Drake's sources keep each herb in its own jar. You combine the herbs in small batches as you use them (Student's Manual, Basic Course, p. 25). Extracts are stored by herb type and combined by ratio before use (Cho's Solutions, p. 9).
The ratio is 2 angelica to 1 licorice, 1 cinnamon, 1 garlic and 1 ginger (Cho's Solutions, p. 9).
One farmer asked about premixed OHN that sat for two months. Drake said to keep using it, as long as it wasn't pre-diluted with water (Office Hours Ep. 41, 1:05:42).
The library does not say whether an angelica and cinnamon mix is ruined, or how it affects shelf life or strength.
