"Beyond reasonable doubt" is a standard of evidence, it doesn't have anything to do with whether the jury needs to be unanimous. They need to be unanimous regardless of the standard of evidence, even for "preponderance of the evidence" (which means that the jury finds it more likely than not -- that the evidence "tips the scale"). If the jury is not unanimous they need to deliberate more until they are unanimous (if they deadlock then a new jury is called and the whole case starts again).