Dear Mr. Wizard,
I recently brewed an old ale with an OG of 1.082 and an FG of 1.015. During the last 10 minutes of the boil, I added about 12 ounces (340 g) of maple syrup. The pre-fermentation sample to obtain the OG had a very nice maple aroma and flavor to it. I siphoned the beer into an aging vessel for some long-term storage and am now considering my options. Given the high alcohol content, I want to bottle it and drink it sparingly so that I can see how it matures over time. My intent is to have a low volume of carbonation, say on the order of 1.5 using maple syrup so that I can reintroduce that aroma and flavor. My understanding is that maple syrup is sucrose, and to obtain a CO2 volume of 1.5 in 5 gallons (19 L), it would require approximately 4 ounces (113 g). The final amount in the aging vessel is about 41⁄4 gallons (17 L). What adjustments do I need to make given that I am using maple syrup in liquid form? How should I be measuring this and what amount is appropriate for 41⁄4 gallons (17 L)?
Wizard responds: I assume that the maple syrup aroma faded some during fermentation and that is the reason why you wish to add more maple syrup to the beer at the time of bottling. I’m not sure how you did your calculation and want to walk through a fairly easy method used to calculate priming sugar requirements. Step one is to measure carbonation level in grams per liter instead of volumes. One volume of carbon dioxide is roughly equivalent to
2 grams of carbon dioxide per liter. So in your case you want 3 grams (0.12 oz.) of carbon dioxide per liter of beer and you have 16 liters of beer. This means that you want to get 48 grams/1.7 oz. (3 x 16) of carbon dioxide in your beer by fermenting sucrose from maple syrup. When sugar is fermented by yeast, ethanol and carbon dioxide are produced. Carbon dioxide represents 49% by weight of the sugar. If you want 48 grams (1.7 oz.) of carbon dioxide you will need 99 grams (3.5 oz.) of sugar (48 ÷ 0.49 = 99).
You want to use maple syrup and need to take into account the water contained in the syrup. Maple syrup has standards and most maple syrup has a concentration of 66 °Brix. The Vermont grading standards are a little different and Vermont maple syrup is a little more concentrated. In any case, if you know the Brix of the syrup you are using you can calculate the weight of syrup required by dividing 99 grams (3.5 oz.) of sugar by 0.66 (assuming 66 °Brix) and now know that you need 150 grams (4,252 g) of maple syrup. The 4 ounces (113 g) you refer to is in line with my 99 grams (3.5 oz.) and it looks like our methods are in agreement. The adjustment you need to make requires the 66 °Brix correction factor.
The above can be simplified into the following: Required syrup (grams) = liters of beer * desired carbon dioxide produced during conditioning ÷ 0.49 ÷ 0.66. This equation can be used for any priming problem simply by adjusting the value 0.66 to the sugar concentration of whatever priming sugar you plan on using.
In my experience, many of the nuance aromas associated with whatever special ingredient added to beer is often lost in primary fermentation. If the ingredient is added to the kettle then the volatile stripping can be even more pronounced. We brew an exceptional coffee stout at Springfield Brewing Company (OK, I’m biased, but it’s really delicious) and the best way for us to get the intense coffee aroma in our stout is to add the coffee to the beer after fermentation. I think the subtle nutty notes of an ingredient like maple syrup will certainly be retained by the method you suggest!