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I just put my second AG batch into the primary, but I ran into an issue I need some help with.

When I did my first AG batch, I used water that was treated by a water softener (I know, I know...it was all I had at the time). My calculated efficiency came in at 75%, using grain points and pre-boil gravity formula. BeerSmith confirmed reading.

For my second batch I used a combination of water from a rural mountain property well and chlorinated city water. (I plan to profile PH, etc. at a later time)

After mash @ 153F and batch sparge @168F, I only had about 5 gallons of runnings...I think due to the difference in water profiles. I'm thinking the lack of minerals in the soft water for my first batch prevented the grain from hanging onto it...that's a different question.

To compensate for the additional 1.5 gallons of water I needed to reach 6.5 gallons, I ran more water back through my mash tun, over the grain until I had reached 6.5 pre-boil. I stirred the wort vigorously and took a gravity measurement, which came in at around 1.022.

Using the same efficiency formula used for my first batch, I show my mash efficiency for this batch super low at ~ 49%. I double checked in BeerSmith which reports ~ 47%.

Is it possible that the topping off of the additional 1.5 gallons diluted the water, giving me a false gravity reading, or is this more likely a water issue?

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The water profile is ulikely to affect how much wort you get out of your mash tun. Grain absorbs the same amount if water regardless of the mineral content. –  Tobias Patton Feb 26 '12 at 15:33
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1 Answer

up vote 1 down vote accepted

I don't think grain absorption varies according to mineral content, so that's not the cause of the problem.

For the top up runnings, I would have done that as a 2nd batch sparge - add the extra 1.5 gallons, stir vigorously and leave for 30 mins. Simply running the liquor over the grains won't pick up much sugars unless you let it trickle slowly out over a 30 minute period, and that you have a manifold that reduces channeling. The usual batch sparge setup of a bazooka screen isn't well suited to continuous sparging, but very well suited to batch sparging.

While temperature plays a key role in conversion performance, so does pH. The different water profile could have resulted in a high or low pH compared to your previous batch. This could have affected conversion rate - conversion may not have fully completed when you took the first runnings. Next time, check your mash pH, and add food grade lactic or phosphoric acid if it is too high, or add baking soda if it is too low - target is 5.1-5.5 pH - and all else being equal, a lower pH gives a slightly drier beer. For the acids, use 1ml at a time - for the baking soda, use 0.5tsp at a time.

I'm assuming the crush was the same, but check that also since it can affect extraction efficiency.

Did you use different amounts of mash/sparge liquor according to the predicted absorption of the grain? I'm guessing the amount of grain for the 2 batches was different, and so the amount of liquor will also need to be different.

All in all, my bet is on the different pH of the water affecting the mash, not the absorption rate.

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Crush was the same and there were different amounts of water between batches. I did realize after posting this that I didn't account for temperature when taking my gravity reading. My wort was likely around 110 - 120 F when I took the reading. –  Matthew Feb 26 '12 at 17:00
    
Ok, then correcting for temperature, assuming 65-68F calibration gives a reading of 1.032. If 1.022 == 47%, then 1.032 = (32/22)*47 = 68%. Which is more in line with your previous batch. pH can certainly affect conversion efficiency by 5-10%. So, the less effective final sparge and the pH is probably where your lower extract comes from. –  mdma Feb 26 '12 at 17:10
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