Optimising flavour in parsley

Consumers show a preference for more intense flavour in parsley, preferring the aroma to be ‘typical’ and ‘parsley-like’. To ensure this characteristic flavour, the main things to take into account when growing parsley, are:

• Grow under low-stress conditions (though mild water stress may be used without harming the flavour of curly leaf varieties)
• Don’t over-fertilise with nitrogen
• Later cuts of parsley have better flavour than younger plants
• Handle with care post-harvest and store at 2°C

Two main species are grown in the UK: curly leaf parsley (Petroselinum crispum) and flat leaf or Italian parsley (Petroselinum neapolitanum). Other varieties can also be grown for the roots. Flat leaf and curly leaf are different species, with different chemical compositions that mean they can sometimes respond differently to their environment. 

The UK parsley season typically runs from April to November, although modern glasshouse production extends this significantly with supplementary lighting. 

Parsley essential oil contains around 45 different volatile compounds, and consists mainly of monoterpenes, along with other secondary metabolites and some fatty acid derivatives. The majority of flavour comes from hexanal, which gives a green and grassy aroma typical to many herbs. The typical parsley aroma comes from menthatriene and myristicin.

The overall content of these flavour compounds can directly affect flavour, with low oil leaves being perceived as watery and insipid. Concentration of different compounds varies greatly, especially between parsley varieties.

Here’s what you can do to ensure optimal parsley flavour, whether you’re cultivating flat or curly-leaf varieties.

Keep stress to a minimum to maintain the typical flavour profile of parsley. The exception to this is that curly leaf parsley varieties appear to be resistant to water deficit, which can be applied without adversely affecting the flavour. 

Choose parsley varieties suited to your growing conditions. Varieties with a strong aroma are regarded as the highest quality. 

Monitor nutrients frequently and fertilise with NPK and micronutrients. However, don’t over-fertilise with nitrogen, as this can lead to a reduction in flavour. Ideally, use no more than 100 kg/ha of nitrogen per cut, with no more than 200 kg/ha of nitrogen at planting

Plants spaced more closely together show a slightly higher abundance of oils. 

Irrigate normally for flat leaf parsley. Water deficit and mild salt stress can modify the oil content and composition and improve flavour, but only in curly leaf varieties.

Warmer temperatures and longer days lead to a greater concentration of flavour compounds in flat leaf parsley, but a slightly lower concentration in curly leaf parsley. 

Grow parsley at about 25°C, where possible.

Later cuts of parsley are reported to have better flavour than younger plants. More oil is present in parsley on the first cut than in subsequent cuts, but the later cuts are thought to have better flavour composition. However, younger leaves have a stronger characteristic flavour in both curly leaf and flat leaf parsley, while older leaves tend to have higher content in the leaf stem. Initiation of flowering will lead to higher concentration of compounds, but this is associated with a decrease in palatability.

Harvest early in the day when field conditions are as cool as possible. 

Limiting exposure to ethylene through use of chemical blockers such as 1-MCP can prevent the loss of flavour post-harvest, as can storage at 2°C. Parsley is relatively robust in terms of shelf life, with little chemical change seen through a typical shelf-life storage of 12 days.