World grain reserves are at their lowest level since records began in 1960, and U.S, reserves are the lowest since 1948.
These tight stock levels are causing grain prices to be highly volatile. In normal years, prices tend to change by small amounts, rerely more than £1/tonne in one day. This year, prices on the futures market can go up by £10 one day and then drop £8 the next day.
National governments are responding to this with panic measures. Kazakhstan has frozen grain exports, Vietnam and Argentina are reducing exports through export taxes, Russia and China are introducing price controls and Pakistan and Egypt are rationing food.
Remember, all this is happening when the world still has reserve stocks and there will be enough grain to last till next harvest, so what will happen when a real shortage happens and there is not enough to go round
The answer is that it will be every man and every country for themselves. Big exporting countries will ban exports, farmers and grain traders will hang on to stocks, ordinary people will hoard food and supermarket shelves will empty in the panic. Countries that traditionally import a large proportion of their food will really strugle unless they have something like oil to barter with.