Using a Bulk Priming Calculator
by buttersd70 on 02-27-2009 at 01:25 pm

Using a Bulk Priming Calculator; the long and the short of it.

Bulk priming allows much more consistent results when compared to carb lollies (yuck) or scoops. The best way to get consistent results with bulk priming is to use a calculator that takes into account the residual CO2 that will be left in solution after fermentation has finished. There are quite a few calculators on the web; the one I use is here. Details of how to bulk prime are in this article here.

The short of it……

The short version of how to use a bulk priming calculator is:

  1. Change all units to metric. That goes without saying.
  2. Enter the desired level of CO2. This will depend on the style of beer you are brewing.
  3. Enter the beer temperature. This is actually the maximum temperature that the beer reached between the end of active fermentation, to the time of bottling. *1
  4. Enter the beer volume. Make sure that you account for any loss that will occur when racking to your bottling bucket.
  5. Select your priming sugar type
  6. Click on calculate.


This will then give you the amount of sugar required to prime to your desired volume.


*1 – By end of active fermentation, I am referring to the end of the CO2 producing cycle of the yeast. For all intents and purposes, this is when krausen starts to subside, and fermentation slows to the point where the production of CO2 is slower than the loss of CO2 caused by the ambient temperature. For practicle purposes, it could be considered to be the last 24 hours of fermentation prior to stable SG.
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The long of it or; the more technical side.

The amount of residual CO2 in solution in a non pressurised situation will change due to several factors; only the first two are of relevance in this situation.
  1. Agitation or nucleation will cause CO2 to come out of solution. This includes shaking, rocking, stirring, and to a degree, racking. Although, for racking that is done whilst cold, I always ignore it. There's getting technical, and then there's getting ridiculous. Same with just moving the fermenter, etc etc. The way I look at it, the normal precautions that you would take to prevent aeration are enough to also make the release of CO2 minimal enough to be a non issue.
  2. Higher temperature will cause CO2 to come out of solution.
  3. Increase in pressure from an external source of CO2 (which will increase saturation, but is discarded, as a fermenter is not pressurized)
  4. Decrease in pressure (i.e., whilst under pressure. Again, this is discarded)
  5. Decrease in temperature, leading to the uptake of CO2 (This is also discarded, because as liquid cools it will reabsorb CO2, but only if there is top pressure as well as a source of CO2.

There is a source of CO2 in this case: the yeast.....they produce CO2 during the fermentation, so whilst fermentation is active, the levels of CO2 present are higher than the normal saturation levels for any given temperature. Once fermentation stops, the excess CO2 leeches from solution and the level of CO2 stabilises at the level which is temperature dependant. In practical terms, having 2 (or3) days of constant hydro readings before crash chilling allows more than enough time for loss of excess CO2, and the stabilisation of CO2 levels at the saturation point for the temperature of the liquid.

So in an example of fermenting for 5 days at a constant 18C (with FG being stable for the last 48hrs), then being crash chilled;

The level of CO2 remaining at 18C is now stable, because you've given it enough time to confirm that fermentation has finished, which allows enough time to desaturate to the level it would normally be at for 18C. The chilling then does nothing in regard to the CO2. If you bottle at this point, then you would use 18C for your saturation level.

If you warm the beer before bottling.......if it is warmed to any point under 18C, then 18C is still used. If it is warmed to a temperature over 18C, then the new temperature would be used....

So, if you are using a priming calculation that takes the residual CO2 into account, you are wasting time and energy, and possibly compromising your calculations, by warming your beer to ambient prior to priming and bottling. You may as well just get it straight out the fridge, and do it straight away. (You also have the benefit that you get less foaming when cold). The exception to this would be if you have had unstable temperature conditions during fermentation, and do not know what the temperature of your beer was at the end of fermentation. However, for a temperature variation of 4C (which is not dissimilar to the difference between reccomended high and low temperature ranges of many yeasts), the difference in carbonation volume only equates to 0.1vol of CO2, which is fairly insignificant, anyway.

Some additional points are:


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Note: As always, you should confirm that fermentation has finished by the use of a hydrometer, to obtain stable readings over several days. Your mileage may vary, and no liability will be accepted. Due care should be exercised when bottling any fermented beverage; failure to take adequate precautions can result in serious injury. Common sense should be used. If in doubt, ask. Open a thread and receive input from others. Or just get a keg system….they're probably less dangerous than flying shards of glass….