Darling International (NYSE:DAR) investors, rejoice!

Last week, the country's largest publicly traded rendering company quietly announced that Diamond Green Diesel, its joint venture with oil giant Valero (NYSE:VLO) subsidiary Diamond Alternative Energy, has officially begun production.

The plant will be able to turn much of Darling's recycled animal fat, corn oil, and used cooking oil into 9,300 barrels per day of renewable diesel fuel comparable to petroleum-based diesel. Of course, this news shouldn't come as much of a surprise: The project was two years in the making, and Darling told investors recently the plant would effectively allow them to process nearly 1.2 billion pounds of fat into 137 million gallons of renewable green diesel each year. 

That's why, over the last few months, I've twice suggested investors might be wise to pick up shares of Darling before Diamond Green Diesel's operations came online.

Shoulda, coulda, woulda
After all, the stock was reeling in February after the company missed earnings estimates, and this despite the fact Darling CEO Randal Stuewe had just highlighted that, had DGD been running at full tilt last year, it would have generated net income of more than $41 million for both Darling and Valero.

And while that would have only increased Valero's bottom line last year by less than 2%, remember it would have boosted Darling's own 2012 net income by more than 31%. Better yet, had DGD been running at full capacity last quarter, Stuewe said it would have increased Darling's first-quarter earnings per share by more than 37%.

What's more, there's no reason investors should have been particularly impatient, especially considering that this latest announcement fulfill's the company's promise of a "late second quarter start-up and, barring any unforeseen issues, full production during the third quarter."

Even so, now investors should have nothing to complain about as Darling has finally turned its promises into reality.

It's still not too late
What's that, you say? You still haven't bought shares of Darling yet?

As luck would have it, despite rising 5% in a single day after a solid earnings report in May, Darling stock has largely traded flat since then -- even in spite of a recent bullish note less than two weeks ago from analysts at Wedbush, who initated coverage on Darling at outperform with a $23 price target. For those of you keeping track, that's a 21% premium to today's share price at $19.

In the end, when we also consider that Darling's core rendering operations have never been stronger, the stock looks like a steal trading at just 16.7 times last year's earnings and 14.3 times next year's estimates.

Fool contributor Steve Symington has no position in any stocks mentioned. The Motley Fool recommends and owns shares of Darling International. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.