Air injection Front or Back Pan

[lew]

I am considering building an air injection/bubbler for my 5x16. I have seen units with the bubbler in the flue pan and the syrup pan, and I have seen units with the bubbler just in the flue pan, but not the syrup pan. I haven't seen a bubbler in just the syrup pan and not the flue pan, they may exist, but I haven't seen one. My question is, would it be effective to just put the bubbler in the syrup pan and not the flue pan? I raise this question because I would like to try one, but installing it into my Leader Max Flue pan looks to be a difficult task because of all of the cross bracing welded to the top of the flues. If it would be effective to have it in just the front pan, then not only would it be an easier build, but also cheaper. Anybody out there have any experience with a syrup pan only bubbler?

[DrTimPerkins]

The effectiveness of the air injection system (in terms of making lighter syrup) would be greatly diminished if it were not placed in the flue pan.

[lew]

Ugh! Thanks

[Mark]

I wouldn't try putting bubblers in a deep flue anyway. I know of one person having problems with the welds cracking on the ends of the flues. Pump too much air in a deep narrow flue you might have some temporary dry spots that heat then cool when the sap hits it again.

If you decide to try putting them in the flue pan you could make the tubes come up over the brace and back down. I have braces on the side flues on mine and the tubes come up over the brace and back down. Just no holes drilled in the part that comes up over the brace.

This year I pulled the bubblers near the end of the season trying to make some dark syrup, customers don't want the light stuff. The reason I like them is I don't have to use any defoamer unless I am boiling real hard with dry chips. A little organic defoamer works with the bubblers in that situation.

[lew]

Been thinking about this a little more, and came up with, Why does the tube have to be in the bottom of the flue? Why can't it be on top? Yes, you would get better mixing if it were in the bottom of the flue, but the actually boiling sap is providing a great deal of mixing isn't it? Thoughts?

[DrTimPerkins]

Been thinking about this a little more, and came up with, Why does the tube have to be in the bottom of the flue? Why can't it be on top? Yes, you would get better mixing if it were in the bottom of the flue, but the actually boiling sap is providing a great deal of mixing isn't it? Thoughts?

Those of us at UVM PMRC believe that air injection works (to produce lighter syrup) by rapidly cooling the liquid below the activation energy for invert sugar to caramelize (darken and form flavor). Evaporation rate is slightly depressed if you use air injection. If the cooling doesn't occur very quickly, then some degree of caramelization will still occur. Will it work to still make syrup lighter....yes, probably to some degree. Will it be as efficient as placing them low in the flues (but not tight against the flues), probably not nearly as well.

An analogy to air injection might be like toasting a marshmellow over a fire. You are constantly right on the edge of the thing burning. If you aren't careful, then you start to burn it and once it starts the whole thing often burns. If you're very careful and keep turning it to prevent any part of the surface from getting too hot you might be able to just lightly toast it without it burning, but this is extremely difficult to do. Air injection would be sort of like constantly blowing on the marshmellow while it is over the fire to keep the temperature on the surface from ever getting hot enough to burn and char. With your thought of putting it further away, although you're likely to help prevent charring somewhat, the marshmellow would still be likely to be darker than if you blew on it more vigorously and closer. How far away is OK is difficult to determine. Put it far enough away and you can blow all you want and the thing still catches on fire and burns, but if it is close enough it might help some. I would imagine a good amount of experimentation would be needed to get it to work well...compared to the standard method of just putting the tubes down into the flues (but again, not tight against them).

For completeness sake I should mention that there are others that believe that air injection works via some sort of chemical oxidation process (bleaching of color bodies that have already formed by all the extra oxygen in the air being injected). If that is the case (I find the arguments for that mode of action to be very unconvincing) , then you would still get lightening of the syrup in your design, although perhaps not quite as much.