Heinz has reportedly replaced free-range eggs with cage-free alternatives in its Seriously Good Mayonnaise as outbreaks of avian flu disrupt supplies across Europe.

The food giant said it could no longer secure free-range eggs in the volumes needed to manufacture the condiment, prompting it to change the recipe.

Heinz quietly announced the switch on its website in March, although it has only now come to wider attention.

It said increasing numbers of free-range hens were being kept inside barns to limit the spread of bird flu, reducing the availability of eggs that can be marketed as free range.

Heinz added that moving to cage-free eggs would help keep its products widely available while maintaining the quality shoppers expect.

Unlike free-range hens, which must be given access to outdoor areas, cage-free birds can remain permanently indoors but are not confined to cages.

The change marks a notable reversal for Heinz, which has promoted the use of free-range eggs in its mayonnaise for more than a decade.

When the brand reformulated its mayonnaise range in 2011, it placed free-range sourcing at the centre of its marketing and highlighted the claim prominently on packs.

Older product descriptions for Seriously Good Mayonnaise also stated that the condiment was made using 100 per cent free-range eggs. The current UK listing instead describes the mayonnaise as being made with “quality ingredients”, with no free-range claim included.

Heinz has not indicated whether it plans to return to free-range eggs once supply conditions improve or whether the change will become permanent.

The move comes as European poultry producers continue to manage the impact of avian flu, with housing restrictions frequently introduced to keep birds indoors and reduce their exposure to infection.

Such measures can affect whether eggs retain their free-range status, placing pressure on food manufacturers that depend on large and consistent supplies for products including mayonnaise, sauces, ready meals and baked goods.

Heinz stressed that the new eggs would remain cage free, meaning the company has not returned to using eggs from hens kept in conventional cages.

Kraft Heinz has previously made cage-free sourcing a central part of its animal welfare commitments. In 2016, the group pledged to move all its North American operations to cage-free eggs by 2025, including those used in Heinz mayonnaise and other sauces.

Sign up here to get the latest grocery and food news each morning