bunch of fresh basil leaves

Herb Science – Where Does the Flavour of Basil Come From?

The other day we bought a beautiful fresh bunch of basil. Whereas you can use the dried version of a lot of herbs in a lot of recipes, I find that basil is almost always best when you use it fresh. It is no use making a pesto with dried basil, or to eat your tomato & fresh mozzarella with dried basil. You need the fresh version, it has such a strong and characteristic flavour and especially smell.

Have you ever thought about what it is that gives basil (and other herbs) its fascinating smells and flavours? Most likely not, so we’ll have a look at the (mostly) chemistry of basil here. There’s a ton to learn.

What is basil?

Basil is a herb, as most of you will know. There isn’t just one basil, there are actually different basil types, all part of the Ocimum basilicum species. Well known varieties are Genovese, Thai, cinnamon or purple basil. They each have their own aroma’s. Genovese is typically used for Italian pesto whereas the Thai version is a bit more minty and spicy. These differences are due to a different ratio of the aroma molecules.

Basil is very closely related to a lot of other herbs such as basil, rosemary, sage, lavender and thyme.

What gives basil its flavour?

Basil gets most of its flavour from the essential oils in the basil. Most of us think of oils as being triglycerides, these are three chains of fatty acids attached to a glycerol molecule. Essential oils though are not triglycerides and are thus very different than let’s say a sunflower or peanut oil.

Essential oils are mixtures of aromatic molecules. For the chemists: common groups are alcohols, terpenes, esteres, ketones and aldehydes. These molecules tend to be quite volatile, meaning they evaporate easily which is why they find their way to your nose.

Extracting essential oils from plants

Essential oils are typically produced by plants. Basil is just one of many examples. The zest of oranges and lemons also contains essential oils, but the composition is very different from that of basil. But it shows there is a variety of plants that can actually make these essential oils.

Essential oils dissolve very well in alcohol, which is why you can use alcohol to extract the lemon zest flavour from lemons & oranges, but also from a lot of other plants.

Extraction is widely being studied as a method to get a hold of these essential oils. Since plants have a short shelf life, extracting the essential oils may help getting the oils to the right people. Of course, you can also just eat the plants that contain the essential oils.

Benefits of essential oils

Researchers have found various potential benefits of essential oils besides their wonderful aroma’s. Some seem to have antimicrobial properties, meaning they can delay the growth of micro organisms. Also, some may be beneficial for our health and have anti-oxidant properties.

freshly made basil pesto
Just one of the many ways to use basil: make a pesto. You could use any type of basil for making a pesto, but they will all turn out different!

Variations of basil

Researchers have done quite extensive work to try and analyze the composition of those essential oils of basil. Through various analysis methods such as gas chromatography (GC) chemists can identify the molecules present in these essential oils. Despite these advanced methods, it is almost impossible to predict the exact concentrations of molecules in basil. There are a lot of reasons for this, we’ll name just a few.

As with most foods, there is a lot of variation between basil bunches to start with. This can be due to their growth conditions (e.g. sunlight or water), harvest methods and storage.

Researchers have also been able to show that the molecules present in the leaves, flowers and stem can be very different from one another. So, if you use these different parts of the basil herb, your final dish may well taste different.

The origin of your basil (Egypt vs. Italy vs. Spanish for instance) will also impact the exact flavour profile and thus which molecules are present.

Main molecules in basil essential oils

Now that we know what essential oils are and that each basil bunch is different, we can have a closer look at the typical molecules present in basil. These are the main molecules that make up the essential oils of basil:

  • Estragole – this is one of the main molecules in basil leaves, it makes up over 50% of the essential oils and is what gives basil its distinct basil smell.
  • Limonene – this molecule is what gives citrus fruit zest its characteristic smell, it is named after lemon. In basil it isn’t presentin as high quantities but it does help explain why lemon juice and basil work so well together when making a pesto!
  • p-cymene – this is also present in thyme and cumin
  • Apiole – is one of the main constituents of parsley
  • Eugenol – has a clove like aroma since it makes up a very high percentage of the clove’s essential oils
  • Linalool – this is commonly used in a lot of perfumes thanks to its pleasant, flowery smell
  • Eucalyptol – as the name says, it is the main component of eucalyptus, but present in a lot of other herbs as well

As you can see, basil is a true mixture of molecules, and there are a lot more than the ones mentioned here. All of these molecules together give the final complex basil aroma. By switching up the ratios of the molecules you will get aroma’s that smell like those of very different herbs and spices, while keeping the fundamentals the same.

Drying of basil

Since the essential oils that make up most of the flavour of basil are quite volatile, a lot of them are lost either during drying of basil or during storage. Nevertheless, fresh basil cannot be kept for long, so drying is a way to at least preserve some of that flavour. Before drying, most of the basil leaf is actually made up of water, which is also why it shrinks tremendously during drying.

You may have noticed that dried basil smells and tastes different than fresh basil. This is because some molecules evaproate more easily and more quickly than others. That means thatthe ratio of all the molecules has changed and thus the flavour changes as well!


Jean-Claude Chalchat, Mehmet Musa Özcan, Comparative essential oil composition of flowers, leavesand stems of basil (Ocimum basilicum L.) used as herb, (2008), Food Chemistry, Volume 110, Issue 2, Pages 501-503,

O. Baritaux, H. Richard,J. Touche, M. Derbesy, Effects of drying and storage of herbs and spices on the essential oil. Part I. Basil, ocimum basilicum L., 1992, link

Á. Calín-Sánchez et al., Volatile composition of sweet basil essential oil (Ocimum basilicum L.) as affected by drying method, (2012), Food Research International 48, 217-224, link

edited by Seyed Mohammed Bagher Hashemi, Amin Mousavi Khaneghah, Anderson de Souza Sant’Ana, Essential Oils in Food Processing: Chemistry, Safety and Applications, 2018, link

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