Hi Kathleen,
The videos here explain the process well.
This video explains the fermentation process
This explainer is about the Kefir so click here to learn more
This explains how to reculture
In a few words, you simply need to grow the mix of the lactic bacteria and yeast. For this, you need to supply that live mix with the right conditions(food, temperature) for a certain time as in this way control their live cycle. You also need to protect the mix from contamination.
If your previous batch is off, you can start a new fresh one. The fresh things having the requirement to be fresh, so if you start fresh keep it like this. Later when the first batch is ready, you can reculture. We always advise our customers to get a few spoons from the first batch and keep this separated from the batch for consumption, so you will have always some ‘‘mother culture’’ to recultivate a new batch. Using the mother culture as a starter makes things easy as when reculture you can skip the first step of the fermentation which reduces the time for incubation.Every single starter can go off when contaminated.
Please have a look at the video animations, blog or website and post below as a reply if you have questions.