All three players were expected to be tendered contracts, as Swarzak and Duensing are expected to be important bullpen pieces next season and Plouffe remains the club's starting third baseman.
Major League Baseball's deadline was Monday for teams to offer contracts for the 2014 season for any arbitration-eligible players. Any players who were not tendered a contract before the deadline became free agents.
Duensing, 30, posted a 3.98 ERA with 56 strikeouts in 61 innings last season. It was his first full season as a reliever, as he made at least nine starts with the Twins every year from 2009-12. He made $1.3 million in his first year of arbitration, last year, and is expected to get a raise of about $500,000 to $700,000.
Swarzak also went through his first full season as a member of the bullpen, but he still logged the most innings among any big league reliever. The 28-year-old had a 2.91 ERA with 69 strikeouts in 96 innings as a long reliever. He earned $502,000 and could see a raise between $500,000 and $1 million.
Plouffe, 27, hit .254/.309/.392 with 14 homers, 22 doubles and 52 RBIs in 129 games, and reached the necessary threshold to be a Super Two player and be eligible for arbitration with less than three years of service time. Plouffe has two years and 162 days of service, with the Super-Two cutoff at about two years, 121 days.
His defense improved at third base but he still needs work there and against right-handed pitching. He made $520,000 last season and could make as much as $2 million next season.
Right-hander Josh Roenicke was also eligible for arbitration, but the Twins outrighted him off the roster at the end of the season and he's currently a free agent. Right-hander Vance Worley also would have been eligible as a Super Two player if he stayed on the big league roster the entire season, but he fell short of the necessary cutoff.
Players don't have to file for arbitration until Jan. 14, with the deadline for exchanging salary figures coming on Jan. 17. The Twins prefer to avoid going to arbitration hearings with eligible players, as they haven't been to a hearing since going back-to-back years with Kyle Lohse in 2005-06.
Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, and follow him on Twitter @RhettBollinger. This story was not subject to the approval of Major League Baseball or its clubs.