I'm a new home brewer and have made my first batch from a straight 'out-of-the-box' mix from the local brew store. I'm trying another recipe, this one found out of Charlie Papazian's book and there's no indication as to how much yeast to use for the recipe. What do you recommend as a general ratio for 'yeast to brew'? Also, if I were to try a yeast starter, do you have recommendations of ratios in that sense?
Thanks for writing with your question and congratulations on your start in brewing! In regards to yeast ratios brewers use a rule of thumb that you should pitch one million cells per ml per degree Plato (% sugar by wt) in your starting wort. For instance if your wort has a starting gravity of 1.048 you can divide that by 4 to get approximately 12 deg Plato and you would pitch 12 million cells per ml into the cooled brew. For home brewers this level of precision is not really necessary, most homebrew recipes of five gallons (19-20 liters) can be pitched with one packet of active dried brewing yeast or a single live yeast "smack pack". For best results follow the instructions given on the packages but remember to cool the wort to at least 68F (20C) and since yeast initially needs oxygen to grow and reproduce try to aerate your cooled brew either by agitating with a large wisk or spoon or better yet bubbling air through with something like an aquarium pump. The important thing as you continue to brew and experiment is to keep a journal and write down what you have done and the results you got so that you can fine tune your brewing and the quality of your beers. I suggest you also try joining your local homebrew club and talking to others about their experiences and techniques, brewing is a very sociable community and people who brew love to share stories. Happy brewing!