I began the process of making a batch of comfrey tincture three days ago. I am posting the steps in case anyone wants to make some too. I have developed, by trial and error, what I believe is the best method.
Part one is a process called decoction which is a low temperature slow cooking process. Decoction is used because we are trying to get useful product out of small pieces of fibrous roots. Using a low extraction temperature requires a long period, but the active ingredient Allantoin is stronger if lower temperatures are used.
The ideal set point seems to be 145 degrees F, but must always be over 140, or the batch will spoil. If a batch spoils, it must be discarded, and you must start over. It is better to loose a small percentage of the strength than to loose a batch! So if you can't hold it very tight, run it at 180 degrees, and save the batch.
Here is a 5 quart crock pot I use for decoction along with a simple non contact thermometer.
Use distilled water to avoid introducing unknown chemicals into your decoction. Not trying to insult anyone by being basic, but keep the lid on, stir the decoction, and add water as needed. If you do not, the outside will stick, and get unfair attention from the heating elements. This will weaken the Allantion in the final batch, and can add a burned smell. Neither is fatal, but neither is good either. This will cook from a week to two weeks, depending on the size of the particles of dried root used.
So, how do you know when it is done? Comfrey helps, because the muscillage in the comfrey is the last thing to be released. When it thickens, and you will notice the difference when you are stirring it, the decoction is done. It will thicken and act kind of like syrup, mixed with kitty litter. You have a successful decoction and you are done with Part one!
Part two will be the extraction process, which I will show you, as soon as I have a good decoction!