Dry ice extraction is the process by which the crystals (called trichomes) that grow on herbs are separated from the herb in the most efficient manner. This is desirable in the case of cannabis for instance, because the crystals hold the highest concentration of THC. The dry ice extraction method is by far the fastest, cleanest, and most effective method available today.
The previous method of crystal extraction was done with a large five-gallon (among other sizes) bucket, multiple bubble bags and ice water. But that's not all, you also need a mixer of some kind, one that attaches to a drill is best, and an old-fashioned ice scraper.
After set-up, you mix the ice, water and herb mixture for 20-40 minutes. After straining the bubble bags, you scrape the product left on the screens with the ice scraper and that is your extract.
Compare that with a dry ice extractor. A dry ice extractor has one container and one bag with a 185-micron screen. That's it. No need for water, a mixer or an ice scraper.
By combining the herb and dry ice in a can and poly bag, then vigorously shaking them, the result is the desired extract within second…not hours. A video shows the process here. (http://www.kangacan.com/catalog/dry-ice-extraction-videos.html)
Dry ice is the perfect material for the process for a couple of reasons. First, it's five times colder than regular ice. This removes the crystals faster and more efficiently. Dry ice doesn't melt, it sublimates. An incorrect layman's term would be "evaporates." The process of sublimation takes the dry ice from its solid form to its gaseous form. This results in a far cleaner extraction method. The dry ice because of its extreme cold temperature makes the trichome stock brittle which causes the crystals to harden and fall easily from the plant.
After just 40 second of shaking the herb and dry ice, the extract will fall through the screen (and onto a clean surface.) This first batch of the extract will have the highest concentration of THC. Continue for another or so, and you will have more extract. This will a slightly lower concentration of THC, but will still be of excellent quality. Continue this process for three to four turns.
You will see the color of the extract change from a yellow gold (highest quality) to a brownish green (lowest quality.) And that brings us to the final advantage of the dry ice extraction method. No need for multiple screens. The additional shaking does the job that five bags with different sized screens used to do. You just need one bag and one screen.
That's it, the entire process can be completed in less than ten minutes.