"...gold coin grass tincture which requires an alcohol content of 20-28%."
-depending upon the instructions you're following, almost always, the final alcohol content is much lower than what you're actually supposed to start with (if that makes any sense). Most all tincture recipes that I've ever heard of (and I've made quite a few) start with a minimum of 100 proof (which is 50% alcohol 50% water) for steeping the herbs.
That's because it's the alcohol (not the water) that is responsible for extracting whatever "goodies" out of the herb. The higher the alcohol content with which you start, the higher concentration of "goodies" you end up having. You can always dilute the tincture after you've extracted the goodies...but the more water one uses in the extraction process, the less potent & effective the tincture will be.
And if I have the time, I usually double or triple tincture whatever it is I'm making . Double tincturing = once you've completed the tincturing process and have strained all the original herb from the 100 proof alcohol solution, then you start the process completely again with fresh herbs, this time using the already tinctured solution as the starter alcohol...talk about effective - wowzah!
Like I said, I don't know what recipe or instructions you're following, but I wanted to add this information for your consideration.
Congratulations on making your own - no matter how you do it, it WILL end up being more effective than virtually anything you can buy, anywhere!