Hereford Magistrates' Court heard the 35-year-old employee of Tyrells Potato Crisps in Leominster was cleaning part of the machine on 7 November 2012 when his finger caught in the nip point of a moving chain and sprocket.
As a result of his injuries, his middle finger on the left hand was severed just below the first joint. He was off work for two months but returned to work for the company. The injury has affected his ability to grip.
A Health and Safety Executive (HSE) investigation found the chain and sprocket, on an automatic stirrer, was inadequately guarded. A fixed guard was later fitted to the chain and sprocket. Had this been in place earlier, the incident would have been averted.
Tyrells Potato Crisps, of Stretford Bridge, Leominster, was fined £8,000 and ordered to pay costs of £5,000 after pleading guilty to breaching Regulation 11 of the Provision of Work Equipment Regulations 1998.
HSE inspector Tariq Khan said: "The incident was entirely preventable. Tyrells Potato Crisps Ltd failed to ensure that moving parts capable of causing injury and within hand reach were adequately guarded.
"Employers are required to take effective measures to prevent access to dangerous parts of machinery, or stop their movement before any part of a person enters a danger zone."