Reaching a Target Original Gravity

Once you have decided what kind of beer you want to brew, you will be able to determine what ingredients are necessary to meet the taste, color and body characteristics of that style. For example, peat-smoked malt may be appropriate for a Scotch ale, but it would certainly be out of place in a Witbier. Once you have determined what ingredients are appropriate for your beer, the next step is deciding how much of each ingredient to use. This is a crucial step in recipe formulation as each of the ingredients used adds a certain amount of specific gravity to the beer. (You may even be required to do a little math!) The key here is making sure your beer comes as close as possible to the target original gravity of your selected style.

The first step is knowing what original gravity you are shooting for in your beer. Next you'll need to know how much gravity each ingredient in your recipe will lend to you beer. Finally, you adjust the amount of each ingredient in your recipe to make sure you not only provide for the target original gravity but also meet the desired flavor, color and body characteristics of your chosen style.

As stated above, each malted grain or sugar used in brewing the beer will add to the specific gravity. (NOTE: Unmalted specialty grains are non-fermentable, so while they may contribute to the original gravity, they will not be fermented to create alcohol.) The important part here is knowing how much gravity each ingredient will add. There is no secret to this. We need a chart. Below is a list of common grains, malts, sugars and adjuncts and the amount of specific gravity they will add to the beer. The gravity for each ingredient is based on 1 pound of the ingredient in 1 gallon of water. Needless to say, doubling the amount of ingredient will double its gravity in 1 gallon of water. Likewise, 1 pound of the ingredient in 5 gallons of water means you'll need to divide the stated gravity by 5 to tell you how much gravity that ingredient will add. Use your head - it's common sense.

Extract Brewing

Now that you know how much gravity 1 pound of each of your ingredients will add to 1 gallon of water, it's time to make adjustments in order to reach the desired gravity. Whether you are using extracts or whole grains, there are simple formulas you can use to determine how much to use. For dried malt extract, use the following formula:

Therefore, if you are brewing a simple pale ale, which (as you know from the the Beer Style Guidelines page) has a target original gravity around 1.050, the formula will look like this (where "X" is our variable - the amount of DME to use):

Therefore, you will need to use a little over 5-1/2 pounds of DME to reach your target gravity of 1.050 if you are brewing a pale ale. A similar formula exists for malt extract syrup:

If you are brewing the same pale ale as above, the formula will look like this:

Therefore, you will need about 6-3/4 pounds of malt extract syrup to reach your target original gravity of 1.050.

All-Grain Brewing

A similar formula exists for all-grain brewers. Again, refer to the chart above to determine the specific gravity of the grains you are brewing with. The only additional piece of information you will need is the efficiency of the mash. Most homebrewers mash at around 65-75% efficiency. For the sake of simplicity, we will assume an efficiency of 70%. Non-mashed fermentables, such as honey, are 100% efficient. The all-grain formula is as follows:

Again, we will used the target gravity of 1.050 and we will assume that we're brewing with American 2-row pale malt, which has a specific gravity of 1.037. Plug in the numbers and the calculation looks like this:

Therefore, you will need approximately 9-1/2 pounds of malt to reach an original gravity of 1.050. Needless to say, the more efficient your mash, the less malt you will need to reach your target original gravity. Pretty simple, huh? Too bad your recipes include more than the base malt or extract.

Multiple Ingredients

The calculations become slightly more complicated when you are adding several different ingredients into one batch of beer. For example, for the pale ale extract recipe we discussed above, you may want to add 1/2 pound of crystal malt as specialty grains, malto-dextrin for body and mouthfeel and Irish moss as a fining agent. Well, we know from our chart above that Irish moss does not add gravity, so we can ignore that in our equations. But what about the crystal malt and malto-dextrin? When combining different fermentables in your recipe, simply divide your target original gravity by the percentage you are allocating to your list of ingredients.

For example, assume we're still shooting for a target original gravity of 1.050, and you want to use half malt extract syrup and half DME for whatever reason. Since each ingredient must contribute to no more than 50% of the total gravity. Based on the calculations we did above, we know that 5-1/2 pounds of DME are needed to get to an original gravity of 1.050 and 6-3/4 pounds of syrup will produce the same results. Divide those amounts by their representative percentage in the recipe and you will figure that you need 2-3/4 pounds of DME plus roughly 3-1/3 pounds of syrup to reach the target gravity of 1.050.

The same concept applies to all-grain brewing. Simply use the all-grain formula rather than the extract formula.

Reaching a Target Alcohol Content

Suppose the most important thing to your beer is that it reach a fairly specific alcohol content. Or maybe you want to clone a beer, but the only thing you know about it is the alcohol by volume (ABV) percentage. Many beers list their ABV right on the label. There is a way to determine how much extract to use if all you know is the ABV. If you are using DME, simply divide the ABV by .84. If you brew with extract syrup, divide by .71. The result is the approximate amount of extract you will need to reach your target ABV. The formula looks like this:

Assume for this section that you are brewing a barley wine and you want the alcohol content to be approximately 10.0% ABV. Simply divide 10 by .84 (or .71) and you will know that you need approximately 12 pounds of DME (or 14 pounds of extract syrup) to reach your target alcohol content.