Aug 2 (Reuters) - Warren Buffett's Berkshire Hathaway (BRKa.N) said on Saturday it took a $3.76 billion write-down on its stake in Kraft Heinz (KHC.O) during the second quarter, an acknowledgment the decade-old investment hasn't worked out.

Warren Buffett's company reported less than half as much profit in the second quarter as it took a $3.76 billion writedown on the value of its stake in Kraft Heinz as that iconic food producer considers largely undoing the merger that Berkshire Hathaway helped bankroll.

Berkshire Hathaway ( NYSE: BRK.A ) ( NYSE: BRK.B) on Saturday posted a nearly 4% decline in quarterly operating profit, hurt by soft insurance underwriting earnings and a $3.8B hit to its stake in ketchup giant Kraft Heinz ( KHC ).