Refractometer technique and readings?
I just got my new toy in the mail, and I squished up a three inch fan blade and got a clear reading of ... 17. This plant should NOT be reading 17. It's from my 4 week old Super Lemon Haze in mineralized Pro-Mix with no cooking time, other than the 2 weeks it's been in the pot - no foliars, no drenches, no nutes, no nuttin'. It just showed its first flowers two days ago. It does look like a high brix plant, though, with very shiny leaves and strong vigor, which is why I selected it to read.
What are the possible explanations? For instance, I didn't want to waste enough leaves to get 2 entire "drops", so I only managed to smear "juice" on the glass, from one 3 inch fan blade. I made 2 earlier attempts with less leaf and got no reading at all - had to get enough to smear fluid across the glass, and then got the 17, clear as a bell. If there had been more fluid, would the reading have been diluted and shown fewer dissolved solids, and a more reasonable reading?
How tricky is the method of extraction?
Great question!
With any technique, be it picking a guitar or making a complicated sauce in the kitchen, results vary depending on the individual. This normal variation is due to technique....as is the variations we might see with testing a sample.
We're trying to test the
INTRAcellular juices, as in the juice that is inside the cell wall. This dictates crushing the cell wall of millions of cells.
A stainless steel mortar and pestle will work. Throw a handful of leaves in there and mash them up for say 30 seconds. Gather the pulp in a piece of cheese cloth and squeeze 3 large drops or more of juice onto the prism. Grind the sample for the same time duration and with the same grinding technique and cadence each every time you take a reading and you can mitigate
intraoperator error.
Intraoperator error means you make enough mistakes to where your readings vary one from another due to random, sloppy technique.
If you use the same make and model of refractometer, test your samples at the same time of day each and every time, and use the same technique as someone else, this can increase interoperator consistency. IE, you and I sample the same way, so our brix readings are somewhat equivalent.
Here's my method:
I take sample in the dark, often right before I foliar feed....never after. I do this because I take brix readings when I trim and prune.
Here's the important stuff:
Get a tool that will pulverize the cell wall and get real juice that drips from the leaves. Make sure that tool is clean.
Calibrate the refractometer in the room you'll be doing the pruning, crushing, testing in AFTER it has assumed room temperature. Store the tool in the room....no problem.
I take leave, petiole and sometimes young flower samples. Work 4 or 5 leaves with petioles into a ball, and place them in the "crusher," which yields a few drops of whitish green, frothy juice, which I drip onto the prism....plop, plop.
Snap the lid shut and take a reading. I get a clear, concise line on my meter.
In veg, a reading of 12 is fantastic! 10 is fine. Brix levels don't really rise until the plant starts to respirate during bloom. Anything over 12 is great! 14 or 15 is superb! Some strains can go even higher....my highest was 18, but I did have some plants steady at 17 for a while.
It's good to ritualize your reading practice. Take them at the same time, the same way, each and every time. That way, in YOUR garden you'll know if 17 means no bugs....shoot for 17 or higher. In the same way, your technique might give consistently lower readings....but consistent. You might find that brix of 10 keeps the bugs and mold away, and that you can't seem to get them over 12, no matter how hard you try.
It all comes down to technique and the accuracy of the instrument.
I had years in the lab, nearly blowing stuff up and doing some pretty cool things. This was back in the days when bunsen burners were gas fired and benzene was used all the time as a solvent....so I have lots of hands on training in lab equipment and sampling techniques in general.
Keep everything clean. Make sure you can pulverize the sample. Squeeze juice, not pulp, out of the sample using cheese cloth or a piece of screen.....do everything the same way each and every time.
Following the above, at the very least, you'll get accurate, consistent measurement for YOUR garden using YOUR tools and technique, and with that data you'll be able to improve your growing skills.
Poor technique can result in artificially high or low readings.
