itches. Great excuse to spend some time out in the bush in the non-hunting season…. My need to experiment, develop, build and improve machines and processes. And my love to share a harvest with family and friends. I sure couldn’t do it without the help and experience from you folks on this forum… What a great community. Hope you all had/are having a great season… Best of Luck.

[Sugarmaker]

wmick,
Doesn't sound like you did any thing wrong. I need to back and look at concept #3. Yes concept #3 should be good set up. You have been busy! Question did you completely seal all the partition seams to keep sap from mixing???
My guess is that your still kind of making syrup in a batch mode. My rig does that all the time. First draw is big. Then they get smaller and more controllable as time goes on in the boil but I rarely get a trickle beyond maybe 30 seconds when it has finally got all the big batch of syrup out of the system. Those initial large batches are somewhat common. It may never do a continuous flow. The term is more of a concept than a reality. The syrup is holding near the draw off until it gets up to temp. If the bubbles show that you have syrup a lot farther back in the system then the batch will be large and or the draw off temp may rise. You might try drawing off a full degree or more under temp for that initial large draw of syrup then check density and continue to adjust the set point temp as the draws get smaller and more frequent.
Just my 2 cents.
Regards,
Chris

[ennismaple]

With an elevated sap tank your flow through the float box will be higher (deeper sap depth in the pan) when the tank is full vs when the tank is nearly empty. We always need to adjust the float box as the levels drop in the head tank.

Do you have a float between your flue pan and your syrup pan? If it is just a partially open submerged valve you can get mixing back and forth which will kill your gradient. Most commercial evaporators have a float between the pans to prevent backflow and allow you manage different levels in your pans. We run 1" above the flues but 2" deep in the front pan but the sap drops about 6" as it enters the front pan.

[wmick]

wmick,
Doesn't sound like you did any thing wrong. I need to back and look at concept #3. Yes concept #3 should be good set up. You have been busy! Question did you completely seal all the partition seams to keep sap from mixing???
My guess is that your still kind of making syrup in a batch mode. My rig does that all the time. First draw is big. Then they get smaller and more controllable as time goes on in the boil but I rarely get a trickle beyond maybe 30 seconds when it has finally got all the big batch of syrup out of the system. Those initial large batches are somewhat common. It may never do a continuous flow. The term is more of a concept than a reality. The syrup is holding near the draw off until it gets up to temp. If the bubbles show that you have syrup a lot farther back in the system then the batch will be large and or the draw off temp may rise. You might try drawing off a full degree or more under temp for that initial large draw of syrup then check density and continue to adjust the set point temp as the draws get smaller and more frequent.
Just my 2 cents.
Regards,
Chris
Thanks Chris
No I did not completely seal around the dividers. They are just tacked in... This never occurred to me that this might be an important piece.... .. I can certainly seal them up for next year and eliminate one potential contributor. I certainly hope I can make some improvement to the flow/frequency... I would find it much more relaxing than waiting hours for the ensuing chaos... Unfortunate to wait for a year to test more ideas... however, I guess that's what makes it a treat.
Thanks for your help.

[wmick]

With an elevated sap tank your flow through the float box will be higher (deeper sap depth in the pan) when the tank is full vs when the tank is nearly empty. We always need to adjust the float box as the levels drop in the head tank.

Do you have a float between your flue pan and your syrup pan? If it is just a partially open submerged valve you can get mixing back and forth which will kill your gradient. Most commercial evaporators have a float between the pans to prevent backflow and allow you manage different levels in your pans. We run 1" above the flues but 2" deep in the front pan but the sap drops about 6" as it enters the front pan.

I don't have a float between the pans.. When I built the Arch, it was my intention that the syrup pan could sit about 1.5" lower than the flue pan, with a float in between... but someone talked me into just leveling up the 2 pans..., so I just added an extension ring under the syrup pan.
I am open to trying the float idea... It would be a bit of work, but not out of the question. After boiling on it, I'm fairly certain that I would need much more than 1.5 "drop" between pans to keep the float box fed and working properly... (closer to your 6" likely) Definitely something to think about.. I do like the idea of back-flow prevention, and separate pan depth control. But then again... Just a couple more things for me to mess around with. Will give this some serious thought.
Thanks

[ennismaple]

Once the float between the flue pan and the syrup pan is set you never touch it for the day. Yes - you keep an eye on it but given the fluid levels between pans stays relatively constant (vs the falling head in the sap tank that feeds the flue pan) you set it and forget it.

As long as the end of the pipe that joins the flue pan to your syrup pan is above the fluid level in the syrup pan you can control the flow using a simple valve. It prevents backflow but is more work to maintain constant levels.

