Off-flavour in tomatoes

Do you love the flavour of cis-3-hexenal? It's so delicious combined with acid, sugar, and the right balance of other volatile compounds, isn't it? Many prefer it with a bit of 2-isobutylthiazole.

Tomato flavour is a complicated equation. There isn't one "tomato flavour" chemical that gives the tomato its distinctive taste and aroma. For that perfect tomato, the right balance of sugars, organic acids, and somewhere between 30 and 400 volatile compounds need to be in place. Otherwise, you might complain the tomato is tasteless, bland, sour, tastes metallic or has a "chemical" flavour.

The number one consumer complaint involving fresh tomatoes is poor flavour. The final flavour composition of the tomato when it crosses your lips is determined by variety, growing conditions, handling, and storage. Conditions that lead to high sugars and high acids will generally give a better-tasting tomato, but those volatile compounds that finish off that "perfect" tomato flavour and aroma, are critical. Of course, the texture is also important -- and colour and appearance can also influence how the taste is perceived.

Here's a quick (and oversimplified) guide to understanding tomato flavour:


How they affect flavour:

  • Influence taste, intensity of aroma and overall flavour.

What affects them:

  • Variety
  • Light levels during growth
  • Water levels during growth
  • Soil phosphorus and potassium (increased levels may increase sugar content)
  • Soil nitrogen (increased levels may decrease sugar content, flavour)
  • Ripeness at picking
  • And much more


How they affect flavour:

  • Influence sweetness and sourness, taste, overall flavour. Higher glutamic acid concentrations can give "off-flavour".

What affects them:

  • Variety
  • Ripeness at picking
  • Soil nitrogen, phosphorus, and potassium (increased levels may increase acid content of fruit)
  • And much more

Volatile compounds (a few examples)

How they affect flavour:

  • Hexenal, cis-3-hexenal, trans-2-hexenal give "fresh" flavour, but when low, off-flavours may be detected.
  • 2-isobutylthiazole gives "fresh tomato" aroma, but when too high can give rancid, medicinal, metallic odours.
  • 6-methyl-5-hepten-2-one gives "fruit-like aroma".
  • Furaneol is important to tomato aroma.
  • Ethanol and methanol enhance certain aromas and suppress others.
  • Geranial affects overall flavour.

What affects them:

  • Variety
  • Growing conditions
  • Ripeness at picking
  • Storage at cool temperatures (reduces abundance of volatile compounds, therefore changing flavour, but also affects texture)
  • And much more

Perhaps more meaningful to the non-chemist, here is a list of odour characteristics of some of the important volatile compounds contributing to tomato flavour:

  • tomato
  • green
  • fruity
  • floral
  • grassy
  • musty (dirty socks)
  • tomato vine
  • earthy
  • alcohol
  • metallic
  • nutty
  • wintergreen

Clearly, the flavour of any given tomato is very dependent on the right combination of the volatile compounds (with the right balance of fruit acids and sugars). So, if a tomato tastes metallic or like dirty socks, remember that tomato flavour depends on a delicate balance of hundreds of components in the fruit. It's a combination of variety, growing conditions, handling, and storage conditions (plus individual taste preferences) that determine how that tomato will taste on the day it is eaten.

(And you know not to store your tomatoes in the fridge, right?)

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