TOKABIGONE asks a good question:
" Can I add the used bud after dry ice sift to the other oz for tincture with alcohol? I would think there would still be cannabinoids left that could be extracted with the alcohol, right or no?"
That's a good question and the answer is that there is certainly some THC left after sieving, but the amount isn't clear. Is it worth putting the residue through a QWET extraction? I took an empirical look at that with the following results. (note, I'm using "THC" here to mean all cannaboids including CBD, CBN etc.)
The issue boils down to whether you should use your precious EverClear 190 alcohol to extract the residual from depleted weed. I am lucky to have an easy & fairly inexpensive source of 190 ethanol (EverClear) here in MA. Elsewhere it can be very expensive or unavailable. So, I don't bother attempting to reclaim the alcohol from my tincture, I just evaporate it away down to the concentration I want. Since I grew the weed for my consumption, one way or the other, my cost for a batch is few oz of EverClear.
The QWET extraction is pretty effective, about 75% of the THC in the bud is transferred to the alcohol. So a typical batch for me is about ten grams of herb and six ounces of EverClear. If the weed has 20% THC and I can extract 75% of that from my 10 grams (=10,000 miligrams), then I'll end up with about 1500 miligrams of THC. Here's the math:
10,000mg x .20(%) x .75(%) = 1500mg of extracted THC dissolved in my six ounces of EverClear. A typical dose might be 15mg of THC, so you've just made 100 "normal" doses of tincture. Cost is 10grams of my stash and about $5.00 worth of EverClear for 100 doses.
If you do the same calc on depleted weed with say 75% already extracted using dry ice, so your herb is down to 5% THC instead of 20%. Our same 10,000mg of depleted weed now only has 500mg left to give and QWET can only extract 75% of that, so we end up with 375mg, about 25 normal doses. Your cost is still about $5.00 worth of EverClear, for about 25 doses. Adding the depleted weed to fresh doesn't help because you'll need more alcohol to extract from the increased weed. 6 oz alcohol for 10 grams, 12 oz for 20 grams, etc.
In all fairness, many tincture aficionados reclaim the alcohol used in extraction, so, why not try to get the last trichomes?
That said, I doubt I'll ever try to salvage anything out of the soggy mess resulting from my bubble bag adventures , but that's just me.
I hope this is helpful and welcome any corrections or suggestions from more experienced Tinturados.
-Grouchy