Recently while researching an unrelated topic I ran across widespread consternation concerning airlock suck back. Across multiple blogs/forums and magazine websites the consensus seemed to be that suck back and exposure of the beer to oxygen and/or sanitizing solution while cold crashing was inevitable. The only solution suggested was to continually bleed in carbon dioxide while cold crashing. I would like to share another solution to this problem.
The solution revolves around attaching a small reservoir to the airlock at the end of fermentation to collect expelled carbon dioxide prior to cold crashing, then sucking back on that reservoir during cold crashing. I have tried many iterations of this technique over the years and have found that the attachment of a completely deflated, sanitized mylar balloon towards the end of fermentation just prior to cold crashing and allowing that ballon to fill with about a liter of carbon dioxide, is the best solution. Latex balloons also work but they slightly pressurize the fermentation vessel. This is no big deal even for Glass carboys.
In the past I have tried collecting carbon dioxide at mid-fermentation using a stopcock on the tubing leading to the mylar balloon. This works just fine but requires attaching the reservoir to the airlock, removing it, and then re-attaching at the time of cold crashing. I've also filled the reservoir with carbon dioxide from a tank and attached it to the fermentation vessel prior to cold crashing. Over the years I have come to prefer mylar balloons over latex balloons because the mylar balloons do not pressurize the system. Unfortunately the current mylar balloons have an ingenious closure mechanism (ValvoMatic) that I have been unable to hack and I have only one old-school mylar balloon (sans ValvoMatic closure) left.
I could see this as a commercial application if someone could hermetically attach a small mylar balloon reservoir to tubing that attaches to an airlock. The balloon reservoir could even contain all manner of graphic/text graffiti such as yeast fart saver, suck back stopper, the suck stops here as current mylar balloons have for birthdays and such. I also could see someone developing an airlock with a side arm to attach a reservoir and a three-way stopcock to direct vented fermentation gases out the airlock or into the non-pressurized mylar reservoir for subsequent cold crashing.
For the images below: one shows a mylar balloon attached to a keg used as a fermentation vessel during cold crashing and one image shows a plastic fermentation vessel with an attached ballon just before cold crashing. With the plastic fermentation vessel you can just make out the fact that the lid is slightly domed outward. With the latex ballon and slight pressurization, I have observed that it takes very little ballon filling to counter the volume contraction/suck back with cold crashing. I think this is bc of increased dissolved carbon dioxide bc of the increased pressure.
The solution revolves around attaching a small reservoir to the airlock at the end of fermentation to collect expelled carbon dioxide prior to cold crashing, then sucking back on that reservoir during cold crashing. I have tried many iterations of this technique over the years and have found that the attachment of a completely deflated, sanitized mylar balloon towards the end of fermentation just prior to cold crashing and allowing that ballon to fill with about a liter of carbon dioxide, is the best solution. Latex balloons also work but they slightly pressurize the fermentation vessel. This is no big deal even for Glass carboys.
In the past I have tried collecting carbon dioxide at mid-fermentation using a stopcock on the tubing leading to the mylar balloon. This works just fine but requires attaching the reservoir to the airlock, removing it, and then re-attaching at the time of cold crashing. I've also filled the reservoir with carbon dioxide from a tank and attached it to the fermentation vessel prior to cold crashing. Over the years I have come to prefer mylar balloons over latex balloons because the mylar balloons do not pressurize the system. Unfortunately the current mylar balloons have an ingenious closure mechanism (ValvoMatic) that I have been unable to hack and I have only one old-school mylar balloon (sans ValvoMatic closure) left.
I could see this as a commercial application if someone could hermetically attach a small mylar balloon reservoir to tubing that attaches to an airlock. The balloon reservoir could even contain all manner of graphic/text graffiti such as yeast fart saver, suck back stopper, the suck stops here as current mylar balloons have for birthdays and such. I also could see someone developing an airlock with a side arm to attach a reservoir and a three-way stopcock to direct vented fermentation gases out the airlock or into the non-pressurized mylar reservoir for subsequent cold crashing.
For the images below: one shows a mylar balloon attached to a keg used as a fermentation vessel during cold crashing and one image shows a plastic fermentation vessel with an attached ballon just before cold crashing. With the plastic fermentation vessel you can just make out the fact that the lid is slightly domed outward. With the latex ballon and slight pressurization, I have observed that it takes very little ballon filling to counter the volume contraction/suck back with cold crashing. I think this is bc of increased dissolved carbon dioxide bc of the increased pressure.
