After picking and crushing mulberries for wine making, I let the berries sit in a vat for about 5 days, stirring at least twice a day.
After this time I strain out the mulberry berries, using three strainers from course to fine mesh, leaving only the mulberry juice to continue the primary fermentation. I do not press out the berries, like with grapes for standard wine production. I find the straining process with mulberries is enough to transfer the juice without adding bitter components that pressing may add.
The transfer process is simple. The berries and juice is removed from the soaking vat, poured through the strainers, then into the new primary fermentation vat. The process can be time consuming, however, as the finer strainer mesh has to be cleaned frequently as it gets clogged with fine sediment.