The pilot is due to begin later this month across Aldi’s stores in Cheshire, Manchester and Liverpool.
It is being carried out in partnership with milk supplier Müller.
The easier-to-recycle clear caps will replace the green bottle tops on Aldi’s British Semi Skimmed Standard Milk products.
If successful, the trial will be expanded to all the retailer’s Müller-supplied stores, converting an additional 60t of recycled high-density polythene (rHDPE) into food-grade packaging each year.
The used milk bottle tops will be recycled and reused to create new milk bottles.
Aldi plastic and packaging director Richard Gorman said: “We know it’s becoming increasingly important to our customers that their everyday products are environmentally friendly, and we are constantly reviewing ways to become a more sustainable supermarket.
“By trialling clear milk caps, we are making our milk bottles easier to recycle, so they can be turned back into new packaging.”
The initiative is part of Aldi’s efforts to increase its use of recycled materials in its products.
The company has committed to making 50% of all its plastic packaging from recycled materials by 2025.
In May this year, Aldi UK removed plastic shrink wrap from all multipacks of its Corale baked beans as part of efforts to reduce its use of plastic.
This initiative is expected to prevent 78t of single-use plastic from being sent to landfill a year.
The retailer also plans to launch a pilot to remove the outer plastic wrap from its sweetcorn mini-packs at a number of its stores later this year.
Aldi operated 967 stores in the UK as of 7 June this year, 807 of which are located in England.