I recommend against freezing your starter. In yeast culturing, we generally "wash" the yeast, and suspend it in glycerin, which helps prevent the yeast cells from rupturing (if I recall correctly, the addition of glycerin exerts osmodic pressure on the cell walls. Don't recall whether this reduces the water through the cell wall, or counters the pressure within the cell as the interior water expands - it's been a while). Cells are mostly water, and you know what happens when water freezes, right? Aside from rupturing the cell walls via expansion, the ice crystals formed within can also be sharp enough to pierce the cell walls - even when glycerin is used, freezing drastically reduces the number of viable cells available in the culture. Your starter is no different. Again, as mentioned above, I store my starter through the late spring until the late fall simply by covering it and putting it in the back of the refrigerator. Yes, some yeast is lost to autolysis; however, due to the reduced temperature, the losses by yeast cannibalizing each other are far less than would be had I frozen the starter instead.

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