Fourteen jurors will hear evidence from a toxicologist who found deadly chemicals inside a beef Wellington, after a bombshell day in the trial led to a juror being dismissed.

Erin Patterson, 50, is nearing the end of week three in her triple-murder trial over a lunch she served to her former in-laws in July 2023.

She is accused of deliberately poisoning Don and Gail Patterson, who were her former in-laws, Gail’s sister Heather Wilkinson and her husband Ian.

But she claims it was a terrible accident and has pleaded not guilty to three counts of murder and one attempted murder over Ian, who was the only guest to survive her lunch.

Victorian Institute of Forensic Medicine chief toxicologist Dimitri Gerostamoulos will return to the witness stand on Friday after telling the jury he found toxic chemicals inside leftovers of the beef Wellington.

It came after another expert, scientist Camille Truong, said she found no evidence of death cap mushrooms in initial microscopic testing.

Gerostamoulos said he performed chemical testing of remnants of the meal and found beta-amanitin inside samples of the meat and mushroom paste, which is a death cap mushroom toxin

He also found toxins inside a food dehydrator, which was seized from a tip in the days after the lunch.

Justice Christopher Beale on Thursday dismissed one of the 15 jurors empanelled in late April after he received information they had been discussing the trial with friends and family.

“I was of the view that there was at least a reasonable possibility the information I received was credible,” he said.

The judge told them not to contact the discharged juror and reissued his warning from the beginning of the trial not to discuss the case with anyone outside the jury room.

The trial continues on Friday.

-AAP