First Evaporator - End of Boil Techniques

[Kubota]

I'm a small scale hobby setup with maybe 50-60 taps this year. It's my first year with an actual evaporator (WF Mason 2x3), which I'm looking forward to very much. I Batch boiled last year on a barrel evap.

I'm wondering how most people finish their boils. I'll mostly boil Friday through Sunday. In a continuous flow setup, do you leave the pan "sweetened" all season and never really drain (except to maybe clean)? Or do you empty the pan after each weekend?

Leaving it sweetened would be a million times easier. i'd imagine it's just crucial to make sure you leave enough sap to keep the pan full during the cool down stage. Then start right back up where you left off. I'd imagine the pan would never sit for more than 4 days without being fired.

It would be much harder to empty the pan each time. Plus there would be +/- 8 gallons of a syrup/sap filled pan that I would need to finish boiling down on an alternate heat source. Most likely a propane burner.

I have also heard of pushing out the end of the pan syrup through with water. This still results in a complete start from scratch each boil.

What do most of you guys do? Syrup is just for personal use and giving to friends/family.

Thanks,
Mike

[maple flats]

I leave it sweetened from first boil until the end of the season with some exceptions. 1. To clean the pan I drain it into my draw off tank, then clean the pan, then pump the concentrate back into the pan. 2. If I did not have enough sap to boil hard at least 3- 4 hrs and temperatures are forecast to be above 40F or below about 15F I drain it and store it in a cool but not warm location.
Once boiled 3-4 hrs you should have enough sugar in the concentrate to keep it from freezing, it may form slush on top, but not freeze solid to hurt the pan. In my early days if I doubted the safety of letting it set, I used to put a 40 watt bulb in the firebox. The heat from that even kept slush from forming, I have not done that in likely 15 years. The main thing is to have enough sap on your first boil to last at least 3 or 4 hrs. Your 2x3 should evaporate 5-7 gal/hr thus you want 15+ gal of sap.
I always cover all of my pans when I shut down, to prevent anything from getting into the pan with the concentrate.

[DrTimPerkins]

People use both approaches (leave the sweet or empty/finish in another container). Whatever works best for you. Note that if it is warm, you'll need to fire up every couple of days to boil briefly to prevent the sweet from spoiling (going ropey), so you either need to leave plenty of sweet in the pan for that, or add water.

"Pushing the sweet" does not fully empty the sugar from the pan -- far from it, especially if you're starting with sap rather than concentrate. It only steepens the density gradient and allows you to get a little more syrup out (that's a concept that is a little too complex to get into in a quick reply). There is still a considerable amount of sugar left in the pan afterward.

[Kubota]

Awesome stuff! Thanks for the responses.

Looks like I will make every effort to try to keep the pan sweetened as much as possible. Great suggestion to just empty the pan and pour it right back in on the next boil, I didn't think of that, but that's a great idea.

Interesting points on pushing out with water. This was likely my last resort, but I think I'll definitely avoid this method now.

[DrTimPerkins]

Interesting points on pushing out with water. This was likely my last resort, but I think I'll definitely avoid this method now.

Pushing sweet is more effective the higher the evaporator incoming concentration. Essentially what you are doing is changing the steepness of the density gradient in the evaporator. Take a look at the figure below.

densitygradient.JPG

The red line is the gradient you'd get boiling sap (incoming evap feed of 2 Brix and syrup density of 66.5 Brix). We'll assume a steady, uniform change from feed to drawoff (although it can vary somewhat depending upon size, style, and configuration of evaporator).

Now, to push the sweet you would introduce water into the evaporator feed line. That would (eventually) change the density gradient to what is shown in the blue line. The extra syrup (sugar) you will push out is the amount shown by the "slice" in between those two line. As you can see, with sap/water it is very small.

So let's say you are using concentrate at 8 Brix. That is the green line. The "slice" between the green (concentrate) and blue (water) lines is much bigger. Similarly, if we increase the concentration level to 20 Brix (yellow), the "slice" of sugar you'll get out of the evaporator by "pushing the sweet" will be correspondingly larger.

Regardless, you will never get all the sugar out no matter how much water you "push" with. You cannot lower the drawoff side of the line (unless you drop the syrup density), so after a while all you're doing is boiling water and will get no further drawoffs.

So "pushing the sweet", although used frequently, is actually a misnomer. The more proper term is "steepening the density gradient" to get more sugar out of the pans.

An alternative, if you have a system with a front and back pan, is to boil until you are out of sap or concentrate, then close the connection and transfer all the sweet from the backpan to the frontpan (it might be pretty deep to start with), and boil with water going into the backpan. Shut off the drawoff and boil until the entire frontpan is syrup. You should ladle the syrup around during the boil to make sure it is homogenous. This is how we typically finish up at the end of the season.

