There has been a lot of debate and discussion amongst homebrewers, beer writers, and beer experts about the need for Decoction Mashing as opposed to just Step Mashing and single infusion. It does seem that the majority of the opinions are that the older Decoction Mashing method is no longer necessary due to the improvments in malting technology and process. I've never thought Decoction Mashing a necessary process to produce good lager beers but I've always wondered if it would yield a noticeable improvement.
So I decided to experiment. I brewed two identical batches of Bock beer. First here are the recipes for 5 gallon batches. The recipes for both the step mash version and decoction mash version are identical and consist of:
10 pounds of Vienna Malt
3 pounds of Munich Malt
1 pound of Caramunich II Malt
This grain bill will yield what would be typically thought of as a Dopplebock (i.e. double strength Bock)
I used Hersbrucker hops in noticeable but not significant amounts. I also used the Weihenstephan powdered yeast know as Safale W34/70. I used this yeast as I have found it to be very reliable and consistent.
Both versions I did an initial hot water infusion to start the mash off at a protein rest at around 122-128 degrees. I let both rest at that temp for 30 minutes. Using near boiling water I infused the Step Mash version to bring the temperature up into the high 140's. On the decoction mash version I did a thick decoction (this involves boiling 40% of the thickest mash for about 10 minutes after a gradual temperature increase through the 150 degree range). After resting in the high 140's (saccarification temperature) I infused more near boiling water into the step mash version to bring it up to a mash out temperature of high 160's and did a thin decoction on the decoction version to do the same.
Both batches underwent a 1 1/2 boil with Hersbrucker hops added with 60 and 30 minutes to go in the boil. I used a whirlfloc tablet for clarification in each.
Both batches came out with a starting gravity at exactly 1072. I was quite pleased that both would be starting their primary fermentation at the exact same gravity.
Both batches underwent a primary fermentation at around 55 degrees for 2 weeks.
They are now both lagering at around 36 degrees in the lagering tank in secondary carboys. They will remain in this state for 2 months and then I'll have some friends over for a blind taste test.