Before you can build your own homebrew beer recipes, you must know what kind of beer you like. If you have made the style before, or tasted the style before you're on the right track. To formulate a beer recipe you must know the style inside and out. You must know its signature flavors, which ingredients and/or procedures will result in those flavors, which types of malt will give your beer the flavor it's famous for, which hops will give it the bitterness, flavor and aroma you desire, and which yeast will contribute its own special flavors to the style. If you are a experienced brewer, you may already know all the information you need. If not, then a little detective work is needed.
Look at other brewer's beer recipes. You will notice that they vary quite a bit, but that they will probably have a few characteristics in common. Note those common ingredients and processes from these beer recipes and begin to formulate your own preliminary homebrew beer recipe. Read the appropriate section in the homebrew recipe book Brewing Classic Styles by Jamil Zainasheff and John J. Palmer paying special attention to the "keys" to brewing your particular beer style. Click Here to download my recipe database and spreadsheet from the beer recipes book. It will make it easier to find recipes to brew with your ingredients.
For me it's critical to use a good brewing software. My favorite is BeerSmith. The brewing program will have all the information from the BJCP guidelines for your style. It will allow you to enter ingredients, mash schedules, sparging routines, fermentation temperatures and timelines, and priming or kegging volumes. You will see how your beer reacts with changes in malts, hops, yeast changes, and strike temperatures. An image of the beer's color will be shown along with all of the specifications such as SRM, IBUs, expected Original Gravity, expected final gravity, the beer's water to grain ratio during the mash, and percentages of each ingredient in the overall recipe. You will see some type of indication that your proposed beer is either within or outside the guidelines of the style so you can change the parameters which affect that portion of the beer's outcome. It's great to be able to crunch all the numbers to come up with the same information, but for me, I'd rather be brewing my own homebrew beer recipes than calculating.
Using a good brewing program will free up your mind to concentrate on the big picture, the "perfect beer". Your perfect beer includes elements you enjoy most in a great beer. This is where science falls short and art takes over. When you think about your beer, you are not thinking in terms of gravity, bitterness and color units. You are thinking of the gustatory pleasures your beer will give you. In your mind, how does your beer smell? Is it complex or fairly basic? Make a mental note of that aroma. What does your beer look like? Imagine holding a frosty mug of it up to the sunlight. Is it dark and murky with a tan rocky head, inviting you to explore its mysterious depths? Or is it amber and crystal clear with a bright white foamy head that dissipates but lingers on the sides of your glass, hinting at light maltiness and a crisp dry finish? Make a mental note of what the color and clarity should be. Finally with your mind, imagine the aroma hitting your nose just as you bring your beer up to your mouth and it hits the tip of your tongue. You'll notice the flavors derived from the aroma first. They will tease your senses, giving you just a hint of what is to come. Of course your beer will be served at the optimum temperature. As the beer rolls over your tongue and you get your first impression, make a note of your beer's first impression. As the beer floods your mouth and rolls to the back of your throat, you get an impression of body, is it thin and crisp, thick and creamy, or in the middle? Make a mental note of your beer's body or mouthfeel.
What should the base malt be? Did you notice any nuances in your perfect beer that might be produced by changes in the base malt? Perhaps your pilsner needs just a touch of light Munich malt to give it the richness you remember. Or maybe the Old Ale needs more biscuity background that only a Maris Otter or Golden Promise can give. Make those changes now. Take a look at the middle malts in your beer. If you are making a porter, you can't expect much flavor from just pale ale and black patent. It might make a porter to style, but it won't fit your mind's impression of that perfect porter that makes you want to drink three pints.
You may need to replace a little of the pale malt with some aromatic malt in your beer recipe, or a little caramel malt to stay within the style's gravity range and still give you the complexity you remember. You might even consider replacing a large percentage of your base malt with something different, like brown malt, or a pale ale malt to bring out more richness and complexity to an otherwise plain porter. Keep an eye on the color of your beer as it evolves and adjust the recipe to stay within the style's SRM range. There are many specialty grains that will make your beer go from good to fascinating. Try adding oats or wheat for head retention or creamy mouthfeel. There are roasted versions of these grains that add a whole different taste than the normal roasted malts. Or, try roasting your own. Just place your oats on a baking sheet in a 350° F oven, and bake until it starts turning a light golden brown and you can smell the wonderful aromas. You will be surprised at how much more complexity this will add over plain flaked oats in your beer recipe. Check out the section on malts to get an idea of what flavors they can bring to the recipe.
