Chapter 4

Why do tomatoes go off, and why does mould appear on strawberries?

Many people think that spoilage and the growth of mould only begin after harvesting. In fact, however, fruit and vegetables are constantly changing whilst still on the plant, and these changes create increasingly favourable conditions for microbes.

From ripening As this process progresses, the fruit’s outer protective layer gradually thins, and the skin and waxy coating become less effective at preventing microorganisms from adhering to and penetrating the fruit. Meanwhile, the plant’s natural defence system also gradually weakens: the levels of numerous antimicrobial and insect-repellent compounds decrease.

These also include substances that may be toxic to humans in larger quantities, such as solanine in nightshades or the bitter compounds found in certain plants.

At the same time the sugar content of the fruit increases, whilst its acid content decreases, whilst the tissues become increasingly softer. These changes result in a more pleasant taste and a better eating experience for us – whilst providing increasingly favourable living conditions for bacteria and fungi.

The greatest danger, however, is posed by the injuries . Following a crack, insect damage or impact, the plant cells„ nutrients become directly accessible. The damaged surface is a veritable ”feast’ for decay-causing bacteria and fungi, which is why the infection can spread extremely rapidly in such cases.

Strawberries, peaches and tomatoes are particularly susceptible to this, as microorganisms can multiply rapidly on them due to their thin skins and soft flesh.

💚 mould It is not only a problem because it causes an unpleasant taste, a musty smell or a mouldy coating. Some species can also produce mycotoxins that are harmful to health.

Occurring on apples Penicillium Some species, for example, produce patulin, whilst other moulds may produce ochratoxin or other toxic compounds. These are heat-stable compounds, which means that cooking or baking does not always break them down completely.

Gardening tip

If for a longer period of time If we want to store our harvest, we should always choose vegetables and fruit that are undamaged, healthy and not overripe.

• For jam and preserves, too, only wholesome ingredients Let’s use it. The heat treatment It destroys the vast majority of the bacteria and moulds present, but it does not necessarily neutralise the mycotoxins they have already produced.

• When making fruit wine or mash avoid using fruit affected by mould.. The presence of moulds and their metabolic by-products can inhibit the alcoholic fermentation of yeast and cause an unpleasant, musty taste and odour in the finished product.

What is worth bearing in mind about the ripening process?

The ripening of fruit and vegetables benefits both us and microbes. The riper and more damaged a crop is, the more easily spoilage-causing microorganisms can multiply on it. Harvesting at the right time and avoiding damage are the most effective natural defences against spoilage.

In the next section Let’s take a look at how the microbes living in the soil not only affect plants but can also have an indirect impact on human health.

Stay tuned – the next chapter is coming!

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