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?