Why food lasts: drying, pickling and fermenting

Food goes off because moulds, yeasts and bacteria (microbes) eat it before we do. Like all living things, microbes need water, warmth, food and the right conditions. Take one of those away and food lasts much longer.

Drying

Microbes can't grow without water. Dried apple, fruit leather and jerky last for months because most of the water is gone. Fresh apples are about 85% water. Māori dried kūmara, shellfish and fish in the sun, over embers, or on hot rocks in geothermal areas like Rotorua.

Pickling

Most harmful bacteria can't survive in strong acid. A pickle soaks vegetables in vinegar, which is sour because it contains acetic acid. The sourer the brine, the safer the pickle.

Fermenting

Fermenting uses good microbes to beat the bad ones. When you salt cabbage and pack it under brine, lactic acid bacteria that live on the leaves start eating the sugars and making acid. The acid turns cabbage into sauerkraut or kimchi and keeps other microbes out. Yoghurt, sourdough, soy sauce and rēwena bread all rely on fermentation. Rēwena's potato starter, or 'bug', is often kept going in a family for years.

Storing

Some foods last because of where they're kept. Rua kūmara were storage pits dug into free-draining slopes. They stayed cool and damp, so kūmara didn't dry out or rot, and some could be eaten through winter while others were kept to plant in spring. Tītī (muttonbirds) were cooked, packed into pōhā made from kelp, and sealed in their own fat to keep air out.

Old and new

All of them use the same idea: change the conditions so microbes can't win.