Optimising flavour in basil

It’s been shown that consumers prefer basil samples they describe as ‘intense’, so how do you ensure that the basil you grow has a rich flavour?

Here’s a summary of our top recommendations for optimising the flavour of your basil plants:

• Maintain a consistent daytime temperature of up to 25°C
• Use UV-B lighting and glass filters
• Choose the right basil varieties for your growing conditions and season
• Keep crops well hydrated
• Induce stress responses with sprays of salicylic acid, but don’t limit essential nutrients or water
• Harvest crops when young
• Maintain consistent temperatures of 10–12°C throughout post-harvest storage
• Use oxygen scavengers in storage and transit

Nearly all basil grown commercially in the UK is Ocimum basilicum. However, other species are used in international cuisine and grown in the UK for niche or worldwide markets.

Basil types are typically grouped by their flavour composition. The most significant is European or sweet basil, and other main classes include Reunion and African or holy basil.

The majority of the flavour compounds produced in basil occur naturally as UV and temperature protectants. These are released into the atmosphere in response to the Mediterranean climate, where it is traditionally grown. Light quality and availability are major limiting factors in developing flavour compounds in basil grown in the UK, but there are numerous steps you can take to ensure your basil plants enjoy optimal growing conditions.

Basil essential oil is made up of over 200 different volatile compounds, predominantly phenylpropanoids and monoterpenes. However, up to 85% of this oil is made up of just six main chemicals, and it’s these that primarily constitute the flavour in healthy plants.

The chemical make-up of basil differs with each variety, but oil quality is the main consideration regardless of the type of basil you grow. Volatile oil content affects the flavour, with low oil leaves appearing watery and insipid.

Making changes to the growing environment can have a major impact on the flavour of your basil, and the key is to strike the right balance between affecting flavour and yield. Exposing plants to UV-B light leads to a more intense flavou profile.

Different varieties of basil contain similar levels of essential oils, but the composition and flavour quality of these oils differ greatly. Choose your variety to suit your growing conditions and market. A high linalool/eugenol profile is typical of European type varieties and the preferred type for the UK market; however other types containing cinnamate or estragole as major constituents are considered for niche markets. 

Under-fertilisation limits the plant’s ability to produce flavour compounds. Ensure your basil is sufficiently fertilised with nitrogen, phosphorus and potassium. Nitrogen is most important, as this maximises photosynthetic potential and will improve the essential oil yield and the flavour.

Research applications using treatments such as salicylic acid, jasmonic acid and other growth regulators have been shown to improve basil’s essential oil content and quality. Different varieties respond differently, but it’s worth noting that these treatments may affect other important factors, such as physiology and yield.

Basil needs to be adequately watered to maximise yields. However, you may be able to improve its flavour with mild water stress, which induces an increased concentration of essential oil but this could result in yield losses. 

Basil prefers direct sun. You can alter the duration, intensity and quality of light your basil receives,to change and improve its flavour, by causing more UV protectants to be produced. Glass cuts out considerable levels of UV-B, so glasshouse production can result in a poorer flavour. If possible, alter the available light using supplementary UV-B, high-pressure sodium (HPS) red-blue LED lighting or coloured reflective mulch to improve the flavour of basic herbs. Diffuse glass will allow in more UV-B light, giving a more intense flavour. Avoid shade conditions, which can lead to stem elongation.

You will need to strike a balance between short day conditions, which improve flavour, and long days, which increase yield. Time of harvest is also important in maintaining flavour, with crop grown early or late in the season being less favourable. 

Maintaining consistently high daytime temperatures encourages basil to produce flavour compounds - temperatures between 15-25°C results in stronger flavour. In some cases growing your basil at 25°C results in more oil content than growing it at 15°C. The final two weeks of production are most critical for ensuring sufficiently high temperatures. 

Harvest your basil as young as is viable, as this improves flavour. Plants less than 12 cm in height are preferable for high-quality pesto products, while older plants close to flowering are ideal for oil production because there is a greater content of oil (though the quality is lower).

Harvest when conditions are cool and keep cut basil at a consistent 10–12°C. Minimise heat shock post-harvest, and handle with care throughout the supply chain to minimise degradation. Lower temperatures can cause discoloration and leaf damage leading to changes in flavour, while higher temperatures promote respiration and the development of off-flavours.

Consumer perception

Basil flavour is described as having clove, menthol, sweet, grassy green and bitter notes. Pot-grown herbs are described as having less intense flavour and greener and sweeter notes. Hydroponically grown basil produces a strong flavour.

Consumers tend to look for basil that is more intense in aroma and flavour. However, stronger flavour also gives higher bitterness and this is often disliked by the consumer. Basil with a good balance of cloves, woody and menthol notes tends to be preferred.