Maria Pirie, 46, was cleaning the chocolate hopper at Pecan Candy Deluxe (Europe) Ltd’s site in Sherburn-in-Elmet when the incident happened, Leeds Magistrates’ Court heard.
Ms Pirie, who was not fully trained and was cleaning the machine by herself for the first time, moved the stirrer using the control buttons.
Her left thumb was sliced off as the stirrer moved, trapping it between the side of the vessel and the stirrer.
The Health and Safety Executive (HSE) investigated and prosecuted Pecan Candy Deluxe for failing to properly guard the machine’s dangerous moving parts.
Leeds Magistrates heard the incident on January 25 last year could have been prevented by a simple interlocked guard, which the company had fitted soon afterwards.
Ms Pirie’s thumb was surgically re-attached but will never function as before.
Being left-handed, she has had to relearn how to write and has difficulties with everyday tasks.
The court was told the company had been served with an improvement notice by the HSE in January 2012 regarding the guarding of mixers following a visit from an inspector.
Pecan Candy Deluxe (Europe) Ltd, of Moor Lane Trading Estate, Sherburn-in-Elmet, was fined £7,000 and ordered to pay £627 in costs after admitting a breach of the Health and Safety at Work etc Act 1974.
After the court hearing, HSE inspector Rachel Brittain said: “This incident need not, and should not, have happened.
“The company could easily have prevented access to the dangerous parts of the chocolate hopper by making sure it was effectively guarded.
“It did not and Ms Pirie has suffered a painful and lasting injury as a result. Preventing workers from getting too close to moving parts of machinery is vital. Pecan Deluxe Candy had subject to an enforcement notice on guarding before this incident but obviously didn’t sustain the improvements required.
“Too many are injured, limbs are lost and even fatalities can and do happen because employers fail to guard machinery adequately.”