Giant Hershey's Kiss chocolates are seen on display in a shop in New York City.

With Amazon looming, upstarts nipping and private-label brands burgeoning, Big Food doesn't have time for the small deals of yore. Large-scale mergers and acquisitions are back, as Big Food prepares to make bold moves in response to industry pressures.

On Monday, Campbell Soup announced plans to buy snacks company Snyder's-Lance for $4.87 billion. Hershey announced plans to buy SkinnyPop's parent, Amplify, for $1.6 billion.

Both are the companies' largest acquisitions to date.

The number of U.S. food and beverage deals and their valuation multiples are at record levels, according to data dating back to 1995 from Dealogic. These deals are fetching an average value of 25 times enterprise value to EBITDA.

The steep premiums are in part because there are so few companies that are both growing and large enough to make an impact.

Acquiring companies of scale in more growth categories such as snacks gives Big Food a chance to play within its tool-set: managing brands larger than $1 billion. It helps the larger companies maintain leverage with increasingly pressured retailers.

Snacks, meanwhile, is one of the few categories that food brands have been able to revive through innovation and marketing, like fewer ingredients and clearer packaging.

Snyder's-Lance had sales last year of $2.2 billion. Amplify rang up $270 million in sales last year. Skinny Pop is currently No. 2 in ready-to-eat popcorn. It will be Hershey's sixth-largest brand.

That scale appealed to Hershey.

"At Hershey, we run a portfolio of scaled, iconic brands, and we do that exceptionally well ... as we looked at Amplify, we saw an iconic brand with scale. Scale is a real enabler to catapult us to success," said Hershey CEO Michele Buck in an interview with CNBC.

Tostitos and Lay's owner PepsiCo, the country's largest snack maker, regularly commands profit margins in excess of 25 percent, according to IBISWorld. By comparison, snack-food manufacturers averaged a profit margin of 7.4 percent this year.

Pressure on Big Food to boost growth is not new, but it is increasing. The spree of 3G-style cost-cutting over the past few years has left little obvious fat left to trim. Food retailers are moving online, a channel that no longer offers yards of shelves to promote iconic products. Amazon and European grocers like Lidl are expanding their private-label presence in the U.S., appealing to millennials who care more about price than they do brand.

The recent spate of deals is a far cry from the bolt-ons and investments that proliferated over the past couple of years. Big Food has gobbled up small snack brands such as Enjoy Life, BarkThins and Sahale Snacks. It has poured money into venture funds, hoping to stay close to the pulse of innovation.

Companies have struggled, though, to convert their small acquisitions into brands or platforms large enough to make an impact on their top lines. It is difficult for large companies culturally and structurally to devote massive resources or attention — such as prime shelf space — to still tiny brands.

"There is the inherent difficulty of allocating resources away from billion dollar brands to those generating less than $100 million in revenue," said Todd Lachman, President and CEO of Sovos Brands.

Despite corporate venture investments, blockbuster innovations — including Kind bars, Siggi's yogurt and Bai Brands beverages — are still coming from outside these venture funds.

"It hasn't gotten any better for big food companies, and finally the lights have gone on: We need to do something," said Nicholas Fereday, executive director of food and consumer trends at investment bank Rabobank.