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I would like to grow mushrooms on oak trees I can harvest from my property. I've read that the best results will be when the sap is rising but the tree hasn't budded yet. The mycelium feeds on the sugars in the logs.

I would love to be able to measure the sugar content so I could accurately asses the sugar content. Here in Southern Oregon the winters are mild and the leafing out of the oaks varies quite a bit from year to year.

How can I measure sugar content of the sap in a tree?

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Interesting, +1. If you don't get any answers here after a few days, try Chemistry.SE. –  terdon Jun 5 '13 at 2:05
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The soluble carbohydrate can get the mushrooms off to a good start, but it is the cellulose that will be most important for production. Another reason people innoculate logs in winter is because there are fewer spores from competitors in the air, and less work to be done in the field (for farmers). –  Abe Jun 6 '13 at 22:08
    
Yes, @Abe, an excellent point. Also many fungi can degrade lignin so this would also be a carbon source. –  Alan Boyd Jun 7 '13 at 11:57
    
@alan even if lignin degraders breakdown lignin and can utilize some of the products, I don't think the lignin itself results in a net benefit to the fungus (because ligninases are so costly to build) it is the cellulose inside the lignin matrix that they are after. –  Abe Jun 9 '13 at 18:04
    
@Abe - I didn't know that - any references? –  Alan Boyd Jun 10 '13 at 6:43
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1 Answer

up vote 2 down vote accepted

The difficult step will be getting samples of sap: have a look at the WP page for maple syrup for ideas about methods of tapping into the xylem of your trees.

You will then need to assay sucrose in the sample of sap. There are many commercial assay kits available (Google: sucrose assay), which rely on an enzyme, invertase, to convert the sucrose to glucose + fructose. The released glucose is then measured by a glucose oxidase assay. You would need some kind of colorimeter/spectrophotometer for quantitative results but there is a visible color change, so you could probably get a rough idea of what is going on by visual comparison with a set of glucose standards.

Supplementary
An alternative would be to measure sugar concentration by refractometry: see here and here.

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Is sucrose the most common disaccharide in sap? –  terdon Jun 5 '13 at 14:05
    
I can't say for certain. Here is a reference for pedunculate oak: onlinelibrary.wiley.com/doi/10.1055/s-2001-12898/abstract Sucrose is 2x more soluble than glucose or maltose, so may be the best choice for transport in aqueous solution. The assay would, of course, pick up glucose. –  Alan Boyd Jun 5 '13 at 14:18
    
Seems reasonable enough, thanks. –  terdon Jun 5 '13 at 14:25
    
Seems as if you can collect sap from cutting the end of a twig. tywkiwdbi.blogspot.com/2011/04/… I wonder if, for my purposes, I can just monitor the quantity of sap production? I'm guessing that when the tree is producing the most sap would be the time that the most sugar will be in the logs I harvest. –  monty0 Jun 5 '13 at 15:41
    
A spectrophotometer is a great idea! spectralworkbench.org/sets/show/207 shows spectrograms for various stages of reducing maple sap to syrup. I'm guessing that a season of collecting and analyzing samples would show me whether sugar concentration varies over the course of the sap run. –  monty0 Jun 5 '13 at 15:46
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