Missed O.G. on partial mash by 5 points using sous vide - any thoughts?

[J2W2]

Hi,

I just brewed a partial mash British Brown Ale for the second time and I missed my target O.G. by 5 points - 1.049 vs 1.054 (I'm getting the target gravity from BeerSmith).

The first time I brewed it was almost two years ago, and I was using a 2-gallon beverage cooler as a mini mash tun at that time. That brew hit the O.G. exactly. The grain bill for the partial mash is 4.3 pounds, and I used six quarts of water, which pretty much completely filled the 2-gallon cooler. After mashing for an hour, I drained it into my kettle and rinsed the grains with a gallon of 168 degree water.

I could never hold my mash temperature in the cooler, so I switched to a sous vide about a year and a half ago. Today I used the same recipe. I bagged the grains and put them in six quarts of water with the sous vide at 154 degrees for an hour. When the mash was complete, I dunked the bagged grains several times in my kettle water, which was heated to 170 degrees, and let them drain over the kettle. I then followed the same process as before.

Does anyone have any thoughts on the gravity difference? I would think mashing at the proper temperature would be more efficient if anything. Perhaps rinsing bagged grains in the kettle is not as efficient as rinsing loose grain in a mini mash tun?

Thanks for your help!

 

[J2W2]

I just checked on another partial mash I brewed since switching to the sous vide. That was a German Alt Beer with a grain bill of 2.4 pounds. The sous vide version was one gravity point lower than the mash tun version. So now I'm more confused since that one was so close. Unless dunking the smaller grain bill in the kettle did a better job of extracting the sugars than dunking the larger one?

 

[MikeCo]

Was the grain crushed more coarsely than before? Another reason could be less boil-off than assumed.

 

[doug293cz]

From your description, I assume you are dunking the bag in the wort that it just came out of. Is this correct? If so, this does nothing to extract additional sugar from the grain mass (it's equivalent to trying to rinse soap off of dishes by dipping them back into the soapy water.) To rinse additional sugar from the grain mass, you have to rinse (sparge) with fresh water (doesn't matter if it's hot or cold.)

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