Help with mash efficiency

[aric6785]

I really didn’t want this to be my first post... but I need help from the gurus... This is my second all grain brew using the mash and boil... Did I mess up somewhere? 13lb grain bill. It was a recipe kit... Pre boil SG after cooling the sample to 75 was 1.070... Here’s the recipe.

7.0 Rahr 2 row
4.5lbs White Wheat Malt
.75lbs Unmalted wheat
.75lbs Flakes oats

I used 4 gallons of strike water at 163 degrees with a saach rest at 150 for an hour and then brought it up to 170 for mash for 10 minutes... I then sparge with approx 5 gallons at 175 and had a pre boil of just under 7 gallons... Here’s the recipe on paper. Any help for a newb?
OG is spot on at 1.065

Btw... Love the board and all the help I’ve been able to research!

 

[magno]

You ask if you messed up somewhere, but your OG is spot on... What was/is the problem? Seems like everything worked out to me.

 

[aric6785]

Yeah, I posted during the boil, prior to the OG reading, then went back and edited with the OG reading. I think I’m good, but we’ll see! I’m still just trying to get the hang of calculating Mash Efficiency.

 

[McKnuckle]

Your pre-boil gravity cannot be higher than your OG, so one of them is wrong.

Usually it’s the pre-boil value. It is very easy to get that wrong, because wort can stratify, with the heavier sugars sinking and the upper layer being more dilute. If you don’t stir thoroughly you may get a sample that’s not representative of the aggregate.

With a bit under 7 gallons going into the boil, and 5 gallons exiting, your pre-boil would have been around 1.047.

https://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/

This being said, did you use a hydrometer or a refractometer? A hydro is more forgiving.

 

[aric6785]

I used a hydrometer... I also stirred it pretty good. That’s why I’m confused by the reading I got.

 

[Qhrumphf]

If your preboil was 1.070 and post boil 1.065, then at least one of those readings is wrong.

The only way to decrease the gravity (apart from fermentation) is to dilute it. If you concentrated the wort via a boil, it's physically impossible for the gravity to decrease.

What likely happened is your pre-boil reading wasn't mixed well (very common problem including at the pro level) and you grabbed a sample that was more first wort than last wort (ie it wasn't a representative sample and looked higher gravity than it actually was).

Odds are your post-boil OG reading was correct, so ultimately shouldn't be an issue. Pre-boil matters only if you need to be able to correct it (more water, more fermentables, adjusted boil time, whatever the case may be).

Stir well, recirc, or whirlpool (or something) before taking a preboil reading to get a good consistent reading. I took to just letting it boil for 30 seconds or so before grabbing a reading when stirring it wasn't an option.

 

[aric6785]

I got the sample from the spigot... I’m guessing I probably should’ve gave it a good stir before opening the ball valve. I got the mash and boil with the recirc pump... I’ll try stirring it and then right after the boil starts, get the sample.

 

[Qhrumphf]

If you pulled from the bottom, that'd certainly explain a higher than representative reading.

If you let it sit long enough it'd eventually diffuse together (though how long I don't know).

Running off into your kettle at an angle such that it creates constant rotation will also help do a lot of the work for you by mixing throughout.