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? I like mine 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.
At this point, the scientist in me has to point out that all flavours are chemicals, whether from natural sources or synthetic. The flavour of chocolate depends on over 200 chemicals and vanilla over 100.
The number one consumer complaint involving fresh tomatoes is poor flavour. The final flavour composition of the tomato when it crosses your lips has been 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 you perceive the taste.
Here’s a quick (and oversimplified) guide to understanding tomato flavour:
Sugars
How they affect flavour: Influence taste, intensity of aroma, 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
Acids
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
I hope this illustrates that 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 your tomato tastes metallic or like dirty socks, remember that tomato flavour depends on a delicate balance of hundreds of components in the fruit. And it’s a combination of variety, growing conditions, handling, and storage conditions (plus your own taste preferences) that determine how that tomato will taste on the day you eat it.
(And you know not to store your tomatoes in the fridge, right?)