While the upgrade is expected to extend the cheese-making season, it will not create any jobs, site manager Mark Leith said.
Contractors began installing new equipment in the milk treatment area at the end of April and Mr Leith said the site should be on production stand-by in mid-September.
The investment was an endorsement from Fonterra and secured the Stirling site's medium-term future as a strategic cheese manufacturing plant.
The 2001 site upgrade, which took daily production from eight tonnes an hour to 10.5 tonnes an hour, had been a $17 million investment.
While significant, the latest investment of $7.75 million was "an enhancement to the current process".
The result was no new positions were created for the factory, which employs 107 people, he said.
"We would process around 45,000 tonnes a season, but the new equipment means there is potential to grow that."
The upgrade would not increase daily output capacity, but could extend the production season by as much as two months, beginning in early August and ending in May.
The equipment and supporting infrastructure upgrade would allow the factory to produce a reduced-salt cheese which won the International Dairy Federation Award in Austria in April.
The cheese contains about 40% less sodium than normal cheddar and was developed to cater to health-conscious consumers in the UK and Asia. Fonterra was exploring options for introducing the cheese to Australian and New Zealand markets, Mr Leith said.
