TreeHouse Foods may be the biggest company around here with zero brand recognition. And that's exactly the way its executives and customers like it.

Chances are you've seen its products—soup, salsa, salad dressing, single-serve coffee pods and such—selling under store brands at Target, Costco, Kroger, Jewel and Trader Joe's. There's another reason you've never heard of it: The company doesn't want you to know which products it manufactures, and the retailers don't either. You won't find “TreeHouse Foods” anywhere on the packaging.

But the Oak Brook-based maker of private-label foods is finding it more difficult to hide. Following its $2.7 billion purchase of ConAgra's private-label food business, TreeHouse is the largest producer of store-branded grocery items in North America by a wide margin, with projected 2016 revenue of about $6.5 billion. In 2005, when it was spun off from Dean Foods, its $700 million in sales came entirely from nondairy creamer, cheese sauces and pickles.

Its founders, led by CEO Sam Reed, 69, along with CFO Dennis Riordan, 58, grew TreeHouse through a series of acquisitions—13 overall—capped by the ConAgra deal, which closed earlier this month. Now they face their biggest challenge yet: binding together two similar-sized organizations seemingly headed in opposite directions.

Perhaps their most pressing issue is teaching a gaggle of erstwhile competitors to get along. “Under a branded model, at the time of closing, everyone gets the same T-shirt and baseball cap,” Reed says. “Here, the brand is owned by the customer and among hundreds of brands that we serve. What's required here is an extraordinarily high degree of social cohesion we have to build through the establishment of our culture, set of values and vision for the company.”

TreeHouse has managed to increase sales thanks to new products in the better-for-you segment. The former ConAgra business, meanwhile, has languished because of a lack of investment by its former owner. ConAgra bought the private-label business from Ralcorp for about $6.7 billion in 2013 and took a $4 billion write-down in unloading it to TreeHouse.

“The previous management team was pretty upfront saying they made several mistakes with the business,” says Michael Halen, an analyst at Bloomberg Intelligence. “There may be significant opportunities for TreeHouse to both increase sales and improve margins just by introducing some innovation around that portfolio.”