sengsational said:

My quickie research indicates

Mixed results! On the internet? :

I'm looking for the SCIENCE behind the recommendation.

Well, stand back then....

But it really isn't all that sciencey. Carbonation is pretty mechanical...

- The headspace in a corney keg can be measured as a percentage of the volume.
- A Corney is 9" in diameter.
- That means the headspace is about 96 in^3.
- The beer is taking up the remaining 19.5 inches of height for a total of 1240 in^3.
- Thus, the headspace represents 1.57% of the total volume.
- Translated into ounces as a percentage of 5 gallons, the headspace holds
__10 ounces.__

A standard American beer bottle designed to hold 12 ounces of beer is actually a 13 ounce container. A 5 gallon batch makes 53 bottles, ideally. That's

__53 ounces__ of accumulated headspace.

But, WAIT!

...There's more!

Fermented beer has CO2 in it even when still.

This is more on the approximation side of things, but the temperature and handling of a beer effect the amount of standing CO2 in a volume of beer. A beer at 60F will have about 1.1 volume of CO2 dissolved in it. A beer at 35F can have 1.7 volume of CO2.

In a nutshell, the transfer of beer from a fermenter to a keg is smoother than into a series of bottles. Less surface area to volume ratio, and a longer amount of time above the churn point allows the keg product to have as much as 1 full volume more than its bottled counterpoint after transfer.

So, if you're starting with a greater amount of preserved CO2 and don't have as much headspace volume to fill to gain equilibrium, much less sugar is needed.

...Oh, so I'm pretty sure you want a formula or something as a souvenir.

So, here's the formula for dextrose. In fermentation, half the fermentable weight is converted into CO2, the other half into ethanol.

Dextrose as we get it for brewing has a water molecule in it attached to each molecule of dextrose, making it 91% fermentable. I'd say it's completely fermentable, but 91% sounds more scientific-ish for this discussion.

As a bonus, this formula is metric in grams/liter (1 g/l = 0.5 vol)

C = F+ 0.5 * 0.91 * M / V

C: Desired Carbonation level (g/l)

F: Flat Beer Carbonation level (g/l)

M: Weight of Corn Sugar in grams

V: Volume of beer in liters.