The man was detained by officers near Tubingen, south of Stuttgart, following information received from the public, police and prosecutors said in a joint statement. A press conference will be held later Saturday.
Police on Thursday had alerted the public to the risk of food being poisoned, saying a blackmailer was demanding millions of euros in cash.
Authorities released surveillance footage of the suspect, then described as being aged around 50 and who was wearing glasses and a white cap, which ultimately led to the arrest.
To press the demand, the blackmailer had poisoned five baby food products and last week alerted police to the store they were placed in, in the southern city of Friedrichshafen on Lake Constance.
The food — which had been laced with ethylene glycol, a chemical found in anti-freeze and brake fluid — was successfully removed.
But it prompted the nationwide appeal for information on the suspect and a warning about further food tampering.
Through the video surveillance of the stores where the baby jars were identified, police were able to obtain images clearly showing the face of the 55-year-old man, who has not been named.