Preserving Herbs

 Most of us who grow herbs in our hydroponics eventually reach a point that we face the same question: What do I do with all these herbs?  I tend to pick what to cook based on what herbs I have to hand, but even still, eventually I can't keep up with how much are growing.  

For very short term storage, you can treat them just like cut flowers; place them in a cup or vase with water on the counter, or even in the fridge for slightly longer periods.  But that still isn't a long term solution. 

So, what to do with all the extra?

Before you start, always remove any blemished areas from your herbs, and the majority of the stems (small bits of stems connecting leaves are fine, but you don't want a bunch of sticks in your food.)

There are a multitude of choices, but these are the most common.

Drying

Perhaps the easiest method of preserving excess herbs to flavor your food at a future date, is to dry them.  It's also the most familiar - you end up with much the same thing as you would buy in the grocery store, except fresher - and thus with more and better flavor - and the satisfaction of having produced it yourself.  The quality (amount of flavor) will degrade over time, but you can always just use a bit more to make up for it.

There are two main ways to go about this (and a third way that is potentially less than a good idea).

Simplest of all, is air drying.  Many people simply harvest their herbs, and leave them sitting on the light hood to dry.  This works perfectly well!  It does have two potential drawbacks, though.  Firstly, because of the time it takes, more of the volatile oils that give the herbs their flavor can escape, meaning you get a bit less flavor left by the time it is done drying.  And secondly, should you encounter an issue - such as a bug infestation - you may lose the herbs you are drying in addition to your plants.  

You can also purchase mesh racks on which to dry your herbs.  This eliminates the second potential issue, assuming you dry them away from your gardens, but not the first.

The other method, which is the one I generally opt for, is drying with heat, either in a dehydrator, an oven, or an air fryer.  

For a dehydrator or air fryer, your machine should have instructions on how to go about it - there are too many variables for me to list them all here.  

For oven drying, my method of choice, simply lay your herbs out in a single layer on parchment paper in a cookie sheet.  For large herbs, like long fronds of dill, you may have better results chopping roughly, but don't get carried away - you just want them to fit on the cookie sheet well, you aren't trying to get 'seasoning size' pieces; that will come after they are dry.  Chopping finely before drying will let too many of those volatile oils escape, which, again, is where your flavor comes from.
Place your sheet of herbs in your oven, and turn it on to the lowest possible setting (even to just 'keep warm' if your oven has such a setting.)  Check hourly (or every half hour when they get close).  They are done when all parts of your herbs are crispy - if they have any give to them, there is still too much moisture and they have the potential to mold once you store them.  Take them out and allow them to cool a bit, then crumble them into seasoning size, and store in an airtight container.  I highly recommend these jars, whose amber coloring keeps out UV and helps preserve their freshness even longer.

The third, and possibly problematic, method of drying is microwave drying.  Although it sounds like an easy shortcut, it is actually more intensive and comes with risks, as well.  

If you choose to try this method, use a microwave safe plate, lay down a paper towel, and arrange your herbs on top of it, and cover with a second paper towel.  It will take somewhere from 1-5 minutes to dry the herbs, but you should check on them every 20 seconds or so after the first minute.  In addition, you need to watch them the entire time, because there is a small but real risk that either the herbs or paper towels can catch fire; thus, this method is not recommended by microwave manufacturers.  This risk is reduced by not drying the herbs entirely, and allowing them to finish by air drying - at which point, you have only reduced the time required from just letting them air dry in the first place.

Freezing

The next simplest method of preserving your herbs, is to freeze them.  This method has a few more drawbacks than drying.  The main one is that the quality of your herbs can decrease a lot faster (and more dramatically) than dried herbs; however, for the weeks or months that the quality maintains, the flavor is much closer to fresh than dried.  Once that period is over, however, you begin to not only get less flavor, but can get 'off' flavors, such as so-called 'freezer burn'.  Also, some herbs will turn an unattractive black or brown color when frozen, but this generally doesn't affect their flavor.

