If you're making soap, shampoo or any other cosmetic product that uses lye, your goal should be to prepare it as few times as possible during the week. You should be making lye no more than once per day. If possible, you should make it once a week. Making lye for use during multiple days is called master batching. This can be done in two ways. 50-50 masterbatch: Make a 50% lye solution and dilute it to the desired concentration when using it Ready to use masterbatch: Make lye to the concentration you normally use while making soap. Master batching will save you time, make your lye solution more consistent and reduce your exposure to lye fumes.