How Do You Build a Gluten-Free Beer Recipe Using a Recipe Calculator?

A customer recently contacted us about our 2 Suns gluten-free all-grain beer recipe. After entering the recipe into Brewer's Friend, they noticed that the calculator predicted an original gravity considerably lower than the 1.041 OG listed in our recipe. It was a reasonable question. The recipe contains only seven pounds of grain for a five-gallon batch, most of it rice malt. Using the 20–22 PPG published for rice malt, the numbers don't appear to add up. 

The difference comes from the assumptions used in the calculation. The 2 Suns recipe uses a rising step mash and the exogenous enzymes Ceremix® Flex and Ondea Pro. Our calculations show that the effective extract potential of the specific malts used in the recipe is substantially higher than their published PPG alone would suggest. 

This is an important consideration when building your own gluten-free beer recipes. You can use the same recipe calculators you use for conventional beer, but you need to understand what their calculations are based on and use numbers that reflect the gluten-free brewing process you're actually using. 

Why can a recipe calculator give you a different answer? 

A recipe calculator estimates the gravity of a recipe using the PPG assigned to each fermentable, an efficiency value, and the volume of wort being produced. Some brewing software also makes adjustments to its predicted fermentability and final gravity based on mash temperature. Those calculations work well when the ingredients and brewing process fit the assumptions built into its calculation. 

With gluten-free brewing, the exogenous enzyme combination you're using matters just as much as the mash temperature. Those enzymes play a major role in converting the starch, so the relationship between mash temperature, conversion, extract, and fermentability isn't necessarily the same as it is in a conventional barley mash. The calculator can therefore do the math correctly and still doesn't match what happens in your gluten-free brew. 

How we developed our gluten-free PPG and extract data 

As part of our website migration, we wanted to do more than move our existing recipes and beer kits to a new site. We wanted to standardize the calculations across the entire catalog so that our recipes were using consistent assumptions for extract potential and efficiency. 

We started with the published PPG information for the gluten-free malts we sell. We then incorporated PPG and mash-efficiency values used in production recipe calculations by two dedicated gluten-free breweries, representing more than six years of combined brewing experience. We also collected a sample of published gluten-free beer recipes and ran them through our model, comparing the results with the published recipes to check that the model was producing reasonable results outside of our own recipe collection. 

We then applied the framework across our recipes and beer kits, allowing us to standardize the calculations and create the Beer at a Glance information on the new website, including calculations for both of our recommended exogenous enzyme combinations. 

Published PPG isn't necessarily the number you should use 

PPG, or points per pound per gallon, describes the potential extract from a malt at 100% extraction. For gluten-free brewing with exogenous enzymes, however, the published PPG isn't necessarily the best number to use for recipe calculations. The 2 Suns recipe is a good example: five of its seven pounds are Biscuit 4L Rice Malt, which has an average published PPG of 21 but a calculated effective PPG of 31.08 when using Ceremix® Flex and Ondea Pro. 

Using the effective PPG changes the calculation: 

Biscuit 4L Rice Malt 
5.00 lb × 31.08 PPG = 155.40 points 

Dark Munich Millet Malt 
1.00 lb × 28.16 PPG = 28.16 points 

Caramel Buckwheat Malt 
1.00 lb × 31.00 PPG = 31.00 points 

Total potential: 214.56 points 

At 95% efficiency: 
214.56 × 0.95 = 203.83 points 

For a 5-gallon batch: 
203.83 ÷ 5 = 40.77 gravity points 

That gives an expected OG of approximately 1.041, matching the recipe. This is why the published PPG alone can be misleading. The effective PPG represents the extract potential we expect from the malt when used with a specific exogenous enzyme combination. Efficiency then estimates how much of that potential we can extract. 

Mash temperature can affect the estimated FG, too 

The difference isn't limited to calculating OG. For example, the Grainfather app adjusts apparent yeast attenuation based on mash temperature. Its model assumes the conventional relationship that lower mash temperatures produce more fermentable wort and therefore a lower final gravity, while higher temperatures produce less fermentable wort and a higher final gravity. 

The app uses an Adjustment Slope (%/°F) to determine how much to change the yeast's apparent attenuation for each degree above or below its reference mash temperature. That approach makes sense for the conventional brewing model the calculation was designed around. With gluten-free brewing, however, the relationship between mash temperature and fermentability isn't necessarily the same because exogenous enzymes also influence how the starch is converted. 

Software can therefore produce a mathematically correct estimation based on conventional brewing assumptions without necessarily estimating what your gluten-free beer will actually do. This doesn't make the software useless. It means you need to understand which parts of its calculation apply to your process and which may need to be adjusted. 

How to use the chart for your own recipe 

The chart gives you the numbers you need to build a gluten-free recipe using the recipe calculator you already use. Find each malt in the chart and use the effective PPG for the exogenous enzyme combination you're using. With Ceremix® Flex and Ondea Pro, use the CF+OP Effective PPG and 95% efficiency. With Termamyl SC DS and SEBAmyl L, use the published PPG and 75% efficiency. 

If your calculator doesn't include the gluten-free malt you're using, create a custom fermentable if that option is available and enter the appropriate effective PPG rather than relying on the assigned value. You don't need a special recipe calculator to build gluten-free beer recipes. You just need to give the calculator numbers that reflect the way you're actually brewing. 

That's why we developed this data set in the first place. We needed a consistent way to calculate our own recipes and beer kits during our website migration. In the process, we developed a practical set of gluten-free PPG and extract-potential values that can also help other homebrewers build their own recipes.