What is a yeast starter and do I need to make one?
A yeast starter is a non hopped wort which is used to increase the quanity of healthy yeast cells prior to pitching. They are simple to make, just make up a 10% solution of spraymalt/water (ie 100g/1 litre), boil for 15 mins, cool then they are ready for the yeast. Important - do not use sugar.
Unlike a standard fermentation, its important to get oxygen into the solution prior to pitching and also while fermentation takes place as plenty of oxygen will allow more healthy yeast to be produced. Therefore do not make a starter with an airlock on it. The easiest way to make a starter is to use a Erienmeyer flask which allows you to make up the starter, boil and cool all in the same container which avoids sterilising a seperate container.
Just simply add the yeast once cooled, cover with some foil crimped around the side and leave to ferment for around 48 hrs. Give the starter a good shake everytime you walk past it to get plenty more oxygen in it. Then once its complete, leave to settle before pitching. This will allow the yeast to seperate from the liquid, which can be poured off before you pitch the yeast.
Starters are only required for liquid yeasts where yeast counts need to be increased either due to the age of the yeast or due to high gravity worts or low fermentation temps (ie lagers).
Making up a yeast starter will decrease the lag time (gap before yeast starts working) of any fermentation and therefore it will not hurt to use a small (1 litre) starter prior to pitching any liquid yeast.