The left-hander whacked his fourth century in just his seventh match for the province yesterday.
Only two other batsmen have scored four centuries in a first-class season for the Volts - Otago greats Craig Cumming and Glenn Turner, and they both achieved the feat twice.
Ryder (100 not out from 120 balls) had to share some of the limelight with Aaron Redmond (108), who also posted a century to help Otago reach 271 for three declared in reply to Central Districts first-innings tally of 307.
At stumps, Central was 359 for three in its second innings and leads by 395 runs.
Former New Zealand opener Jamie How also found the pitch at Saxton Oval and Otago's depleted bowling line-up to his liking, posting an undefeated 194 and passing his previous high score of 190 not out.
Otago has lost both its opening bowlers to injuries. But charity or not, How will be hoping to add the further six runs he needs to bring up the milestone when the match concludes today.
With so much play lost on the opening day due to poor weather, Otago opted to declare behind in the hope Central will follow suit and set up a target for the Volts to chase.
That deficit is already very demanding but, given the form of Ryder, in particular, perhaps not yet out of reach.
But while Ryder's on-field performances have been exemplary, off the field it is a different story. The 29-year-old is under scrutiny for his decision to have a drink with Black Caps team-mate Doug Bracewell on the eve of the first test against India.
It is not Ryder's first scrape with discipline and New Zealand Cricket is looking into the incident. The national body will not comment further until its investigation is complete.
Otago coach Vaughn Johnson said the Ryder incident had not been a distraction for the team and Ryder had continued as he had all season.
The Volts' biggest problem was finding someone to bowl in the second innings.
Left-armer Blair Soper was running for a ball and tore his hamstring, and James McMillan stepped in a foot hole and also tore his hamstring.
Central has rattled on the runs in their absence.
''Obviously, they are going to set us a tough target but we are going to have to go for it,'' Johnson said.
''But if it gets to the stage where they are asking us to go at five an over, then the game is dead.''
Elsewhere, Auckland will need a special effort on today's final day to claim its match against Canterbury and climb the standings, APNZ reports.
After Auckland declared at 300 for seven, 28 runs behind the home side's first innings, Canterbury went to the close on 295 for four, a lead of 323.
Dean Brownlie (98) was the best of the home side's batsmen, leaving Auckland holding out hope for a sporting declaration early on day four.
For the second straight day, no play was possible between Wellington and Northern Districts.
