The plant manufactures pet food around the clock, turning about 10 tonnes of mostly raw meat products into three tonnes of pet food each day.
The other seven tonnes is wastewater that is mostly converted to water vapour and discharged through exhaust stacks.
The processing is done in five driers in one large room. At the time of the offending between June 12 and October 18, the doors on the third drier were not completely sealed, which allowed "cooking odours" to escape into the processing room.
The Bay of Plenty Regional Council, which prosecuted Ziwi, received 224 complaints about odour from the site between 2008 and 2017.
It issued the company an abatement notice in 2016 over odours, followed by four infringement notices the following year and a formal warning in 2018.
Ziwi made changes in an attempt to address the problem, including spending about $100,000 on deodorising systems, but the complaints continued in 2018 and the council laid charges.
People working near the site told the court they have "felt physically ill as a result of the odour", the judge said.
In September 2020 Ziwi managing director Richard Lawrence said the company had installed further ozone systems at a cost of about $200,000.
The judge said he had been advised Ziwi was relocating its operations to the Hawke's Bay.
In court, he asked when Ziwi would be vacating the site and was told it would be "later in 2022".
In a public announcement in July, Ziwi said its three Tauranga sites would operate until late 2021, when they would close and production would shift to Napier.
Judge Kirkpatrick convicted Ziwi of the charge, writing in his decision that "being in an industrial area is not a licence to discharge offensive odour".
He said it was not for him to "judge the quality of the odour" or work out how the offensive discharges could have been avoided, but accepted Ziwi had made "genuine efforts" to control it.
In addition to a $66,000 fine, he ordered Ziwi to pay a solicitor's fee of $133 and court costs of $130.
Most of the fine will be paid to the Bay of Plenty Regional Council with 10 per cent going to the Crown.
Meanwhile, a sentencing hearing was held in the same court over four other Resource Management Act charges Ziwi has admitted relating to discharges of a contaminant from the same Mount Maunganui site into stormwater systems that flow into Tauranga Harbour.
The charges relate to offending in April 2018.
According to the summary of facts, two charges relate to an early morning incident on April 13 when a Ziwi employee spilt "waste meat product" on to a concrete driveway about 10 metres from a stormwater grate.
He scraped, shovelled and squeegeed up what he could and put it in a grease trap, then hosed down the spill area for about 10 minutes into the stormwater catchpit.
A "yellow discharge" was later seen coming out of an outlet pipe from the Ziwi site.
The council had previously issued Ziwi an abatement notice over wash down contaminants.
On April 19 the regional council was alerted to a "yellow coloured pollutant" described by inspectors as "pungent" in an open stormwater drain near the Ziwi site.
The following day a "milky discharge" was seen in a public drain, with inspectors later finding "meat residue" in a stormwater grate near the site's wash bay where meat was seen defrosting.
According to the summary, "the discharges heightened the risk of microbial pathogens entering the harbour environment, which is a concern to recreational users and consumers of shellfish in Tauranga Harbour".
"No physical impact on or death of aquatic biota in the open stormwater drain or in the coastal receiving environment was observed or measured," the summary said.
Each charge carries a maximum fine of up to $600,000.
Kirkpatrick reserved his decision.
