As an expert sommelier and brewer, I can provide you with a detailed answer to your question about tapping and untapping a keg.
In terms of tapping a keg, the process typically involves attaching a tap or keg coupler to the keg's valve, allowing the beer to flow out smoothly when the tap is opened. This is done while the keg is pressurized, usually with carbon dioxide (CO2), which helps maintain the beer's freshness and carbonation.
Now, when you mention “untapping” a keg, I assume you mean disconnecting the tap or keg coupler from the keg while it is still pressurized. If that's the case, then yes, you can certainly do that without it affecting the beer inside. The beer will remain pressurized and sealed within the keg, so there won't be any spoilage or loss of carbonation.
However, it's important to note that once you remove the tap or keg coupler, you should take care to properly seal the keg valve to prevent any potential contamination or oxidation. This can be done by reattaching the original cap or using a new one specifically designed for keg valves.
In terms of personal experiences, I remember a situation where we tapped a keg for a party but realized later that we needed to move it to a different location. We didn't want to waste the beer, so we decided to disconnect the tap and carefully transport the keg while keeping it pressurized. Once we reached our destination, we simply reconnected the tap, and the beer flowed just as smoothly as before.
To summarize, tapping and untapping a keg while it is pressurized won't have any adverse effects on the beer itself. Just make sure to properly seal the keg valve after untapping to maintain its integrity.