Using a single decoction, calculate the amount of the mash that will need to be heated with a mash in at 122 °F (50 °C). After 10 minutes, transfer the calculated amount of the mash to a separate pot. Heat the pot and constantly stir until boiling. Return the boiled mash to the mash tun and mix with the remaining grain to bring the temperature to 150 °F (66 °C). Allow the mash to rest at 150 °F (66 °C) for 60 minutes. After fermentation, cold condition the beer for three weeks.
To make the eisbock, use 2-liter plastic soda bottles to freeze the doppelbock. Avoid glass to prevent shattering from expanding ice. Just before the beer freezes solid, pour off the beer into another vessel leaving behind the ice crystals in the bottle. When the sides are pressed, there should be some give but the contents should not still be slushy.

Start with approximately 3 gallons (11.36 L) of doppelbock and finish with 1 gallon (3.79 L) of eisbock.