Why pickles last

The idea

High concentrations of salt or sugar prevent microorganisms from growing, so they act as preservatives.

Pickles and murabbas

A cut tomato left outside rots within days. But pickles and murabbas stay good for a long time. They have salt or sugar added, with spices.

Why do microorganisms not infect pickles and murabbas?

• The salt or sugar does not let them grow
• Microbes dislike the colour
• Pickles are too hard for microbes

Three jars of tomato

Add nothing, a lot of salt, or a lot of sugar to the cut tomato. Leave each jar for some time.

Preservatives

A high concentration of salt or sugar does not let microorganisms grow, so salt and sugar act as preservatives.

• What is added | What happens to the tomato
• Nothing | Microbes grow: the tomato rots
• A lot of salt | No growth
• A lot of sugar | No growth

Notes

A high concentration of salt or sugar prevents microorganisms from growing, so they act as preservatives.

Check yourself

Which of these act as preservatives?

A cut tomato with nothing added is left outside for days. What will you probably see?

Why are salt and sugar called preservatives?

• A high concentration of salt or sugar — correct. Yes. They do not allow microorganisms to grow.
• Water. Water does not stop microbes from growing.
• Nothing at all. Without a preservative, microbes grow and the food rots.
• A powdery, cotton-like growth — correct. Yes. Microbes have infected it.
• The tomato stays fresh. Without a preservative, microbes grow on it.
• Salt crystals appear. No salt was added, so none will appear.
• They do not let microorganisms grow, so food stays good for longer — correct. Yes. That is what a preservative does.
• They kill the taste of the food. A preservative is about microbes, not taste.
• They make microorganisms grow faster. The opposite: they stop microbial growth.