Wrexham Magistrates' Court was told on 11 July that an employee at Tomlinson's Dairies was modifying the pipework at the back of one of the firm's plants on the Five Crosses Industrial Estate in Minera when the incident happened on 3 May 2017.
A pneumatic valve opened and the worker, who was covered in hot caustic and steam, sustained 27% burns to his body. He remained in hospital for four weeks.
A Health and Safety Executive (HSE) investigation found the dairy, which was established by brothers Philip and John Tomlinson in 1983, had failed to isolate the plant and pipework before work started.
The family business, which is run from a nearby farm in Minera, relied on informal risk controls, which were longer sufficient for the size of the business.
In May 2017, BBC Wales reported that Tomlinson's Dairies had expanded its cold storage facilities after it received £5m from the Welsh Government, £2m from Finance Wales and £14.5m from HSBC. It also noted that the dairy, which has a turnover of about £45m a year, is the largest milk processing business in Wales.
Tomlinson's Dairies pleaded guilty to breaching s 2(1) of the Health and Safety at Work Act and must also pay £4,267 costs.