I make my own local millet drink sweetened with malt sorghum. But I want to keep it free from fermentation for weeks. How? I have sorbate but is not working.
There are different ways to stop fermentation. The bottom line is you have to kill the yeast.
A way to do it would be to let it ferment until it finishes and then sweeten it afterwards.
Adding Potassium Sorbate will not stop an active fermentation, but will help the fermentation not to restart when adding additional sugar after fermentation to sweeten the product.
It would be wise to let the yeast die and then siphon it to a new container before sweetening.