Why the jump in mash efficiency?

**SOLVED**
See thread for details.

I brewed an oatmeal stout last weekend. It's my third all grain brew and my first two landed an efficiency of about 68%. Since this is my first 20+ SRM beer, I did some reading that the darker crystal grains can lower the mash pH below 5.5 target. I got my water analysis and used several online calculators to determine that I needed to up my residual alkalinity to achieve a 5.5 pH. I ended up adding 5g of baking soda and 1g of gypsum to the strike water. After mixing the grains with the water and stirring for several minutes, I used a pH strip and it read 5.8. I tested again following the 60 minute mash and it again read 5.8. I assumed that I added too much baking soda, which led to the higher mash pH. However, when I took my pre-boil gravity, I was at 79% efficiency (a jump of 10%). I had to boil a gallon of water and add it into the boil to get closer to my estimated pre-boil gravity.

I'm racking my brain here to figure out why I had this jump in efficiency. I did everything exactly as I'd done my previous brews with the exception of the following:

1. Added baking soda (5g).
2. Used a fine mesh strainer when transferring to the kettle so I can completely drain the MT into the kettle. In the past, I've stopped right before the end because I usually get a lot of grain/husk material at the end.
3. My sparge water temp was 168 (mash temp was 156), so there was no mash out. In the past, I used 180F sparge water to achieve a 170F mash out.

My only thinking is that somehow the test strips were off (40 SRM wort might affect the color?), and adding in the baking soda corrected a mash pH issue I didn't know I had. Or perhaps the 15 minute rest with the lower sparge water temp allowed for more extraction? I'd really like to figure out a game plan for my next brew. Any ideas?

This is a bit off topic but I've never added more than a gram of baking soda for adjusting my water. Were you only adding these to adjust your PH? Personally, I never had any luck messing with my water chemistry till I got an updated water report and updated the water profile for Milwaukee in beersmith. If you weren't adjusting with a target profile in mind your beer might taste funny.

Oh and to answer your question with another possibility, perhaps by not mashing out you allowed the grains to finish converting the starches while they drained. Whereas on your previous batches you halted enzymatic activity by mashing out. Perhaps you just need to mash longer to get better efficiency more consistently.

If you didn't crush your own grains the quality of the crush may have changed and that can greatly affect your efficiency.

PH strips are not meant to measure at mash temperatures. I assume you cooled your sample to room temperature and I've read that the difference between mash temps and cool temps is around .3. If this is accurate then you stumbled upon a 5.5 pH. Besides, Bru'nWater shows the acceptable mash pH as 5.2 to 5.8 when measured at room temperatures.

same exact thing happened to me with my oatmeal stout a few weeks ago. went from 65% efficiency to 84%. i also mashed for 90 mins instead of 60 mins which i think was the culprit for me.

mkravitz13 said:

same exact thing happened to me with my oatmeal stout a few weeks ago. went from 65% efficiency to 84%. i also mashed for 90 mins instead of 60 mins which i think was the culprit for me.

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I wouldn't call it a culprit as much as I would say you should've been mashing longer the whole time

If you've stopped draining before the end before, you've been leaving some of your sugar in the mash tun, so I'd definitely that that's a leading possibility.

Thanks everyone for their response.

dawgmatic said:

Were you only adding these to adjust your PH?

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Yes, it was purely to add more pH buffering with what I had on hand.

dawgmatic said:

Perhaps you just need to mash longer to get better efficiency more consistently.

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Nice observation. I'll try that next time and see what happens

RM-MN said:

If you didn't crush your own grains the quality of the crush may have changed and that can greatly affect your efficiency.

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I thought of this as well. However I got my grains crushed by the same LHBS and I don't think they've adjusted their mill.

cluckk said:

PH strips are not meant to measure at mash temperatures. I assume you cooled your sample to room temperature and I've read that the difference between mash temps and cool temps is around .3. If this is accurate then you stumbled upon a 5.5 pH. Besides, Bru'nWater shows the acceptable mash pH as 5.2 to 5.8 when measured at room temperatures.

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I've read the same as well. I read that the strips typically read .3 lower where in my case it seemed to be .3 higher. I did cool the samples to room temperature before taking a sample. Perhaps these particular strips (from my LHBS) are +-.2 or +- .3, which might explain things.

latium said:

If you've stopped draining before the end before, you've been leaving some of your sugar in the mash tun, so I'd definitely that that's a leading possibility.

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Makes sense. I usually stop draining when I start to see a sudden rush of grain/husk material. Since I had a strainer, I just let it all come on out this time.

What do others do? Do any of you have the same issue with the rush of stuff at the end of the draining?

Vertigo00oo said:

I've read the same as well. I read that the strips typically read .3 lower where in my case it seemed to be .3 higher. I did cool the samples to room temperature before taking a sample. Perhaps these particular strips (from my LHBS) are +-.2 or +- .3, which might explain things.

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I wasn't sure about up or down for the strips. I use a pH meter with automatic temperature compensation.

cluckk said:

I wasn't sure about up or down for the strips. I use a pH meter with automatic temperature compensation.

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Which meter do you have?

I have this one: http://www.amazon.com/dp/B004G8PWAU/?tag=skimlinks_replacement-20

If you get it you also need the calibration and storage solutions.

So on my batch this past weekend, I did everything I normally do except I fully drained the mash tun instead of stopping when it starts gurgling.

No change in efficiency. Still at 68%.

Next batch I'm going to mash for 90 minutes and see where that puts me.

Brewed a Belgian Dubbel yesterday and as noted earlier, performed a 90 minute mash. I then sparged with 180F water for about 15, mixed everything up real well, and got the 78% efficiency I got batch before last!

So, in my case, it seems as though the batch before last when I saw the jump, I sparged with a lower temperature water, which prolonged the conversion process and led to more extraction. Next time I brew, I'm going to perform another 90 minute mash to see if I got the same efficiency.

The confusing part to me, is that I've read that the conversion process should only take 45 minutes or so, which is why most people mash for 60. I wonder why in my case it's taking longer? If I can get consistent with my 90 minute mash, I'll drop it to 75, because I doubt the last 15 minutes of the 90 is really doing anything. This kinds of makes me wonder if I should check the calibration on my thermometer.

Conversion takes less than 10 minutes. The rest of the time is used to get the grains wet to the center of the particles and the sugars leached back out. Post a picture of the grain you used so we can see the quality of the crush. I'd bet that you would do better with a finer crush.