You are looking at wet weight, which is highly misleading. You should be looking at dry weight. > In general terms fresh potatoes contain ~20% dry matter (DM)

You are looking at wet weight, which is highly misleading. You should be looking at dry weight. > In general terms fresh potatoes contain ~20% dry matter (DM) of which 60–80% is starch That's 60-80% by dry weight. I assure you that the types of potatoes eaten in Eastern Europe contain approximately 109% starch by dry weight.