Mash Efficiency

[callisbeers]

Last half dozen or so brews I have had a poor efficiency after mashing and sparking. I have had to add anywhere from a half pound of DME to today where I had to add 1.5 lbs. I haven't changed any procedures. The only thing I have done is starting buying my 2 row in bulk so it have been sitting in my garage for 2-3 months. I also am using a 10 gallon mash cooler compared to a 5 gallon. Any thoughts or suggestions?

 

[doug293cz]

Not enough information. How bad is your efficiency? Give us some numbers from one of your batches. Grain bill, water volumes, wort volumes, specific gravities? What is your process - fly sparge, batch sparge, no-sparge, BIAB?
What is your mill gap spacing set to? Have all the low efficiency batches been from a single lot of base grain?

Brew on

 

[callisbeers]

Last two batches:

Estimated SG = 1.062, reading pre boil, 1.040
Estimated SG = 1.049, reading pre boil, 1.030

Batch 1 (12 lbs grain) mashed with 4 gal, then sparged with 5.5 gallons, 7 gallons wort collected.

Batch 2 ( 10 lbs) mashed with 3.25 gal, then sparged with 5.75 gallons, 7 gallons wort collected

I have used both the mill at my local shop and my neighbors mill.

And yes all the low efficiencies have been from a single base grain. I have been storing the bag in the garage, someone said it may be the humidity. Has been warm and muggy this past month.

 

[kh54s10]

Did you use the same mill on any previous brew and gotten good numbers.

I would say that either your crush is not as good or that the grain has been compromised. Store cool and DRY. Get a bin with a seal on it. Store inside. I use 5 gallon buckets with Gamma Lids.

 

[doug293cz]

Last two batches:

Estimated SG = 1.062, reading pre boil, 1.040
Estimated SG = 1.049, reading pre boil, 1.030

Batch 1 (12 lbs grain) mashed with 4 gal, then sparged with 5.5 gallons, 7 gallons wort collected.

Batch 2 ( 10 lbs) mashed with 3.25 gal, then sparged with 5.75 gallons, 7 gallons wort collected

I have used both the mill at my local shop and my neighbors mill.

And yes all the low efficiencies have been from a single base grain. I have been storing the bag in the garage, someone said it may be the humidity. Has been warm and muggy this past month.

Your grain absorption + MLT undrainable volume is about 0.2 gal/lb which is considerably higher than the typical value of 0.12 gal/lb. That extra wort stuck in your MLT contains some of your sugar, so your efficiency is reduced.

I ran a batch sparge simulation using your numbers for the 12 lb grain bill (assumed weighted potential of 1.036.) If we assume that your actual grain absorption is 0.12 gal/lb, then in order to lose 2.5 gal in the MLT, your undrainable volume would have to be 1.06 gal, which is quite high. Then, assuming your sparging process was well conducted (good mixing), your conversion (saccharification) efficiency works out to 89% (percent of available starch converted to sugar.) This is not terrible efficiency, but it is possible for homebrewers to readily achieve conversion efficiencies better than 95%, and even 98% - 99% are attainable.

The low conversion efficiency could be due sub par (lower than normal extract potential) grain, either as received or because of poor storage conditions. It could also be due to too coarse a crush and/or too short mash times.

If I rerun the simulation after reducing your MLT undrainable volume to 0.125 gal, and adjusting the sparge water volume for equal pre-boil volume, The lauter efficiency increases from 75.8% to 84.9%, and mash efficiency (= conversion eff * lauter eff) increases from 67.4% to 75.6%, with a pre-boil SG of 1.045 vs. 1.040. 7 gal @ 1.045 boiled down to 5.5 gal would have an OG of 1.057, still below your target.

To get 5.5 gal @ 1.062 post-boil, you need 7 gal @ 1.0487 pre-boil. To achieve this with your "improved" MLT (0.125 gal dead volume), your conversion efficiency would have to improve to 97.5%. This all works out to an estimated mash efficiency of 82%, which might be overly optimistic.

So, you need to work on improving your conversion efficiency thru a combination of better grain storage conditions, longer mash times, and finer grain crush. You need to improve your lauter efficiency by reducing the undrainable volume of your MLT.

