Any tips, tricks or must have devices for getting a moisture content on “dried” biomass?
The last batch the boss dragged home looked to be 20% water by the only method I could come up with on the spur of the moment.
I put a 507g in my vac oven at 70C overnight, and came back to less than 400g (394g) the next day.
I think 2% terpenes is being generous here, which leaves me at 20% water.
farmer (and boss) swears they tested it at 10%
I’ve got five new samples in the oven right now, and I expect similar results when I get into lab.
I can’t imagine the the moisture meters folks use for testing firewood etc are up for the task, given the non-contiguous nature of hemp in a super-sack, so what is the right tool for rejecting wet biomass before it gets in the door?
eg: this strikes me as bogus…
Edit: I also left that nice dry 394g out in our non-climate controlled warehouse, to demonstrate (to you know who) that just because stuff comes in the door dry, doesn’t mean a damn thing if it’s stored at ambient conditions in the PNW rain forest. it had gained 12g by the end of the day, and has probably gained more over-night.
Can be a bit pricey but have you considered a water activity meter? It’s a more absolute value than moisture content % by weight. Not super portable but I’m sure you could make it work.
Primarily because “% moisture” seemed easier for the others involved in the transaction to wrap their head around.
given the variety of options out there, I’d still appreciate a leg up (product review ) from anyone using a portable (or lab based) water activity meter to screen their incoming or out going biomass.
the pawkit (is that Australian for pocket?) seems portable enough.
Aw down to .003 in 5 minutes. Good for lab/intake. Partner with a core sample of each bag. Aw below a certain point will prevent mold growth. Not sure how far below that you need to get to 10% moisture, but at least the biomass won’t spoil.
I have a bunch of waterproof humidity sensors that could probably work to get a decent idea of the moisture content of the middle of a hemp bale.
I bought them when I thought I could use them for soil moisture sensors…but they are humidity / temperature sensors so pretty much always read 100% humidity until the soil is too dry. I don’t know why they are marketed as soil moisture sensors.
When testing for moisture content, those wood meters won’t do a good job. Like you said, you need to dry the sample out for real, in an oven, low and slow, ideally convection. To find the % of weight loss for % moisture content (some of which is volatiles like terps, but they will be minor compared to water weight)
P.S. The other white papers by the Cannabis Safety Institute are equally gold. The pesticides on is great.
EDIT:
Sampling and homogenization of sample is important for an accurate representation of the whole mass.
We recommend that 5g per pound be sampled from every batch of Cannabis, in 5 individual, randomly chosen one-gram increments. All of these sub-samples should be combined together for the entire batch (for instance, a 5lb batch would require 25g of total sample material).
The combined sample must be thoroughly homogenized, and the appropriate volume removed for the performance of each assay.
Statistical sampling procedures are detailed in the protocols found in ISO 7002:1986 and ISO 4874:2000, and all laboratories should have published Standard Operating Procedures modeled after these. We further recommend that batch sizes be constrained to 5 or 6 pounds. Smaller batch sizes lead to testing prices that are overly burdensome to producers, whereas larger batch sizes lower the detection thresholds of certain assays.
Moisture content isn’t an accurate way to find the Aw of a material.
Water Activity is a Ratio of Vapor Pressures
Water activity is the ratio of the vapor pressure of water in a material (p) to the vapor pressure of pure water (po) at the same temperature. Relative humidity of air is the ratio of the vapor pressure of air to its saturation vapor pressure. When vapor and temperature equilibrium are obtained, the water activity of the sample is equal to the relative humidity of air surrounding the sample in a sealed measurement chamber. Multiplication of water activity by 100 gives the equilibrium relative humidity (ERH) in percent.
aw =p/po =ERH(%)/100
As described by the above equation, water activity is a ratio of vapor pressures and thus has no units. It ranges from 0.0aw (bone dry) to 1.0aw (pure water).
I agree completely. Directly testing Aw is the way to go. I only wrote about the measured relation of Aw to cannabis flower moisture content to help other people in this thread.
I recently spoke with a salesperson who recommended using a Tuneable Diode Laser to measure Water Activity in fresh cannabis, Rich-Terpene extract, and vape carts because other sensors get contaminated by terpene vapors condensing in the aqueous or capacitance sensor cells. If that’s the case, we could be looking at a $13,500 instrument in order to avoid accumulating an offset with this measurement. Any thoughts?
Bump. Anyone happy with what they are using for testing water activity? Going to be getting something for use in the lab soon and still am not set on any particular machine.
The equipment suitable for the measurement of water activity can be the same as that used for the measurement of relative humidity provided that the sensing element used can be made captive or otherwise isolated with a sample of the product to be measured. A basic measuring technique utilizes a sealed dish or container with the sensor mounted above the test sample.
) from anyone using a portable (or lab based) water activity meter to screen their incoming or out going biomass.
