Same lesson, with the figures in motion.
Capturing Wild Yeast
What can you expect?
The prize is a yeast nobody else has, from your own garden or market. But never make your first attempt on a batch you care about: a wild culture often carries bacteria that sour the beer, and you will not know what you caught until it has finished fermenting.
1. The Bait
Create a weak wort (1.020 SG) and boil it with a few hop pellets. Hops are crucial here—they act as a shield against unwanted bacteria (like Lactobacillus), giving wild yeast a head start to take over the jar.
2. The Capture
Pour the cooled wort into a glass jar, stretch a piece of cheesecloth over the mouth with a rubber band, and stand the jar under a currant bush, a fruit tree or at the edge of a hop garden overnight. The cloth lets in whatever is drifting through the air but keeps debris and insects out — the yeast you catch comes from your own neighbourhood. This is the home version of the lambic brewers' koelschip, the shallow open vessel where the wort cools overnight. They only brew in the cold season (roughly October to March), when the air carries fewer of the bacteria that turn beer to vinegar; catch in summer and expect more failed jars. The alternative is to put unwashed, organic fruit or local flowers straight into the wort; the yeast sits on the outside of the skin, not inside it.
3. The Sniff Test
Bring the jar indoors, cover it with aluminium foil and leave it at room temperature for 3-5 days. If it ferments and smells like vomit, feet, or cheese—dump it (bacteria won). If it smells bready, fruity, or like Belgian spice—congratulations, you caught wild yeast!
4. Taming the Beast
Wild captures are always a mix of different yeast strains and maybe some wild mould. To make a reliable brewing yeast from this, use the Agar Plate streaking method to isolate a single, pure, great-smelling colony!