Each bottle of Kefir and/or Kombucha is ALIVE.
That means that the bottles are not static. The live bacteria and yeast that are inside continue to live on. One aspect of that is that the production of CO2 that makes our drinks naturally sparkling - doesn't stop. As time goes, the level of sugar will drop and the overall bottle pressure will rise.
At all times, the bottles must be kept refrigerated.
Do not forget bottles outside - they risk to be filled in with too much gas and eventually the extra pressure will break the glass and make the bottle explode!
Do not shake the bottles but rather stir them gently to spread the bacteria evenly through out the bottle before serving it.
If a transportation without a cooler has to be done for more then 30 minutes, open the transported bottle and remove the transparent insert, close the bottle with the main cap. Upon arrival, put back the insert and close the main cap to re-build the pressure within the bottle and its sparkling effect. That is the safest. Otherwise, before the trip double check the pressure of the bottles and estimate if it is ok to do not remove the insert - that option is for more experienced users who can judge the pressure of a given bottle! The safest procedure remains still the best procedure!
During a prolonged period of storage - more than 2 weeks - it is advised to open the bottles to release the built in pressure before putting them back for further storage.