Vacuum-sealing extends the shelf life of herbs by preventing oxidation, but it doesn't prevent the decay and breakdown caused by surface bacteria and extreme temperature. Vacuum sealing works best with oil-packed herbs and dried herbs.
If you want to store fresh herbs without oil or drying, keep them on the stems and set them in a container with about 1 inch of water; then put the cover on the container or seal plastic over it with a rubber band. Store in the refrigerator.
You can keep dried herbs in a vacuum-sealed bag indefinitely, but they start to lose their flavor after six months. You can store vacuum-sealed oil-packed herbs in the freezer indefinitely without a loss in quality.
Wash the herbs as soon as you get them home. About 1 minute of thorough rinsing under cold water followed by patting dry with paper towels and air-drying eliminates the majority of surface bacteria that cause decay. In other words, rinsed herbs stay fresh longer than unrinsed herbs. You can also dry off the herbs in a salad spinner.
Cut a piece of plastic-bag material -- included with the vacuum sealer -- large enough to hold the herbs plus an extra 3 inches. Seal one open end of the plastic with the vacuum sealer.
Add the herbs to the plastic bag in a flat, even layer. If you're freezing oil-packed herbs, add the herbs and just enough neutral-flavored oil to coat them.
Flatten the bag as best you can, still allowing 3 inches of space at the top. Be careful not to let any oil squeeze past the 3-inch buffer at the top of the bag, as it can interfere with sealing.
Seal the open end of the bag using the vacuum sealer. If you're sealing multiple bags, allow the vacuum sealer to cool for 20 seconds between use.
Grind dry herbs to a fine powder for a concentrated flavor that works well in a spice rub or paste.