Contributed by: Doctor Dangerous
What is the "Dry Ice Cure" (Freeze drying )?
What is Dry Ice?
"Dry Ice" is frozen Carbon Dioxide. CO2 will change from its solid, frozen state to its gaseous state without passing through a liquid state - hence its name dry ice. This process of solid changing to gas is known as sublimation.
What is Sublimation?
Sublimation is a simple process which depends on the fact that the surface of a frozen solid is actually quite active at the molecular level. In the case of water ice, water molecules are constantly leaving and binding to the frozen surface. In a moist atmosphere, more water molecules bind to the surface than leave, and ice grows on the surface (e.g frost inside your freezer). In a dry atmosphere however, more water molecules leave the frozen surface than adhere, so the solid dries out.
The same process occurs with Dry Ice. As there is a fairly low CO2 content in air, the dry ice sublimes away completely, leaving no residue or liquid - hence its name.
What is Freeze Drying?
Freeze drying (scientific name: Lyophilization) depends upon the process of sublimation (explained below), and on the fact that like CO2, frozen water at low temperature will go through the process of sublimation under the right conditions.
Dry ice has a very low water content, as it is made up of almost pure CO2. In theory it IS pure, but even from a lab suppliers, it will have a small amount of impurities - these do not matter for our purposes. In effect the dry ice vapour has near zero relative humidity.
Now: (this is the important bit)
When material containing water is placed into this almost zero humidity environment, the water molecules are drawn out of the material and into the CO2, raising the relative humidity of the CO2 and lowering the water content of the material. If the CO2 around the material is steadily replenished then the process will continue until all moisture has been removed from the material. All this happens at low temperatures, below the freezing point of water, which means that the material is preserved in a totally fresh state.
How Do I Freeze Dry Grass?
Use a container (I use a Tupperware box) that is twice as big as the volume of grass you wish to dry. Make a few small holes in the lid, to allow the gas to escape.
Put equal volumes of bud and dry ice inside, loosely packed, with the dry ice underneath the bud. Put the lid on and make sure it is properly sealed so that the only way for gas to escape is through the holes in the lid. Put the box into a freezer, lid upwards. This is to keep the material as cold as possible, prolonging the sublimation process for as long as possible. The dry ice will begin to sublime pushing all air out of the box and surrounding your buds with bone dry co2. The totally dry atmosphere will begin drawing water molecules out of the plant material.
Check the tub after 24 hours and then every 24 hours until the dry ice has all gone. When the ice is all gone -the buds should be completely dry and smokeable. If you find that they are not quite dry then put some more dry ice into the box, place the lot back in the freezer and wait until they are done.
Can I use a fridge?
You could use a fridge instead of a freezer, but the dry ice would evaporate very quickly so you'd need a lot more of it to dry the buds, hence the expense would rise rapidly. Better would be to use a cool box - one of the plastic insulated boxes for food storage when camping. Again - make sure that there are holes so that the gas can escape.
Do I need to prepare the buds?
It's better to partially dry the buds so that they are nearly dry, then finish them off with dry ice. If you use fresh, wet grass then you can expect the process to take much longer and to use more dry ice, pushing the cost up. I find that using partially dry buds in a freezer the dry ice has gone after about 48 hrs.
What I do is give them a week of slow dry, then manicure, THEN freeze dry them.
What are the advantages?
The advantages of this method are increased potency and a 'fresher' taste.
As the material is preserved in a totally fresh state, the THC glands suffer as little degredation from heat, light and air as is possible. No other drying process preserves the resin glands is such a fresh state as can be achieved with freeze drying.
Why should I freeze dry?
Freeze drying is good if you plan to freeze your bud anyway. If you don't want to keep it in the freezer then there isn't a lot to be gained by using the technique, as the 'fresh' thc will rapidly degrade as usual once outside the freezer.
Where Can I get Dry Ice?
You can get dry ice from most lab suppliers (expensive) but many industrial ice houses or ice cream suppliers sell it for considerably less (preferred option)
Just try the yellow pages.
My Opinion Based on Experience
To be honest, In my experience the dry ice cure is a lot of trouble for little benefit, as the final taste isn't as good as you can get by slow drying and glass jar curing. Generally it's greener tasting and somewhat 'minty' due to the remaining chlorophyll. Strangely enough, some people like this minty taste and associate it with strength. (weird, I know - but they do.)
Does it really increase potency?
I have tried comparison by using a control sample, and freeze drying definitely seems to give you a slightly higher hit with a mintier taste than the jar cure, but the overall strength didn't seem hugely different. It's a connoisseur smoke, perhaps. In a blind test at a party with about thirty people involved it came out about evenly split as to which was the strongest, but that was a subjective test, and was only conducted in a very stoned manner! According to The Frank & Rosenthal Guide, anecdotal evidence suggests that freezing improves potency, which is why I got into the process in the first place. I'm not convinced either way, but it was a fun technique to play with for a while.