[snoskier16]

An alternative, if you have a system with a front and back pan, is to boil until you are out of sap or concentrate, then close the connection and transfer all the sweet from the backpan to the frontpan (it might be pretty deep to start with), and boil with water going into the backpan. Shut off the drawoff and boil until the entire frontpan is syrup. You should ladle the syrup around during the boil to make sure it is homogenous. This is how we typically finish up at the end of the season.

This is something that I know I'd run into and have to figure out later in the season, so having it explained completely should make things a bit less stressful in the moment!

I'm thinking that you do the transfer from pan to pan while the evaporator is cold, correct? Doing it with everything fired up seems like a really good way to scorch a pan!

[DrTimPerkins]

I'm thinking that you do the transfer from pan to pan while the evaporator is cold, correct? Doing it with everything fired up seems like a really good way to scorch a pan!

Yes. Shut it down for a little while to cool, shut off the connection between the pans, transfer the sweet from back pan to front, flood the back pan with water, then fire up again. Keep water/permeate flowing into the backpan while boiling. No need to drawoff until the entire front pan is syrup. If you go a little over density, add water to the front.

[berkshires]

Great info here! I'm in a similar boat to the original poster. Like him, I've always batch boiled before, and this will be my first season with a divided pan. Like him, too, I'll only be boiling weekends. And in my case that's a pretty hard rule because my sugar shack is nearly a two hour drive from my home, and I work full time. So I really can only boil on weekends.

I think early season when it's cold all week, I can just drain my pre-heater into the pan about an hour before the boil ends. Then I should be able to let the sweet stay there for the week with nice cold nights.

Later in the season when it's warm I'll need to drain the pan every time. I'm thinking it will go something like this:
- Drain the pre-heater into the pan (same as above) and boil for a bit before shutting down.
- Drain the pan into a container (or containers) that I'll take home, and then bring back the next week.

For that second step, I'm thinking it might make sense to drain the pan into three containers.
Container 1: The first draw-off. This should be dense enough that I can probably finish it at home on the stove.
Container 2: The second draw off. Somewhat sweet. This will go in the chest freezer at home for the week.
Container 3: The last drawoff - everything that's left in the pan (will also go in the chest freezer)

So here's a question: When I go back to the sugar shack, could I start off with a gradient in my evaporator if I take container 2 and empty it into the pan. Then take container 3 and pour it in slowly at the sap end. And then add raw sap?

What do you think Dr Tim? Should that work?

Thanks!

[DrTimPerkins]

So here's a question: When I go back to the sugar shack, could I start off with a gradient in my evaporator if I take container 2 and empty it into the pan. Then take container 3 and pour it in slowly at the sap end. And then add raw sap?

That should help establish the gradient a little faster (assuming nothing is frozen solid of course). It is similar to what we do when we clean (or change) pans. We put the frontpan contents in one container and the backpan contents in another. After cleaning we'll put them back in the appropriate location, start the concentrate flow into the evaporator, and commence boiling.

As far as storing the contents....if we aren't boiling for a while and need to clean, we will put the sweet from the front and back pans (separately) into drawoff containers while still really hot, and cover them up. Haven't had any problems for up to a week that way (in cool weather), although our backpan sweet is typically around 40 Brix already and the front about 55 Brix. If we aren't cleaning, we'll leave it in the pans (uncovered) and boil briefly every 2-3 days.

[RedMapleCreek]

I also have a Mason 2x3 and have learned a lot operating it over the past 4 seasons and have evolved my procedures accordingly. I now usually run it at a depth of 3/4" to 1" and can get 8 gal/hr evaporation rate by firing about every 6 minutes with dry wrist size hemlock. Wrist size hemlock was recommended by Bill Mason as the best fuel when we bought the evaporator. Note there is only 3.75 gal in the pan at a 1" depth. Running it this shallow you do have to stay on top of it, but any deeper and your evaporation rate drops off significantly. You shouldn't run it this shallow at first until you develop a feel for it. When I shutdown, after it has cooled there is usually just under 1/2" in the pan since it continues to evaporate as the fire box cools. Be careful with your shutdown to make sure you have enough sap to keep the pan from drying out as your evaporator cools down from your last firing.

If I am going to be boiling the next day I just leave it as is and cover it with a 2x3 ft sheet of aluminum once it has cooled. It can stay like this for a few days if the weather doesn't get too warm. If it will be too warm or I will not be boiling again soon I drain the sweet into a food grade bucket and store in a snow bank or into large mason jars and store in the fridge or a cooler with ice or snow. The best time to drain it is after it has cooled down so that the sweet is still warm enough to flow nicely (about room temperature). The Mason 2x3 is small enough that it is relatively easy to completely drain by elevating one side with a couple of blocks and then lifting it a little end to end to get the flow going thru the channels. If there is a lot of niter after draining the sweet, it is easy to flush that out by chasing it along with water.