PETALUMA (CBS SF) — Grocery shoppers looking for organic milk in Bay Area supermarkets may be out of luck as farmers struggle to keep up with demand.

Demand for organic milk is soaring, but the supply isn’t, leaving stores across the country attempting to keep the shelves stocked.

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It’s not easy for farmers to increase the supply as calves have to be raised to be certified organic, meaning it takes years before they can start producing milk.

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“Raising organic milk consumption means more organic cows and organic dairies, and finding that supply of hay and grain is smaller because those organic farms aren’t out there yet,” Petaluma organic dairy farmer Jennifer Beretta said.

The milking process is controlled too, and the cows require special maintenance and care.

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“We sell all the milk we can make to Clover, and the cows are in the barn two times a day hoping to get six to seven gallons a day per cow,” Beretta said.