Optimising flavour in mint

Whether you grow peppermint or spearmint, there are numerous factors affecting the flavour in your mint.

Our top recommendations for maximising flavour in mints are:

• Maintain a consistent daytime temperature of about 23°C, where possible
• Use supplementary lighting to artificially increase day length
• Harvest when plants are fully mature but before flower initiation
• Post-harvest, store in temperatures of 2°C
• Avoid stress conditions, such as high UV exposure or water deficit

Mint grown in the UK is primarily one of two species: peppermint (Mentha x piperita) and spearmint (Mentha spicata). Peppermint is a sterile hybrid of spearmint and water mint (M. aquatica), and has a different profile of volatiles from either parent. In this guide, we’ll look at fresh cut and potted spearmint and peppermint.

In the UK, mints are typically field-grown from early spring to November.

The taste of mints is comparatively simple, as it’s mainly governed by a few compounds produced mostly by specialised glands in the leaves and elsewhere in the plant. Leaves are the greatest source of volatile flavour compounds in mints.

The characteristic flavour compounds of peppermint are menthol and its derivatives, which give a cooling sensation and the typical mint aroma. In spearmint, the main flavour compounds are carvone and eucalyptol, which also combine to give a cooling sensation and the fresh minty flavour associated with spearmint. With both mints, there are hundreds of minor flavour components that can alter perception of flavour.

There are a number of growing factors that affect the flavour of mint, each of which you can influence, to ensure the best flavour for the market you’re supplying. Here’s what you can do.

Maintain consistent growing conditions throughout production, avoiding stress from sources such as water deficit, intense lighting or UV exposure. Good practice for plant growth will result in robust plants with a typical flavour profile. 

Research the ideal variety for your production method and customer, as menthol content varies and different varieties respond differently to the environment. 

Fertilise with nitrogen to ensure a good flavour and to maintain yield. Note that in spearmint, excess nitrogen fertilisation increases total essential oil yield, but negatively impacts the overall flavour quality Micronutrients should be monitored to maintain high quality. Manganese is the micronutrient most positively correlated to production of flavour compounds, while cobalt and heavy metal ions have been found to reduce the levels of menthol. Reduced phosphorous levels are associated with higher levels of menthol in mature leaves, but also higher levels of off-taste in young leaves.

A research study reported on the use of arbuscular mycorrhizae Glomus etunicatum, in both peppermint and spearmint. Its use lead to higher levels of menthol, higher water retention and increases in total nitrogen, boron, zinc, copper, manganese and better growth, more leaf mass and higher photosynthetic rate. The effects were greatest in poor quality soils.

Ensure sufficient irrigation. Mints do not respond well to water deficit, with significant reduction of biomass and oil content.

As mint is often field grown, environmental conditions such as weather and aspect will affect the light quality, as will the season. Provide shading where possible, as this leads to preferred chemical profiles. If you grow in glasshouses, a short period of supplementary LED lighting may be beneficial for peppermint.  Its ideal light conditions are low blue light, or higher UV-A. A high UV-A:UV-B ratio elicits a shade response, ideal to mints.

A research trial reported that long days are preferable, as plants grown in these conditions (up to 21 hour days) had the highest oil content and biomass yield. Approximately 12 hours lighting period is the minimum required for healthy crop development. Glasshouse growers can extend the day by using supplementary lights.

Maintain a temperature of about 20–23°C. In the summer months, temperatures may exceed this, particularly in glasshouses, and this can be detrimental to flavour. For potted glasshouse production in winter, heating will promote growth and essential oil production.

Harvest when plants are fully mature, but before flower initiation. In peppermint, the majority of leaves should ideally be at least 12 days old, as this is when menthol production starts. Spearmint leaves also have higher content of the most relevant flavour components as the plant matures, though mature leaves of both species have lower oil content overall.

Flavour in crop grown early or late in the season is less favourable, especially after repeated cuttings. It’s common practice to maximise shelf life by harvesting early in the day, while there is less field heat. However, by the end of the day, sugar content is higher, which is beneficial to flavour and may also help shelf life, if properly cooled.

After harvest, handle with care to minimise degradation. Remove field heat and store at 2°C after harvest, using polyethylene covering, to reduce water loss. We recommend modifying the atmosphere to increase carbon dioxide and reduce oxygen levels.