the trick to getting higher infusion potencies is to do a counter current extraction — divide your total 1.5 lb batch of ground biomass up into several smaller batches, say 10 minibatches of 70 grams each. Put one minibatch in a french press and fill with carrier oil until you have covered the biomass and let it steep for 10 minutes or so - mild heat, say 40degC, can help too. Record how much oil you added because this will be your ‘wash’ volume. After steeping the first wash, strain the oil you can with the french press into ‘tank 1’—this tank will be your most potent infusion. Then refill the french press with another wash volume of fresh infusion oil. Steep then strain into ‘tank 2’ — this will be your be your ‘medium potency’ infusion. Do a third wash by refilling french press with the fresh carrier oil, steep, and strain into a low potency infusion, tank 3.
Continuing this method will step up the potency in tank1 the fastest. I haven’t collected rigorous data in a while but with this french press method I made 24 mg cbd/g oil in my first tank after three minibatches. With your 18% biomass you will probably make quicker progress.
Of course you will notice that after straining the first wash of a minibatch you won’t get the same volume of oil back that you put into it. So after three washes tank one will have less oil than tanks two and three. So for your second minibatch and afterwards, your first ‘wash’ should comprise all of tank one and a little bit of tank two to get the biomass coverage you need. Similarly, the second wash will take what’s left of tank two and some of tank three. Finally for the third wash you can make up to oil that gets stuck to the biomass by adding fresh infusion oil to what’s left in tank 3.
The beauty if this method is that it pulls cannabinoids very effectively while leaving weak potency oil stuck to the biomass after your third wash. Btw you can of course do more than three washes to more efficiently extract the biomass but three tends to get 90% or so.
Eventually the tank 1 potency will exceed your spec and you can take it out of the process. So your first wash of your next minibatch starts with tank 2, then tank 3, followed by a full wash column of fresh carrier oil. For 18% biomass, 10x70 gram minibatches, and a target potency of 30 mg/mL, my guess is you would take some infusion out after every second minibatch.
When all minibatches are run—you are left with the tank 2 and 3 infusions that are ‘low potency.’ For this reason you really need to divide your overall batch into several minibatches to ensure that as much of the cannabinoids end up in the high potency oil as possible. The tradeoff on minibatch size being: more minibatches equals more work.
So yeah I think you could do this with a french press and a few beakers. For decarb, I would find a vessel that fits in your oven and do it there, at low temp (100 degC) to let co2 release and maybe some water will boil off too. Then filter and voila! Some people don’t like the taste of infusions like this—some can carry a bitter ‘bite’—but others taste quite pleasant and resemble the starting biomass really well. Since you are going to capsules taste is less an issue anyway.
Before you run a 1.5 lb batch, try a really small run with a syringe & cotton to see if it’s up your alley.