In those post is a succint list of steps to create a yeast starter for brewing beer. The instructions are adapted from here.
Below are the steps I have adopted for a yeast starter.
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Boil a pint (1/2 quart) of water and stir in 1/2 cup (80 g) of Dextrified Malt Extract. Boil to sanitize.
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Place pot of DME water in cool waterbath.
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Fill a 1/2 gallon ball jar with sanitizing liquid. Shake with top loose to sanitize lid.
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Sanitize the yeast packet and scissors.
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Poor out sanitizer from jar. Add yeast and DME water.
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Screw lid loosely, so CO can escape, but air does not enter.
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Store in a 70 - 80 F area. Disturb the yeast periodically by sloshing the liquid to feed it.
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Allow 12 - 48 hours for the yeast to multiply.