Brew on

 

[callisbeers]

Thanks for all the great advice! This is really helpful. To improve my lautering efficiency, is there something I should be doing that I am not. I will stir the mash once or twice and with about 40 minutes gone I will run-off about 3 pots full of wort to clear the bed. I generally heat about 20% of the sparge water to 200 add this to the mash quickly, meanwhile I have heated the remaining 80% to about 180 degrees. Once the 20% is sparged in, I slowly add the 80% over the next 60 minutes.

 

[doug293cz]

Thanks for all the great advice! This is really helpful. To improve my lautering efficiency, is there something I should be doing that I am not. I will stir the mash once or twice and with about 40 minutes gone I will run-off about 3 pots full of wort to clear the bed. I generally heat about 20% of the sparge water to 200 add this to the mash quickly, meanwhile I have heated the remaining 80% to about 180 degrees. Once the 20% is sparged in, I slowly add the 80% over the next 60 minutes.

Sounds like you are fly sparging. If so, that is much more difficult to analyze than batch sparging (I'm not aware of anyone who has published a mathematical model.) Also, the analysis I did above could be way off.

It would be very helpful if you could collect (or already have) SG measurements of the first wort run off after the mash is complete. Using this in combination with your grain bill and strike water volume, your conversion efficiency can be calculated. Then, knowing your conversion efficiency, and mash efficiency, we can calculate your lauter efficiency (since the batch sparge lauter simulation won't apply to fly sparge.) In order to isolate where in the process your poor efficiency originates (and therefore where it can be fixed) we need to have good numbers for both conversion efficiency and lauter efficiency.

Data that is not absolutely necessary, but could allow some sanity checking of other calculations is the SG of the last bit of wort collected at the end of run off.

Brew on

 

[callisbeers]

Sorry I wasn't clear on a couple of things (fly sparging). The readings I mentioned about are my wort recordings prior to boil.

Batch 1 = 1.040 x 7 = 280 / 12 = 23.3
Batch 2 = 1.030 x7 = 210 /10 = 21.0

Perhaps I am confusing my terminology but is this not First wort readings?

 

[doug293cz]

Sorry I wasn't clear on a couple of things (fly sparging). The readings I mentioned about are my wort recordings prior to boil.

Batch 1 = 1.040 x 7 = 280 / 12 = 23.3
Batch 2 = 1.030 x7 = 210 /10 = 21.0

Perhaps I am confusing my terminology but is this not First wort readings?

Those are your pre-boil SG's, and they contain the initial mash wort and sparged wort contributions to the total sugar. What is needed to calculate conversion efficiency is the SG of the wort in the mash, prior to adding any sparge water. The sample can be taken from the mash tun, vorlauf run-off (better from near the end of the vorlauf), or very first runnings out of the MLT (before there is any chance to mix with the sparge water.)

It is straight forward to calculate the maximum possible mash wort SG based on the grain bill and amount of strike water. Typical malt has an extract (sugar) potential of 80% by weight on a dry basis. Since the grain has about 4% moisture content, the actual extract potential on an "as-is" basis is 0.80 * 0.96 = 0.768 => 76.8%. So with 10 lbs of grain the maximum possible sugar (extract) @ 100% conversion is 7.68 lbs. Water weighs 8.33 lb/gal (@ 68˚F), so 3.25 gal of strike water weighs 3.25 * 8.33 = 27.07 lb. We can now calculate the maximum weight % sugar in the initial mash:

100 * 7.68 / (7.68 + 27.07) = 22.1% => 22.1˚Plato (since ˚Plato == Wt% sugar in the wort)
22.1˚ Plato converts to an SG of 1.0924 or 92.4 pts/gal​

We then calculate your conversion efficiency as:

1000 * (Mash_SG - 1) / 92.4​

The actual wort volume in the mash @ 100% conversion is then:

(7.68 lb + 27.07 lb) / (1.0924 * 8.33 lb/gal) = 3.82 gal​

80% dry wt potential is equivalent to 36.95 pts/lb potential, or an "as-is" potential of 0.96 * 36.95 = 35.47 pts/lb, so the total potential gravity points are:

10 lb * 35.47 pts/lb = 354.7 pts​

Your mash efficiency would then be:

30 pts/gal * 7 gal / 354.7 pts = 0.592 =>59.2%​

And your lauter efficiency can be calculated as:

100 * 59.2% / Conversion_Efficiency​

Once you know both your conversion efficiency and lauter efficiency, then you know which part(s) of your process is more in need of improvement.

Brew on