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Maintaining Gradient While Boiling

May 10, 2021

Here are some important points to consider when operating a continuous flow evaporator. “Continuous flow” means the pan(s) contain(s) dividers.

  • Sap must be introduced slow and steady. For best gradient, it is best to NOT pour sap in by hand. There must be a steady flow of sap entering the pan to replace the vapor that is leaving the pan via evaporation. Incoming sap must also responsively replace syrup as it’s being drawn off.
  • Sap depth in the pan must be absolutely consistent. Fluctuations in sap depth will mix the contents of the pan.
  • Sap must be kept at a reasonably low depth.  The deeper the liquid depth of the pan, the longer it will take to establish a clear density gradient and the more time that must be spent reaching subsequent draw-offs. 2″ is a good, safe starting point. As you gain familiarity and confidence with the process and the evaporator has stabilized during a processing session, slightly lower depths can offer enhanced performance.
  • NEVER NEVER EVER, play around in the pan with a scoop or a skimmer. If someone is scooping foam off or trying to net bugs out of the sap, you may as well use an open flat pan.  If anyone is standing near the evaporator holding any instrument which they intend to dip into the pan, they are an advocate for your frustrations.
  • When drawing syrup off, twist the handle of the valve slightly as to release a slow and steady stream of syrup. By opening the valve fully, you will struggle to maintain depth and will inevitably mix the contents of the pan as fresh sap eventually floods in to replace the high volume of syrup which was removed.
  • Keep foam under control.  Do this by periodically adding a SINGLE drop of vegetable oil to the pan. NEVER mechanically remove foam by any means.
  • Fire consistently.  When using a wood-fired evaporator, maintaining a regular firing schedule is nearly as important and consistency in sap introduction; and they work hand in hand.  If a fire dies down too far and takes even a moment to revive, too much mixing is allowed to occur due to the consequential lack of incoming sap or fluctuation in sap depth.
  • Fire well. Don’t feed your evaporator poor fuel and expect favorable results. The higher the evaporation rate, the faster the sap moves through, the stronger the gradient, the faster and more often you get syrup drawn off, the higher the grade of syrup.
  • Sap must be introduced in the corner opposite of where syrup is to be draw off. This may sound elementary, but the longer the distance between “sap in” and “syrup out”, the stronger the density gradient will be.
  • Keep the pan level. Levelness is less important than any of the points listed above this point, but it is still something that is easy to maintain and will help create positive gradient and provide safety for the pan while under fire.
  • Test the sugar density of your sap. Sap less than 1.5% sugar is sometimes better to be boiled as a batch than trying to establish a gradient with it.

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