One of the things that makes these dishes so special is that they're largely seasonal. Yes, if you definitely need your basil fix there are a few things you can do, but basil and tomatoes just don't seem to fare well when cultivated out of season. Hothouse basil plants you may run into in the market during winter aren't large enough to season a family sized dish, except maybe a marinara sauce, and you probably already know that store purchased tomatoes taste like pale pretenders compared to their homegrown counterparts. There are some workarounds for storing basil you should know about, though. You can net great basil in December, but only if you act now.
Harvesting Basil and Storing it Over the Long Winter Months
Basil doesn't dry well. I'll repeat this because I don't want you to be disappointed: Dried basil loses most of its flavor -- and that's being generous. To preserve that bright burst of rich savor and zest, you will have to find another long term storage method. Basil is a prolific plant, and if you grow it, there's a good chance you have lots. Big bounty means a harvest to share and hopefully preserve for future use.
What You Need to Know about Harvesting Basil
The best time to ramp up for a basil harvest is when the plant has lots of leaves but few flowers (There's a technical term for this that escapes me at the moment and you probably don't need to be bothered with it anyway.)
This is how the whole flowering business generally works: Many plants and most herbs have limited energy stores. At the beginning of the season, they expend energy producing leaves. Where most herbs are concerned, that's where the flavor is. There are some exceptions, like chamomile and lavender, where you're really after the flowers, but we'll discuss those herbs individually.
When you have a bushy plant with lots of leaves and the tips are just starting to elongate, that's the best time to harvest. After flowers form, the plant switches from being a leaf producer to being a flower producer. Since it's the leaves you're after, waiting until the plant has flowered and set seed is counterproductive. Pinching back the flowers is a method of forestalling blooming and encouraging the plant to keep producing leaves. It may delay blooming for a week or two under the right conditions.
You can also harvest basil in batches: Wait till a plant is at least 10 inches high and then start harvesting a third of the plant every month or so. You should wait until at least as much as you've taken grows in again before taking a second and third harvest. You get young, flavorful basil, but there's more work involved than taking a single harvest from each plant. To fill your basil needs throughout summer, take partial harvests from a few plants to use fresh, and leave some alone for a big summer or early fall harvest.
Tips for Harvesting Basil
With basil, the leaves are flavor central, and you want to gather them together in the morning before the sunlight starts beating down on them (well before noon), but after the dew has evaporated. Place harvested leaves in a container that allows good air flow. You can use a paper bag or a woven basket. Avoid using a plastic bag or bucket. Without air flow, the leaves will wilt fast and can actually begin to cook. As you harvest, be sure to keep the snipped leaves out of direct sunlight, too.
After harvesting, rinse the leaves gently and pat them dry.
Here are some storage options:
Freezing leaves - One of the most common methods for basil storage is freezing. There are two easy ways to do this. You can store individual leaves in a big freezer bag for later use. They're best frozen on a cookie sheet or plastic tray. As the leaves freeze, throw them in the bag. The leaves will stay relatively loose and individualized, making it easy to pull them out a few at a time later.
Making basil ice cubes - The other method is to make a slurry of fresh chopped basil and water and freeze it in ice cube trays. This is an "instant" basil approach you can use to add basil goodness to soups, stews and pasta sauces throughout the winter. It's a nice option that's fast and simple to do. Once the slurry is frozen, you can transfer the cubes to freezer bags for convenient long-term storage (and free up your trays).
Making Basil Oil
Basil makes a tasty flavored oil, and you can create basil oil pretty easily too:
Basil oil infusions - Transferring flavor to oil using fresh ingredients is typically called an infusion, and this can be accomplished with or without heat. The best example of a hot infusion is a steaming cup of hot tea.
Cold vs. hot infusions - In the old days, herb enthusiasts used to cold infuse lots of herbs in oil by just letting the herbs dwell in the oil for a week or two. Some recipes called for leaving the oil in the sun, while others suggested placing the oil in a dark warm location. I've made garlic flavored oil like this and then just stored it in my cupboard.
There are some BIG problems with this method, though. Salmonella (Salmonella enterica) is one, and botulism (Clostridium botulinum) is the other. Both can be present in cold infusions that aren't refrigerated. Nowadays, I use warm infusions for edible preparations that don't use large proportions of highly acidic (vinegar) or alcoholic (liquor) ingredients. You can find more information about salmonella and botulism below.
For hot infusions, the idea is to speed up the flavor transfer between the herbs and the oil and also to eliminate as much water in the herbs as possible. The more watery an herb is, the more quickly the oil will spoil. For basil, which has a relatively high water content, I use this recipe:
Basil Oil Recipe
1 cup avocado oil
2/3 cup tightly packed, rough chopped basil leaves
I use avocado oil and not the standard olive oil mixture because I simmer the oil and basil leaves in a slow cooker or in a double boiler for about an hour. This process distributes the flavor and helps remove the excess moisture (the oil will last longer that way). The long cooking time works well with avocado oil because, unlike olive oil, it's super stable and has a very high smoke point. It's delicious, too.
Basil oil prepared this way has a complex basil flavor you'll like. After processing, I strain the mixture through a sieve and then through a coffee filter. It will last a month in the fridge. I typically break the batch into thirds and freeze two portions. This will usually get me through the winter months. The recipe can be doubled.
Another option is to prepare an entire dish containing basil and freeze that. I've had success freezing pesto, the same goes for any number of Italian sauce and pasta variations. If you have a few favorites that sound like good fall fare, take advantage of your basil harvest by preparing and freezing those recipes now.
When you're harvesting basil, don't forget to let a couple of plants, or portions of one plant, flower for seed. Basil is very easy to grow from seed in spring for a big, new batch of thoroughly delicious basil next year.
Harvesting Basil Seed
Most basil varieties have large black seeds that form on the flowering spikes. I have some harvesting photos and instructions here: Harvesting Basil Seeds.
Botulism - Botulism is present in soil. It needs an airless, low acid environment in which to develop from a dormant state. If you create herbal recipes using fresh ingredients and refrigerate them at or below 39 degrees F. right away, or use alcohol or vinegar as a base, the chances of botulism contamination are low. The problem with cold infusions left at room temperature using anything other than alcohol or vinegar is that botulism does have days to develop and later refrigeration or short term boiling won't destroy the toxin. For more information about botulism, visit the USDA's website (U.S. Department of Agriculture) or visit the Botulism pages on the CDC's (U.S. Centers for Disease Control) site.
Salmonella - Salmonella can be killed by boiling (actually if we were using meats, they would have to reach an internal temperature of 160 degrees F, while fresh ingredients only need to reach around 140 degrees F). Use a candy thermometer to test your preparations or employ some extra heat and simmer them.
CDC. "Facts about Botulism." 10/6/06. 8/9/11.
About Salmonella. "Salmonella." 8/9/11.
USDA. "Salmonella Questions and Answers." 5/25/11. 8/9/11.
UAB Medicine. "Botulism." 8/20/07. 8/9/11.
USDA "Preparing and Canning Fermented Foods and Pickled Vegetables."