Help me diagnose terrible partial mash efficiency

[scone]

So I brewed (attempted to brew) Denny Conn's bourbon vanilla imperial porter yesterday. I can only do partial mashes (no real mash or sparge setup). I've been doing partial mashes in a 3 gallon stainless steel pot, and I pour the grains through a colander lined with a nylon bag and rinse them gently with 2 quarts of 170F water to "sparge". This has worked very well for me in the past, and I've hit the target OGs of several beers I've done this way. I'm also very new to brewing, and still figuring out the whole mashing business... this is my 7th beer.

Here's the original all-grain recipe:
11 lb. 2-row
2.5 lb. munich malt
1.5 lb. brown malt
1 lb. crystal 120
0.5 lb. crystal 40
1.25 lb. chocolate malt

I converted the recipe into partial mash by removing all the 2-row and using 8 lbs. of LME in the boil. Thus I "mashed" just the munich, brown, crystal, and chocolate malts.

Here's an overview of my process:
I heated 2 gallons of water to 170F, doughed in the 6.75 lbs. of grain (a tad under 1.25 quarts/lb of water), and after stirring for a bit I hit a nice even 156F. I covered the pot and wrapped it in a blanket and left it for 1 hour. After the mash was over I checked the temp. again (after stirring the mash) and I got 148F. Pretty drastic temperature drop but like I said, this technique resulted in fine efficiencies in the past.

I added 2 quarts of boiling water to the mash, stirred it up a bit, and dumped it through my colander/nylon bag into my boil pot, and rinsed the grains with another 2 quarts of 170F water. After this I added the LME and enough water to reach a boil volume of 5.5 gallons. Boiled for 60 minutes, chilled, racked, and topped the fermenter off with about 1.25 gallons of water to hit 5.25 gallons. I stirred like crazy using a drill and my fancy new stainless steel stirring rod.

I checked the OG in the primary (at 72F) after all was said and done and got 1.072. The OG should have been 1.091!! Now, the LME contributed 1.058 points of the final gravity, which means I only got .014 points from the entire mash. That's pretty much like 30% efficiency for the mash... what happened?

I thought the munich had enough diastatic power to convert itself plus the brown malt. Am I wrong? The crystal and chocolate malts don't need to be mashed anyway right? It seems like I got virtually no gravity contribution from mashing 6.75 lbs. of grain, so something is really amiss here. I'd definitely appreciate some pointers for next time.

 

[david_42]

and rinsed the grains with another 2 quarts of 170F water.

Nowhere near enough sparge water. You effectively got your first runnings, which are about half the total sugars. When I do a PM, I sparge with 1.5-2 times the amount of mash water.

 

[scone]

Nowhere near enough sparge water. You effectively got your first runnings, which are about half the total sugars. When I do a PM, I sparge with 1.5-2 times the amount of mash water.

Yeah maybe my strategy is only good with very small mashes.

How do you sparge? Do you lift the grain bag and move it to another vessel to batch sparge, or are you doing something different?

 

[wyzazz]

I do my AG and PM batches using BIAB. With no sparge step, I get around 80% efficiency.

 

[scone]

No more opinions out there? Or is everyone agreed that I didn't sparge enough?

It does seem odd that the BIAB no-sparge crowd gets much better efficiencies doing pretty much the same thing I did.

 

[Austin_]

How confident are you in your thermometer's accuracy? Have you calibrated it? I ask because I use to get pretty crappy efficiency before I bought a new thermometer.

 

[wyzazz]

No more opinions out there? Or is everyone agreed that I didn't sparge enough?

It does seem odd that the BIAB no-sparge crowd gets much better efficiencies doing pretty much the same thing I did.

Yes, not enough sparge water.

Why does that seem odd to you? There is a tremendous amount of water in the kettle when you do BIAB, and most of us that do it crush the beejezzus out of our grain. When I BIAB I also squeeze my grain bag to help extract sugars.

I guess one could also ask what your crush looked like on your grain.

 

[Bobby_M]

In my opinion you have a diastatic power deficiency. Munich has just enough (enzymes) to convert itself. Chocolate, Brown and caramels don't have any. You need a pound or two of the 2 row to help convert and your temp loss didn't help either.

 

[GuldTuborg]

^^^ You beat me to it. Only the Munich has any diastatic power in there, and then only enough to self convert (under perfect conditions). You need to keep at least 1lb of the pale malt in there. It's not really a mini mash otherwise, it's a steep for color and some flavor.

Also, are you sure you added enough LME?

 

[scone]

Thanks for the help everyone!

How confident are you in your thermometer's accuracy? Have you calibrated it? I ask because I use to get pretty crappy efficiency before I bought a new thermometer.

I'm pretty confident. I'm using a Fluke multimeter with a type-k thermocouple. It's overkill I know, but why not if I've already have one, right? I did realize that both my cheapo glass brewing thermometers are off, one of them by 4 degrees!!

There is a tremendous amount of water in the kettle when you do BIAB, and most of us that do it crush the beejezzus out of our grain.

I didn't know that about the BIAB technique. Makes sense though. My grains were crushed by AHS so I'm sure the crush was fine (but obviously not optimized for no-sparge mashing in a bag).

In my opinion you have a diastatic power deficiency. Munich has just enough (enzymes) to convert itself. Chocolate, Brown and caramels don't have any.

Bobby, any idea what this would do to the flavor of the beer? Will I just get a very small contribution from the Munich and Brown malts, and full contribution from the steeping grains (crystal and chocolate)?

Also, I don't fully understand the diastatic power and starch conversion stuff as well as I'd like yet. It was my understanding that chocolate and caramel/dextrine malts don't have anything to convert... am I wrong?

 

[ChshreCat]

Since you're mashing in a pot, you can use your oven to help avoid the temperature drop you are seeing. When you're getting ready to mash in, turn your oven on to it's lowest setting. Once you hit temp in your mash, turn the oven off and put the pot in the oven. The residual heat of the oven will keep the pot from cooling off as fast as it does on the stove top, even with the blanket around it.

I usually stirred my mash about halfway through and would turn the oven back on to it's lowest setting for 30-60 seconds just to heat the elements up and re-warm the oven a little.

I did this with every brew until I moved to a converted cooler for my partial mashes and it works GREAT. I'd only see a couple degrees difference between the start and end of my mash.

 

[Denny]

I'd be inclined to suspect mis measurement. My guess is that you didn't get the top off water stirred in thoroughly enough and got a watered down reading.

 

[Bobby_M]

Flavor impact? Just from the lower OG you're looking at perhaps a slight imbalance towards bitter since the FG will be lower (dryer finish).
Diastatic power = amount of enymes ready to do the starch to sugar conversion. It is measured per grain type but also think of it as a ratio within the whole grain bill. Base malts like 6 row have huge DP, 2-row slightly less. Highly kilned malts have progressively less as they get darker. Vienna and Munich are moderate where chocolate has none (destroyed by the heat).

When you have a very low overall DP in a grain bill, it CAN convert but it will take a long time and that time is temp dependent. In your case, maybe 90 minutes at 155F would have done it. Maybe 120 minutes at 148F. I'm pulling these number out of my ass for example purposes.

When you have a lot of base malt and very few kilned/adjunct grains, the overall DP is high and you can convert in 30-40 minutes.