[Sugarmaker]

wmick,
I believe most drop flue or flat pan systems are set at same level. Float box may work but not sure its necessary between pans? May need more info on that. But I am pretty sure that you wont be able to get a good gradient going in the syrup pan if it is leaking from one partition to the next. If leaking, its just like one big open pan and you can make syrup, but the batches will be much larger and take longer to get to syrup. Which kind of sounds like your last boils.
Regards,
Chris

[Big_Eddy]

wmick - I've read through the thread again and I can't find where you tell us what depth you are actually boiling at. It makes a big difference in the "flow" through the evaporator.

If you are running at 2", then your draws will be larger, and further apart than if you are running at 1" for instance. Much more than twice as large and twice as long between.
Running shallow drastically reduces the intermixing within your pans and therefore the gradient is "steeper" between sections of your pan.

However running shallow even more drastically increases the risk of running dry and burning pans, either due to a fast transition from almost syrup to smoke, or the inability to replenish sap fast enough. If your float pan or interconnecting pipes are not right at the bottom of the pans, or too small, this becomes even more of an issue. I have 1" pipes connecting my pans, and if I am trying to run at 1" and boil hard then the depth in the flue pan drops to about 1/2", and very little sap is able to flow forward to the syrup pan through that 1" pipe. Makes for some excitement when drawing off, if nothing is flowing forward to replace the drawn off liquid.

You're going to take a few goes before you get a real feel for your setup, but you seem to have a good setup and a good understanding - now you just need more sap to play with . (don't we all!!)

[wmick]

wmick - I've read through the thread again and I can't find where you tell us what depth you are actually boiling at. It makes a big difference in the "flow" through the evaporator.

If you are running at 2", then your draws will be larger, and further apart than if you are running at 1" for instance. Much more than twice as large and twice as long between.
Running shallow drastically reduces the intermixing within your pans and therefore the gradient is "steeper" between sections of your pan.

However running shallow even more drastically increases the risk of running dry and burning pans, either due to a fast transition from almost syrup to smoke, or the inability to replenish sap fast enough. If your float pan or interconnecting pipes are not right at the bottom of the pans, or too small, this becomes even more of an issue. I have 1" pipes connecting my pans, and if I am trying to run at 1" and boil hard then the depth in the flue pan drops to about 1/2", and very little sap is able to flow forward to the syrup pan through that 1" pipe. Makes for some excitement when drawing off, if nothing is flowing forward to replace the drawn off liquid.

You're going to take a few goes before you get a real feel for your setup, but you seem to have a good setup and a good understanding - now you just need more sap to play with . (don't we all!!)

I've tried different depths.... This last boil I had it at approximately 1.5" at the float box... which is deeper than I'd like for the flue pan.... but I've had some close calls up in the syrup pan when I try to run shallower... When things get hot, I'd say I'm at about 1" in the syrup pan. Even at this setting... when things get roaring to the drawing off stage, my level in the syrup pan goes down to the point my thermometer almost sees air (its about 1/4"" off the bottom) and the flow from my draw off valve almost stops... (its right at the bottom of the pan) ... Very Scary.
I up-sized to 1.5" pipe between the pans this year.... as it was way too small before (1/2" :o)... I am going to increase the size of all my fittings for next year... Draw-Off, tank to float and float to pan,... Try to take all the flow restrictions out of the mix...
Yep - Unfortunate to be out of sap.... but then again, just in the nick of time for my marriage to survive for while longer.... (till hunting season, anyway)
Thanks for the tips.

[PaulRenaud]

I have a 2x6 setup that I run with about an inch in the evaporator and 1/2 to 3/4 inch depth in finishing pan. Am able to start a trickle when I draw off and don't seem to have a problem pushing the syrup along between the pans. I use a hydrometer to check when to draw off.

But my question is how do I know when the syrup that I am drawing off drops below the target brix level so that I should stop the draw? Sure I can constantly take a sample and check with the hydrometer, but is there a way of telling visually? Thanks.

[mainebackswoodssyrup]

You’ll have to check it manually on when to close the valve.. The only other way is to purchase an auto drawoff. We have one for our 2x6 and love it.

[Russell Lampron]

But my question is how do I know when the syrup that I am drawing off drops below the target brix level so that I should stop the draw? Sure I can constantly take a sample and check with the hydrometer, but is there a way of telling visually? Thanks.

Do you have a thermometer near the draw off in your pan? Watch the temperature at the draw off and open and close the draw off valve as the temperature fluctuates.

[30AcreWoods]

If you don't have a horizontal probe near your draw off valve, you could clip a digital thermometer on the side of your pan at the valve location. Just use one of the apps online that will tell you the appropriate compensated temperature for syrup at your location on any given day (altitude, pressure, etc.). Once things get moving nicely, you should be able to crack the valve just a bit and maintain a relatively continuous flow. This will allow you to boil sap to syrup in the minimum possible time - which might change your grades.