I would not use them. If you want to make concentrates which last a year or so than you should look at fermented stuff such as FPJ (fermented plant exctract) and similar.
Recipes can be found here – http://theunconventionalfarmer.com/
Instructions for fermented plant extract:
Find a fast-growing plant in your area. It must be a green-color plant, fresh juicy succulent leaves are best.
Collect a bunch of the growing tips of the plant. The green leaves give you Nitrogen, the growing tips give you the growth hormones. We try not to wash them for you may wash off those microbes too. We want the photosynthetic bacteria that naturally occur on the leaf surface of these fast-growing plants (phyllosphere microbes).
Weigh the amount of material you’ve collected and add roughly half that weight in sugar.
Put in a clay jar or plastic container.
If fermenting a large batch, put a large rock on top of the material to push it down into the bottom of the container. After at least 5 hours, remove the rock, and cover the container with a newspaper/cheese cloth/etc and secure with string/rubber-band.
If fermenting a smaller batch, you can add water. Add at least enough water to cover the material but if you want to add more no problem.
Keep container out of direct sunlight. Solution will be fermented in approximately 7-15 days (depending on temperature).
After that time, drain the liquid and put in plastic bottle, leaving 1/3 empty so organisms can breathe.
DON’T TIGHTEN lid for at least 2 weeks or so. Wait till tiny bubble disappear and then close the container tightly.
Note: if you observe un-dissolved sugar in the bottom it means fermentation did not go to completion. Add a little water to reactivate and leave lid off for a few days.