Fruit juice

In detail

Fruit and vegetable juices are coloured mainly by anthocyanins, water-soluble pigments that shift colour with pH — which is why blackcurrant, beetroot and berry marks look purple, red or blue-grey depending on what has been put on them. The pigment fraction is usually the easier half. The harder half is sugar, which dries invisible and then caramelises slowly, so a fruit spill that appeared to have been cleaned up reappears as a brown mark weeks or months later, and heat accelerates it. That is the reason every trade procedure insists on rinsing rather than stopping when the colour has gone. The carpet institute puts the whole family on the aqueous-tannin branch — detergent solution, vinegar solution, warm water, spot removal kit, ammonia — with the acidic step doing double duty by restoring the anthocyanin to its more soluble form and by neutralising the alkalinity the detergent leaves. On white cotton an oxygen bleach handles what remains; on wool and silk it does not, because the wool trade advises against both bleach families on protein fibres.

Why

• Fruit juice is explained by pH indicators in stains
• Fruit juice is explained by Classifying a stain by its origin
• Fruit juice is explained by Pigment retention
• Fruit juice is explained by Why old stains are harder

Hacks and claims involving this

• Leaving a stain in the sun to fade it Plausible mechanism, untested in this application