Brewer's Ed

Bottle and Keg Conditioning: Priming Media and Spunding

Part two of our series on making your best packaged beer

By Nik Allen

Sep 21, 2022

Priming Media: Sugar

Any fermentable sugar will ultimately get the carbonation job done, so long as you still have an appropriate type and amount of yeast in your final product. A long-term fermentation that leaves minimal healthy cells will struggle to carbonate. A bottling strain that is unable to ferment maltose will fail if using wort or dry malt extract. 

If using priming sugar, brewing strains can fully attenuate most simple sugars, like glucose and fructose. In this way, the points per gallon (PPG) of simple sugars can directly work out to the amount of carbonation in the final product. Alternative sugars such as honey, wort, or malt extract, rely on the interplay of sugar composition and the yeast strain’s attenuation range. While online resources can provide a general PPG for these alternative fermentables, the easiest way to confirm this number is to dilute in distilled water and confirm with a hydrometer or refractometer. It’s also important to factor in the volume of liquid priming media when doing these calculations: 10 gravity points of dextrose take up a different volume from 10 gravity points of maple syrup. Once you accommodate for these factors, it is straightforward to add the correct amount of priming media at the end of primary fermentation to achieve the desired carbonation level

Bottle Spunding

Bottle caps

Photo by Adam Wilson on Unsplash

Bottle spunding is a method used to naturally carbonate by packaging beer prior to completion of primary fermentation without adding any priming sugar. While this can absolutely reduce cost and conditioning time, it requires practice and precision to really dial it in.

Let’s say you’d like to package a helles lager at 2.5 volumes of CO2. From the chart above, assuming we do a diacetyl rest at 65°F (18°C), we should expect 1.7 volumes of CO2 in suspension. If we could package the beer with 0.4°P (1.001) left to ferment, the beer would ultimately land at our target carbonation. But there are a LOT of factors that can influence the actual final gravity and resulting carbonation level:

  • Mash temperature

  • Yeast strain

  • Pitch rate

  • Yeast health

  • Oxygenation

  • Grist

Bottle spunding can be a formidable approach, but it is important to account for the range of variability in that final gravity. If you’re happy with a helles ranging from 2.2 – 2.7 volumes of CO2, that gives you some breathing room but not much. It can be best to wait to bottle spund until you are confident in the fermentation profile of your recipe.

Keg Conditioning

Natural carbonation isn’t exclusive to bottle conditioning. For those who swear by the quality of the bubbles produced by secondary fermentation but prefer to serve their beer on draft, the same procedures can be applied to a keg with ease.

Add your priming media to the keg in the same manner as your bottling bucket, ensuring that it is able to dissolve in solution, and leave the keg at room temperature to carbonate. If you are concerned that the seal on the keg will not adequately hold with the rate of carbonation, apply 10 – 15 PSI to the headspace until no leaks are visible. Allow adequate time for the keg to carbonate (dependent on style, yeast selection, and ambient temperature), and chill. Similar to bottle-conditioned beer, there will be sediment at the bottom of the keg. Depending on the flocculation of the yeast strain and the chilling temperature, the beer’s cloudiness and precipitate should diminish after the first pour or two. If greater clarity is desired, a floating dip tube is recommended. It is also possible to cut an inch or more from the dip tube for similar effect.

As mentioned in the previous section, spunding is also a means to achieve natural carbonation without having to add additional priming sugar. If you are able to ferment in a keg, spunding could be accomplished by removing the blow off assembly once you are at the desired intermediate gravity. The added benefit, in this case, is forgiveness in the unfortunate event of over-carbonation; if the beer attenuates further than anticipated, gradually purging the headspace will allow the beer to decarbonate to a desired level. The drawback of this procedure is the loss of any volatile aromatics in the beer (like thiols or esters).

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