Usually home brewers will utilize the basic single step infusion mash. The infusion mash is only really possible today because of two things: fully modified grains and accurate temperature control and measurement. Prior to the availability of fully modified grains and accurate temperature monitoring, a decoction mash was used to reach acid and protein rests. Then a saccharification/mash out step, an infusion step and sparge was possible without actually needing a proper thermometer.
If using a lot of adjunct grains (wheat, rye, oats, etc) it's a good call to use a protein rest. A protein rest has been used for under-modified grains to break down proteins into amino acids that are usable by yeast. My recipe for this brew does not need a decoction mash or protein rest, but since it's the old school way of mashing, we're going to give it a try.
The other reason for using a decoction mash is temperature control. Through a bit of trial and error, the brewer can determine how much boiling of a decoction is needed to get a mash up to the correct temperature . This means with close attention to detail, the brewer can consistently brew without the need of a thermometer (although I will be using one - it would take a few tries to get this right without one). As long as the brewer uses the same ratio of volumes of liquid in mash and decoction boil, with the same amounts of grain and same equipment, the final product should always be the same. [EDIT: I should be more clear here, working without a thermometer would require a multi-step decoction, and we'd need to figure out boil volumes to get our grains to each step]
I'll be doing the simplest decoction mash today - a single step decoction. We'll be doing a protein rest, a single decoction with a saccharification and boil, 30 minute mash and a fly sparge. In the future, I'll be doing a heavily adjuncted (possibly a gluten-free) beer, that will utilize multiple decoctions.
Adjunct: Sources of fermentable sugars other than barley. Usually grains that are not fully modified. Common commercial adjuncts are wheat, rice and corn, others are millet, quinoa, buckwheat, oats and rye. Usually require mashing with barley for proper saccharification.
Decoction: Running's from the MLT that will be heated and added back to the mash
Rest: Period of time keeping the grains and/or decoction at a specified temperature
Saccharification: The process of breaking complex carbohydrates into monosaccarides (fermentable sugars)
Protein Rest: Holding grains at about 122F to break down proteins into usable amino acids.
All Grain Oatmeal Stout
9.5# Organic Crisps Pale Ale Malt
1# Organic Great Western Wheat Malt*
1# Organic Rolled Oats
.5# Organic Briess Caramel 120 Malt
.5# Organic Briess Chocolate Malt
.5# Organic Weyermann Carafa II Malt
.5 oz. Organic Belgian Admiral Pellet Hops @ 60min
.5 oz Organic Belgian Cascade Pellet Hops @ 20 min
.5 oz Organic Kent Golding Pellet Hops @ 5 min
*Wheat isn't really common in stouts (maybe in a Russian Imperial Stout). I added this because I had a pound sitting around, and it kind of goes with the decoction mash.
Volume: 5 Gal
The Single Step Decoction Mash:
The quick and dirty steps of a single step decoction mash for the grain bill:
- Heat 6.75 Gallons of water to 127F
- We calculate this number off of our grain bill and take into account our mash tun. This number will be higher than an infusion mash. We have a total of 13.00# of grain and 6.75 gallons of mash water. This equals about 1.93 Gallons per pound (you could estimate to 2 Gal per #)
- This number will change with your system and the amount of grains/mash water used. Normally you want to drain 30%-40% of the MLT liquid. Essentially we need to pull the correct amount of water, that when boiled and added back into our MLT (which should still be around 120F from the protein rest) will adjust to our mash strike temperature (defined by style, here I'm looking for the mid 150's). This might take some trial and error over a few batches to get your volumes perfect. For our first brew, we'll just have to pay attention, take notes, and adjust our end mash temperature by adding either hot or cold water.
- If you run out of decoction prior to hitting your strike temp, then we need to add more hot water. Remember how much you need to add to get to the strike temperature so that we can adjust for next time. We'd rather not add water if possible, as the thicker the actual mash is, the better extraction we will get.
Volume: 6 Gal
So, using the volumes above, things are looking pretty good. I knew my original gravity would be low. But, using the boiled decoction volume of 3 gallons, I hit a strike temperature of 155F and it held for 30 minutes. Pretty good. I believe the low efficiency was due mostly to my equipment; I did a fly sparge and my equipment is really made for a double batch. If I was using a round cooler, the fly sparge would have worked out better. If I could have lowered my overall decoction volumes and saved more volume for a batch sparge, things would probably have ended up closer to my projected values. Or, I could have ran a batch sparge and attempt to boil off more water (this is probably what I should have done to reach my desired numbers). Each of those methods would add some aspect to the flavor/body of the final product. The main thing here is that the end product will still end up as a good tasty beer. All in all I ended up with about an extra gallon, but was off by about 1% on my ABV.