Once you have your base malt and the middle malts on paper, it's time to look at which hops you want in your beer recipes. You probably have an idea of what type of hops you want to use based on the other recipes you have researched. There are times when it is OK to use substitutions, and there are times when only one or two hops will do. Experience is important here. Knowing what aromas and flavors a certain hops will give you is important. If you don't quite know which hops to use in your beer recipes, read the descriptions of those hops in the hops section to get a better idea. Most beer styles originated using the hops grown in the region. Most commercial examples will use these hops and most BJCP judges will expect the aromas, flavors and bitterness to come from those hops.
So if you want to brew a beer true to style and enter it into competitions, use the hops historically used in the style you're brewing. An Octoberfest just wouldn't be right with American citrus flavors instead of the noble hops the style is famous for. It would become a different beer, an American beer. Aim for a balance between the malt flavors and hop flavors or bitterness in your beer.
No matter what you are brewing, you still have to taste the malts behind all the hop flavors. Sometimes homebrewers make the mistake of shooting for the upper end of the style guidelines on not only the hops but malts as well. If you remember your perfect beer having lots of malt complexity and toasty background notes, you probably don't want to shoot for the max IBUs for bittering in your beer recipe. If you remember some nice noble hop flavors and aromas, you won't see this on the brewing program's IBU calculations. It's because the late hop additions won't impact the bitterness much but will make a huge impact on the hop flavor and aroma in the beer. Use your experience and either taste another commercial example of the style or think of the mental notes you made on the hops impact on your perfect beer. You must remember also that hops fade away with time. If you are making a big barleywine with lots of malty sweetness, you will need a lot of hops. If you plan on aging the barleywine for a year or so before you drink it, you have to take into account the fact that you will lose about 1/2 of the hop flavors and bitterness in that year and plan your hop additions accordingly. In my barleywine beer recipe, my IBUs are around 150, way out of the style guidelines, but I know that it will need to age at least 9 months before I want to drink it and I want the American hop flavors, aroma and bitterness to come through. Otherwise you just have an English Barleywine, which is OK, but not if you wanted American.
And now we get to the ingredient that influences flavor the most, but is probably the least understood, the yeast. Look at the yeast strain information in the yeast section and determine which flavors different strains will add to your beer recipes. Try to match the flavors of the yeast with the flavors you developed for your beer. You should have a final gravity in mind based on the guidelines and from the other homebrewed beer recipes.
Plug in the best choice of your yeast and make sure its attenuation will allow you to hit the final gravity. If it doesn't then you may need to make some adjustments in the recipe. There are adjustments that won't impact the flavor much but will enable you to hit your final gravity. Why is hitting the final gravity important? The final gravity determines not only the amount of alcohol and the alcohol derived flavors in your beer, but also the impression of sweetness or dryness, the impression of the beer's body whether it's thin dry and crisp, or thick round and creamy. Sometimes a few points aren't that important, but sometimes they are. Why not give your beer the ingredients and processes it needs to hit its final gravity. By adding sugar and taking away a little base malt, you can increase the beer's attenuation and finish the beer with more alcohol and a little less body. By adding Belgian Candi syrup you can accomplish the same thing but also add some complexity at the same time. Lowering the mash temperature will accomplish the same goal. If you mash your wort closer to 147°F (64°C), the beer will be more fermentable with more short chain sugars making the beer finish drier and more crisp. On the other hand increasing the mash temperature to the 158°F (70°C) range will give the wort more long chain unfermentable sugars and dextrins, making the beer attenuate less and finish with more body and sweetness.
Now it's time to brew your new homebrew recipe. Gather the ingredients, calculate the amount of yeast needed and make the appropriate starter if necessary. Enjoy the process. Just don't forget to relax, don't worry and have a homebrew. Brew your perfect beer recipe and get it fermenting. Hopefully you kept sanitation at the forefront of your mind at all times and hit all your gravities. Ferment your beer to completion and bottle or keg it. Let it age and condition before you sample it. When the time is right, sit back and savor it. Cheers!