Ask Mr. Wizard

Counting Calories: Pastry Stouts


Dan Farley — Skaneateles, New York asks,

I enjoy drinking beer, as in more than one at a time, and I also have been liking many of these so-called pastry stouts that have been popping up around the country. I do try to watch my waistline and am curious about the general method used to estimate calories in beer at home.



This is a fun question considering the source region; Empire Brewing in Syracuse and Cazanovia, NY has been brewing their Skinny Atlas Light since 1994 using water from Lake Skaneateles. Not sure that Chubby Atlas Choco Stout has the same ring to it! Calorie estimation of beer is easy if you know the alcohol and carbohydrate content of the beer in question. Alcohol contains 7 calories per gram and carbs contain 4 calories per gram. The challenge is calculating these values because there is not a direct relationship between the change in gravity during fermentation and the alcohol and carbohydrate in the finished beer. But there are some pretty solid calorie estimating formulae floating about on the web that are helpful for those brewers who want some solid estimates about calories and alcohol without having to invest in laboratory tests.

I feel comfortable with the equations presented by Dr. Gary Spedding in his presentation titled “Empirically Measuring and Calculating Alcohol and Extract Content in Beer with a Reasonable Degree of Accuracy and Confidence” because Gary explains how he derived his formulae. This is a pretty dense presentation to read, but his formulae can be used to write some handy spreadsheets. Gary presented this paper at the 2014 Michigan Brewers Guild technical conference in Kalamazoo, Michigan and posted his presentation at There are other such methods in the homebrewing literature and select those that make sense to you.

The equations that are handy for calorie calculations are the following:

RE (% w/w) = (0.1948 x OE) + (0.8052 x AE)

ABW (% w/w) = (0.8052 x (OE-AE)) / (2.0665 – (1.0665 x OE/100)).

Where RE is estimated real extract, OE is the original extract (°Plato of the wort prior to fermentation), AE is the apparent extract (°Plato of beer at the end of fermentation), and ABW is the estimated alcohol by weight in the fermented beer.

The thing about all of these estimates based on mathematical models is that they have all been developed using lab data from a selection of “normal beers.” Spedding has a note in his presentation stating “[this estimate of real extract based on apparent extract and original extract] is only an empirical observation and applies only to traditionally fermented beers near 65% RDF (real degree of fermentation).” Pastry stouts have a much lower RDF than 65% because they typically require lots of lactose, and estimates about the caloric content of these beers must follow a different path. And for any commercial brewers reading this column, you all should do what is needed to provide accurate values for labeling. The old expression “close enough for government work” should not be provided as a footnote for guesstimates that are supplied on TTB documents. These beer estimating tools for alcohol and calories also give odd results when used for wine and cider because the models were developed using beer.

Now that all of the legal disclaimers have been noted, it’s time to get on with some generalities to address the basic question about calories and pastry stouts. I’m not looking to establish any new calculators that will stand the test of time here, rather I want to illustrate how boosting the final gravity with lactose affects calories in a 12-ounce (335-mL) beer. The table below shows estimated calories in a range of beers that have apparent extract equal to 25% of the OG, and also shows the calories in these beers when lactose is added to boost the final gravity. I have chosen 2 °Plato, 4 °Plato, and 6 °Plato (1.008, 1.016, and 1.024 SG respectively); these figures represent the bump in original and final gravity associated with the lactose addition (the same because lactose is not fermented by yeast). These lactose supplemented brews are certainly bigger than an average brew, but when consumed like a dessert, pastry stouts are not as calorie-rich as an adult-sized serving of frozen custard.

Response by Ashton Lewis.