Don't boil it down to goop, that would be extremely frustrating to work with. Boil a known amount down to dry crust. Once your pot of mimosa extract has boiled down to a low volume, transfer it into a non-stick frying pan. The more it boils down the lower you want the heat to be to avoid burning the extract. Heat should be extremely low when it starts to get syrupy. Eventually you'll have dry brown crust. I put the cooled pan in a paper grocery bag to catch the flakes that fly off while I scape the pan clean with a plastic spatula. Dump the flakes from the paper bag into a zip lock bag and squeeze it to break the flakes into fine powder. It should look like instant coffee. Then encapsulate.
The onset using this method takes FAR longer -- up to 2 hrs for me versus 25 minutes drinking tea. I need more mimosa, but it also lasts much longer (3 or 4 hrs vs. 1 hr for me with the tea) and I rarely get nauseated using this method (most likely because of the more gradual onset). If you want to get a quick boost just empty the capsules into hot water and stir and you get instant ayahuasca tea. I've used this method dozens of times successfully. I usually use 12 - 14 grams for about the same intensity as 10 or 11 grams of tea. The amount of powder will vary based on how well you filtered the mimosa matter out of your solution. I've had doses vary from 9 double zero capsules to 20. I have no idea why this method isn't used more. It's a no brainer and you can prepare large quantities this way that don't have to be frozen to store. Just be sure you know how many grams the powder in the bag came from, and use the weight of the powder to dose proportionally. It's possible to make the onset faster by using a syringe to inject the capsules with a little water before swallowing them.
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