Although you can certainly just stick your herbs in a zipper bag and put them in the freezer, there is a simple way to maximize longevity and ease of use.

Lay out a line of paper towel (it can be useful to leave the roll attached to make sure you have the right amount of length.)  Arrange your herbs in a single layer on the paper towels - they can be close together, but you don't want them to overlap.  Leave a bit of empty space at one end of the paper.  Once they are all situated, fold the empty section over the first section of herbs, then carefully roll up the paper towels, jelly-roll style, and place into your freezer zipper bag, gently squeeze out most of the air, and place in the freezer.  When you're ready to use the herbs, just unroll enough of the paper towel to get the amount you need.  

Flavor Cubes

This is a slightly more complex method of preservation, but it does a very good job for long term storage, and frankly, it's just rather fun.

Gather your fresh herbs, and chop them up finely.  Pack them firmly into ice cube trays - I highly recommend silicone ice cubes trays for ease of removal.  These mini cube trays with lids hold right at 1 Tbsp, which makes portioning easy, and are what I use.  Then fill the remaining space with a liquid; you can use water, broth, or olive oil, depending on preference and how you intend to use them (or make some of each!)  Allow them to freeze fully, then put them in freezer zipper bags with as much air removed as possible for storage.

You can also store basic pestos (blended herbs, oil, garlic, and usually nuts and/or cheese) this way, which makes it super easy to add to recipes.  

Other Assorted Methods

In addition to the main methods of herb preservation, there are other ways to use your herbs that extend their useful life, but mostly are either very narrow in terms of use or storage time.

Herb butters are a fun and tasty way to make use of your herbs; simply partially melt butter (20-30 seconds in the microwave is usually just about perfect for me) and mix in your chopped herbs, along with any other seasonings you want (salt, pepper, garlic, etc.)  Store in the refrigerator for up to 2 months if well sealed, or in the freezer up to 6 months.

Oil infusions are often touted as a method of incorporating herbal flavor in your cooking, but it does carry a small risk of growing botulinum bacteria, which cause botulism.  Thus they should be stored in the refrigerator and used within 2 weeks.
Vinegar infusions, on the other hand, have a low enough pH that botulism is not a concern.  This can be a great alternative to include herbal flavor in salad dressings - just mix the herbal vinegar with an equal amount of oil and other ingredients as desired.  Place your herbs in the vinegar, making sure there is enough to fully cover the herbs, and allow them to soak in it in a dark, cool location for anywhere from a week to a month.  Gently shaking once or twice a day will make sure none of the herbs are exposed to air, where mold or other undesirable microorganisms can grow.  Once the herbal flavor is sufficiently infused into the vinegar, remove the herbs by straining through cheesecloth.  The resulting flavored vinegar can last indefinitely.

Herbed salt is another method, which can give you years of use and preserves the flavor particularly well - but of course, it isn't suitable for those on low-salt diets, and the amount of herbal flavor you get is directly tied to how much salt you use, which can be less than ideal.  To make herbal salts, start with about ½ c kosher salt or coarse sea salt for each cup of fresh herbs.  Using a food processor of knife, roughly chop the herbs with a tablespoon or two of the salt.  You want it to end up looking rather like sand, or like the salt did to begin with; you don't want a paste or fine powder.  Spread this out on a cookie sheet (parchment paper optional but recommended), and sprinkle the remaining salt on top.  Allow it to air dry for a few days, or bake on your oven's lowest setting for 1-3 hours (depending on how thick your herb/salt layer is).  Then store in air tight container, like a mason jar.  You can skip the drying, but then it needs to be stored in the refrigerator and used within a month or so; fully dried, it can last in a sealed container almost indefinitely, though like regular dried herbs, can gradually lose flavor after a year or so.  Sugar can also be used in much the same way with appropriate herbs (such as mint, lavender, lemon zest, etc.)

(Image courtesy of Marco Verch)