Edmund Burke, Thoughts And Details on Scarcity, 1795:

" I am greatly afraid that the enquiry will raise some alarm as a measure, leading to the French system of putting corn into requisition."

"My dear departed friend,*74 whose loss is even greater to the public than to me, had often remarked, that the leading vice of the French monarchy (which he had well studied) was in good intention ill-directed, and a restless desire of governing too much. The hand of authority was seen in every thing, and in every place. All, therefore, that happened amiss in the course even of domestic affairs, was attributed to the Government; and, as it always happens in this kind of officious universal interference, what began in odious power, ended always, I may say without an exception, in contemptible imbecillity."

http://www.econlib.org/library/LFBooks/Burke/brkSWv4c4.html

Now Burke was a contemporary politician and critic, not a historian. But the generally gist of the essay suggests that France has erected government owned granaries in order to cut out the middle men, the grain traders, and thus through the government grain would go from peasants to bakers, and thus the profits would be shared by those who do the actual work, peasants and bakers. It was a benevolent instutition but way too much meddling in the market process, according to Burke.

It is well documented that there were several years of disastrous harvests, if what Burke says is right, it is not difficult to imagine that the wrath of the urban poor turned against the government owned granaries.

Adding to /u/DraGulasch 's answer, the idea of state regulation on trading of and speculation in the price of grain is not new. Going back to Louis XIV's reign, then-secretary of state Pontchartrain realized that the growing population of France (in particular in the cities) increased pressure on supply. There was prohibition of export of grains, and there were state attempts to improve the transport of grain within France itself. Finally, there were attempts to prevent middlemen from speculating in "grain futures". They were barred from attending the market outside of limited hours.

Not all these measures were effective, and not all of them were popular. But basically the goals were to encourage the cultivation of grain to bolster supply, through price and trade restrictions.

Going forward to the era of Louis XVI, some of these policies were reversed: in 1764 and 1787 grain export was again enabled and then liberalized. This was an era when the idea of economic liberalization was becoming popular, in particular the treatise of Turgot, Baron de Laune, who became minister of economy. After deregulation of grain, his next goal was deregulation of corn.

Even though his intentions were noble, the liberalization of exports led to rioting, as poor peasants felt they were left hungry while the aristocrats and bourgeois benefited from insrease in exports which led to high domestic prices.

So back to your original question, grain did have quite a lot to do with dissatisfaction with Ancien Régime, but it's deeper than simply hoarding grain, the economic forces were also in play.

Sources:

• Cormac O' Grada, "Famine: a short history," Princeton University Press, 2009.

• Henri Sée, "Economic and Social Conditions in France During the Eighteenth Century,", Kitchener 2004.