Why and how to make a yeast starter?
For bigger brews or worts with a gravity above 1.050 the use of a yeast starter is recommended. The quantity of the yeast cells is crucial for the quality of the beer. Most brewers use far too little yeast. This can result not only in incomplete fermentation, but also in abnormal taste and a higher chance of infections, which are often the consequence of yeast ‘undermanning’. Hence it is a good idea to make a yeast starter.
This isn’t that difficult: dissolve 50 grams of malt extract in 500 ml water and add 5 g of yeast nutrient or nutrivit. Boil for 5 minutes and then pour into a thoroughly cleaned and disinfected container (glass Erlenmeyer flask or similar), close tightly with a wad of cotton wool and allow to cool.
When it’s cooled, add the yeast and aerate well (preferably with a sterile air filter and a pump). Keep the container, closed with an airlock, at a temperature of 21 to 26 °C during 12 hours (the yeast will continue to multiply). Your yeast starter is ready for use (or for further multiplication). Add the starter to the wort. If you cannot add it directly, put it in the fridge for the time being. Take the yeast starter out of the fridge a few hours before use so that it can graduately warm to room temperature before being added to the wort.