Metabolism

[doocat]

We had some metabolism last season in the earlier light syrup. I am curious if anyone can tell me if this is a fluke or if it will return year after year now? Maybe Dr. Tim....

Thanks

[DrTimPerkins]

I am curious if anyone can tell me if this is a fluke or if it will return year after year now?

Ask me again next May. :D

There seems to be a tendency for some sites to develop metabolism off-flavor more than others, but if this is the first time you've noticed it, then it was probably just a fluke. Did you perchance do a lot of retubing or change a lot of drops before this past season? Sometimes if the tubing is new or super-clean, the syrup produced is such high quality (light in color/flavor) that any amount of off-flavor is more noticeable. Often it'll disappear part-way through the season as things gunk (sorry for the technical term) up a bit.

[GeneralStark]

I attended a seminar at a VT Maple School several years ago and the presenter who is a researcher at Acer suggested that high vacuum may be a factor early season with metabolism. He did not explain why or how, but I thought this was quite interesting.

[DrTimPerkins]

...suggested that high vacuum may be a factor early season with metabolism.

I have also heard that said (second-hand). To my knowledge, that finding was never been published, so I don't know whether it was the result of a research project or was pure speculation.

[doocat]

We did replace about 2000 of our drop last year! Never really noticed it be for or at least not like we had it this last year. We made a lot of light syrup as well probably half of our crop or better.

Thanks

[DuncanFTGC/SS]

OK, I will bite, what is metabolism as it applies to maple making?

[DrTimPerkins]

OK, I will bite, what is metabolism as it applies to maple making?

"Metabolism" is an off-flavor in maple syrup that often appears early in the season in light syrup, but typically goes away after a few good sap runs. It is very difficult to blend out due to the low threshold for odor/flavor (a little goes a long way). Some people refer to it as "woody". To me it tastes very heavily musty, but others describe it as popcorn tasting. In any case, it is very nasty tasting stuff. It is also distinctly different from "buddy" off-flavor, which more often affects dark syrup at the end of the season.

Metabolism is caused by pyrazine compounds derived from naturally-occuring amino acids in the sap. Very cold winters with little opportunity for recharge and high soil nitrogen conditions are associated with metabolism. Some sites seem to be more prone to experiencing this problem, and in some years a significant portion of the crop can be affected regionally. There is more on the UVM PMRC website at http://www.uvm.edu/~pmrc if you're interested.

[DuncanFTGC/SS]

Thank you Dr. Tim, the more you know! From reading the first couple posts, I was thinking that it had something to do with unclean tubing. Now I understand that anyone can end up with this. If you get it, do you start tasting your sap, or just keep boiling till it goes away?

[DrTimPerkins]

If you get it, do you start tasting your sap, or just keep boiling till it goes away?

Unfortunately you cannot taste it in your sap. It is only when it gets close to syrup that you can smell or taste it. Often people won't even notice it then, but only find it when they open a barrel to pack syrup later on when they fund it. If it does occur, the only way to deal with it is to boil to a very high density and redilute back to syrup density, and repeat until the metabolism is volatilized off, and more good flavor is developed. This is far easier to do NOT in the evaporator, but in a flat pan (finishing pan) where you can control things a bit better. The result is that the off-flavor is reduced, and the good flavor is heightened, but the end product will likely never be terrific, just far better and more easily diluted out. This problem and the remediation process is described in the publications on metabolism at http://www.uvm.edu/~pmrc/?Page=publications.html

[GeneralStark]

My understanding is that turning the syrup into sugar will essentially remove the off flavor as the compound volatizes when boiled to a high temp. as described.