Think you are nearer to 50% extraction at that gravity... assuming that the corn is 0.8 DBFG. Maybe it isn't that high, but could be pretty close. Had you previously calculated the potential of the corn? Was this cracked corn?
The gravity reading will be affected by both the converted sugars and unconverted starches, and I don't imagine they affect the gravity in the same way. One doesn't really get an initial gravity reading with the sake process. If you are confident of the potential of your corn, you could ferment your experiment and then monitor the initial boiling point of the wash/mash. Then you know the ethanol% and as they say, 'the proof is in the pudding.'
'Bubble cap plates are better for batch distillation than perforated plates' - Benjamin Franklin
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