A log book is not necessary, but can serve as a valuable resource. By recording your recipes and procedures, you have something to look back to as a reference. This allows you to replicate your treasures, or modify a recipe that is almost where you want it.
In my log book, I record batch number, style, date started, recipe, when yeast was pitched, date(s) racked (transferred), date bottled and a space for notes.
Here are links to five logs I have created as examples for you to use. They were formatted so that on my Internet Explorer browser they print out as a single, ready to use page. Feel free to print them out to use as is, or to use as a guide for creating one better suited to your methods.
The Brew Log is set up for an extract plus specialty grain recipe, but mash schedules could be listed in the ares for notes.
TheAlt-Wine Log can be used instead of the wine log for country wines and such. The only difference between the two is the name.
Notes on the logbook.
Ingredients: Record the weight or volume of all ingredient as accurately as possible. With this record, it will be much easier to replicate a favorite recipe, or make changes to one that needs work.
Procedure: Recording times, temperatures and other methods used will also help in replicating or improving a recipe. You could also compare the result of different procedures being used on the same recipe, or different parts of a split batch.
Specific Gravity: Recording specific gravity throughout the fermentation process will help you get a feel for the progress of your brews. Like knowing when it is time to rack or bottle. Just in case the abbreviations used are unfamiliar to you, here are some definitions.
S.G. = Specific Gravity. Elsewhere you may also see O.G. = Original Gravity and F.G. = Final Gravity.
P.A. = Potential Alcohol
(v/v) = Percent alcohol or potential alcohol expressed as percent by volume.
Go to HYDROMETER for more details.
Notes: This is where you can record tasting notes, competition results or any other information you think will help you in the future.