It’s “all about alchemy and personal preference,” says jerryc123. You don’t have to rely on commercial suppliers; you can infuse liquor with spices such as lemongrass, kaffir lime leaf, citrus peel, and wild cherry bark, adjusting as you please. Infusions of sassafras and sarsaparilla are particularly delicious, says mrgrotto (they work well in Old Monk Rum). mrgrotto infuses each ingredient as a separate tincture, and then mixes from there.
One problem with homemade bitters is cloudiness and sediment. To cure this, ShadowedOne recommends filtering the bitters first through a coffee filter. “This process takes a long time, but works well to get out the large sediment,” he says. “Following that I allow the bitters to settle for about a week then siphon the clear bitters off the top being careful not to disturb the sediment.”
And don’t be afraid of 151-proof rum when making bitters, advises jerryc123. “Keep in mind, the higher the proof, the more flavor will be extracted from the base ingredients,” he says.
Board Link: Homemade Bitters