Optimising flavour in coriander

While most studies into coriander flavour have focused on seeds, it’s been shown that there are a few ways you can improve growing conditions to optimise leaf flavour. Our top recommendations are: 

• Avoid or limit environmental stresses, including water and lighting stress
• Promote vegetative growthasthis correlates to strong flavour 
• Avoid conditions that lead to floral transition, such as long days or stress
• Grow in daytime temperatures of less than 24°C
• After cutting, store at a constant temperature of 2°C

Coriander, also known as cilantro (Coriandrum sativum), is grown for the fresh cut and potted markets in the UK. Coriander is used for its leaves, while its seeds are used for spice. There is also a market for oil production. The UK market is primarily driven by fresh herb sales, either pre-packaged cut herbs or live potted plants. 

Coriander plants have been extensively bred and can be categorised in two broad types. One is used for seed production, bolts rapidly and has a high yield of seed with relatively low vegetative material (these are typically used in India and South East Asia). The other type, which prevails in Europe, North America and Latin America, is produced for its leaves, has a much longer vegetative period and is insensitive to day length. 

In coriander leaves, primary metabolites (sugars) are responsible for sweetness and aliphatic aldehydes (fatty acid derivatives) are mostly responsible for the characteristic aroma. Coriander leaves aroma profile contains around 70 compounds, which affect flavour to differing extents, depending on their concentration and sensory threshold. The overall fatty oil content can directly affect flavour, with low oil leaves seen as watery and insipid, but the amount required for a quality herb is lower than in other species. 

Flavour in coriander is dominated by primary metabolites, which are not greatly affected by the environment, but stress conditions do affect growth. Here are the factors you can influence to ensure your coriander crops have the best possible flavour. 

Avoid or limit environmental stresses, including water and lighting stress, as this elicits a defence response in coriander that creates undesirable flavour compounds. 

Choosing the right coriander variety is one of the most reliable ways of ensuring good flavour. Some varieties strike the right balance between creating an economically viable crop and achieving the desirable flavour compounds in the ideal ratios.

Coriander requires similar nutrients to other leafy herbs. Iron, zinc and nitrogen can increase the essential oil content of coriander, but information on how this affects the overall flavour is limited. 

Trials in Egypt showed that spraying coriander plants with salicylic acid and ascorbate increased the total oil content, but it’s not known how this impacts the oil composition or overall flavour.

Irrigate coriander crops as much as necessary, as drought stress is harmful to vegetative growth and will decrease the flavour compounds. Mild water stress may increase pentadecanone, which is said to aid quality, but it’s unknown to what extent the overall flavour profile is affected. 

Use netting to cut light intensity and can be used to manipulate the wavelengths your crop is exposed to. It’s been shown that purple and red netting result in better flavour, while black netting resulted in herbs being rated as having the least typical aroma. A study in Turkey suggests that there may be a benefit to growing coriander in higher light conditions, such as avoiding shade and using supplementary lighting for glasshouse-grown crops. 

Longer days (above 12 hours of light) are beneficial to the overall yield and content of flavour compounds, but choose coriander varieties that don’t bolt under UK summer day length conditions. If you use glasshouses, use supplementary lighting in winter months when days are short. Time of harvest is a factor in maintaining flavour, with crop grown early or late in the season being less favourable. 

Where possible keep growth temperatures in the range of 11-20˚C for optimal flavour profile. Temperatures above 20˚C will result in flavour compound losses.

Promote vegetative growth, as this correlates with strong flavour. Minimise repeat cuts where possible and dispose of plants approaching flower initiation (bolting) to ensure a more desirable flavour. Young, unstressed plants have higher levels of flavour compounds, with multiple harvest cuts from the same plant resulting adverse changes in flavour, so replacing plants regularly can help to maintain the highest quality. Bolting results in a very strong undesirable aroma, even before the crop visibly bolts. 

Store cut coriancer at temperatures between 0-5°C. Coriander aroma is very temperature dependant, and off-flavours will develop within six days of storage at non-ideal temperatures (up to 10°C).

Consumer perception

Coriander flavour is characterised as having celery, sweet, grassy green, salty, soapy, and bitter notes. With field-grown samples described as having a more intense flavour.

Consumers tend to prefer coriander leaves with a more intense aroma and flavour, however bitterness is not preferred. Multiple cuts of herbs from the same plant should be avoided as this will increase bitterness.

Coriander less intense in flavour will be preferred by the consumer that detects soapy notes when eating coriander.