Quote Originally Posted by DrTimPerkins View Post
If you want more information on it, that is exactly the subject of the papers at http://www.uvm.edu/~pmrc/aging.pdf and http://www.uvm.edu/~pmrc/tubing_age.pdf The story is slightly different (more exaggerated) with 3/16" tubing due to the increased susceptibility (in some ways) to backflow-related sanitation issues.

In essence, the spout is the most important component to keep clean, the dropline next (unless you are using CV spouts/adapters), and the lateral line and mainline are really not at all important in terms of sanitation-related yield concerns. What it all boils down to is that the cleanliness of the spout is of primary importance because most of the contamination of the taphole is related to the spout due to very small perturbations in vacuum causing periodic movement of sap backward from the spout/tubing into the taphole (backflow). Of secondary importance is the dropline, because, more rarely, larger leaks or system shutdowns can result in sap moving from a few feet away back into the taphole. This is less frequent though, so the dropline sanitation level is less critical, but still important. It is very rare for sap to flow from the lateral line (or mainline) all the way back into the taphole, so sanitation level there is not really important (in terms of sap yield reductions). Thus changing spouts annually and droplines periodically (every 2-3 yrs), or using CV spouts/adapters (which negates the need to change droplines as often) will result in the highest yields.

With 3/16" systems, the problem does extend a bit further along, so lateral line sanitation is somewhat more important.

It's a bit funny to me, but fulfilling as well, to hear people talk about this so much like it is common knowledge. Ten years ago it was not the case. It took quite a number of years of research and quite a bit of grant funding, and a lot of papers and presentations to get to where we are. I've spent a good deal of my career looking at this stuff, but have seen the industry go from talking about good yields being 0.3 gal syrup/tap to now over 0.5 gal/tap or higher (the UVM PMRC average from 2004-2017 is 0.59 gal/tap).

More on the subject of sanitation at http://www.uvm.edu/~pmrc/?Page=checkvalves.htm and others under "Recent Publications" at http://www.uvm.edu/pmrc
Tim, you brought up a thing that has refreshed my memory yet again. That being, at least once or twice per season, if not up to 1/2 dozen times, I have had the mainline fill up. freeze, and the whole system backs up to the point where many drops fill up all the way back to the tap. In one of my bushes especially, most of the large mainline is located in the coolest part of the woods, in the valley, while the tress and lats are on southerly slopes, up higher. For example. Last spring....I was tapping during a heavy run day (and lost it all), by 2 oclock in the morning when I finished tapping, the weather had turned below freezing, the trees ran solid until freeze up, I witnessed the sap backing up into the laterals, then the drops, and eventually running right out around the spout. The trees were warmer and wanted to keep running. So, the question is, isn't the use of a new checkvalve or tap already compromised and the whole contaminated? I have had this happen in all of my woods before and it is not because it does not have enough slope. You could have 10% slope and with the trees running as hard as they do sometimes, then you get a very sudden freeze up, the sap will not ever be able to drain fast enough.