Let's start with an examination of the differences in the methods of lagering employed for Winterbier and Sommerbier:
Schenk or Winterbier is put into small barrels, holding from 1 to 4 Eimer, Lagerbier or Sommerbier into large barrels holding 20 to 40 Eimer. In the former, secondary, barrel or small fermentation begins immediately, with the latter a bit later. The quicker start of this fermentation in the case of Winterbiers is due to the fact that this is put into barrels, as they say, greener. The bungs are only slightly closed, so that the foam raised by the secondary fermentation can escape. After 8 days, the secondary fermentation of Winterbier is in the main complete, and already perfectly clear; now the bungs are tightened, however the beer still needs to lie for four weeks before being served. Winterbiers intended for later consumption, which have to be lagered longer than one month, the bungs are still not closed tightly at the end of 8 days, but are tightened only 8 days before tapping each individual barrel.
Sommerbier is usually put into barrels by dividing a few brews evenly into several barrels, not filling them up completely and only closing the bungs much later, often after a couple months ago when a white foam has formed on the surface of the beer, after they have been previously filled to within a few inches of the top. The quicker or more firmly the bungs are closed, the faster and more powerful the secondary fermentation, but also the less time such a beer can be kept. The delivery of Sommerbiere, which in Bavaria by law cannot be served before the 1st May, from the Lagerkellers happens only at the early morning at 4 or 5 clock, so no warm air can get into them. In large Sommerkellers the individual sections are often, after being filled, bricked up in order to keep them properly cool."
"Deutsche allgemeine Zeitschrift für die technischen Gewerbe, Volume 2", page 86. (My translation)
Note that Winterbier wasn't lagered for very long, just a month or so. Unlike Sommerbier, which was lagered for several months. Then kept all summer, too. The bit about only moving beer around in the early morning during summer was new to me. Makes sense, though.
I was going to post some pretty tables here. But they'd make this too long. Tomorrow. I'll publish them tomorrow.