The attack occurred on the night of December 28.
Riverland Vintners was established in Monash in 1997. It was acquired by the South Australian Wine Group in 2013.
The winery offers a contract processing service capable of crushing some 25,000 tonnes of grapes.
The 1.2 million litres lost equates to over 1.7 million bottles of wine. However, it represents a relatively small part of Riverland’s total storage capacity of around 34 million litres.
Adelaide’s Advertiser newspaper reports a local eye-witness claiming that the saboteurs had accessed the secure property by cutting through a fence at the rear.
Tyre marks on a nearby dirt road were also visible, the paper noted.
The South Australian Wine Group was formed in 2001 by members of the Harris, Hooper and Koch families to market wine from South Australia’s vineyards.
David Harris is managing director of both businesses.