Cornelius kegs are metal containers that the soft-drink industry once used to create soda. This is why we also refer to them as soda kegs. However, technological advances eventually made these stainless steel cylinders impractical for the soda companies, at which point they became accessible to homebrew enthusiasts. Now, manufacturers create Corney kegs almost exclusively for this market, and they are an amazing tool, especially for the creation of high-quality lagers and ales.
The “secret” to proper beer fermentation using a Cornelius keg is control of the krausen. Krausen is that foam head that develops during the initial phase of beer fermentation. Because of the small volume, Cornelius kegs provide almost no headspace, so fermenting with unchecked krausen leads to a messy blow-off and other problems. There are several ways to counter this, the use of Fermcap-S being the most common.
Fermcap-S is a unique and FDA approved emulsion of Dimethylpolysiloxane that is incredibly effective as a surface agent. By reducing surface tension, it is able to prevent foam formation during fermentation, but it doesn’t affect head retention of the final product because the filter media, yeast, and vessel walls, absorb all of it during the fermentation process. In a Cornelius keg, you will generally use two drops per gallon when pitching.
It is also important to note that stainless steel makes for excellent fermentation only when it is clean and sanitized. Otherwise, you will notice a sharp decrease in the quality of the product. Therefore, even though this can be a major hassle, clean and sanitize it after every use. This is especially important because the wort, the unfermented malt, is highly susceptible to contamination. The need for sanitization is also a good reason not to use the Cornelius keg for both fermentation and serving.
Although it does add quite a bit of work, we highly suggest breaking all your equipment down to its finest component parts, cleaning them, and then sanitizing them. For best effect, soak parts, especially the Cornelius keg parts, in an acid-based sanitizer. Do not use percarbonate-based sanitizers, at least on the Cornelius keg, because it employs oxygen, which can rouse flaws in the stainless steel.
You can also opt to boil to sanitize or use a combination of the two methods for best effect. Boiling is particularly effective if debris is visible, and if the debris is protein-based, it’s best to use a cleaner in the boil solution. There are many on the market, and most Cornelius keg kits include them. While boiling, move the objects around so that each aspect of the objects has equal exposure. Once done, completely dry each piece and then reassemble the Cornelius keg.
Once you have a completely clean, completely sanitized Cornelius keg, it’s time to transfer the cooled wort into the keg via the main lid opening. At the very least, leave a 0.5-inch of headspace, but novices may want to leave as much as 2 inches. In addition, do not fill the Cornelius keg through its dip tube. It is quite easy for the post to clog from the particulate, at which point you’ll have an incredible mess on your hands.
After you have finished filling the Cornelius keg, add 2 drops per gallon of the Fermcap-S. It is extremely important that you keep the Fermcap-S refrigerated because it will quickly spoil at room temperature. Note that, as mentioned earlier, Fermcap-S will not alter the final product, and if you do not use the proper amount a 0.5-2-inch headspace will result in a blow-off.
One common problem with Cornelius kegs are settling issues with the yeast, which occur due to the vertical shape. Generally, this will only result in problems with clarity, which you can rectify using a clarity agent. However, the better alternative is to drop the fermentation temperature. In other words, refrigerate the Cornelius keg while the fermentation process is ongoing. If you can’t refrigerate, store it outside during cool nights. Don’t worry about disturbing it since that actually increases absorption rate.