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gravity during the mash/sparge

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bzwyatt

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I got a refractometer recently and I've started taking readings of my first runnings and the end of the mash. I usually mash/batch sparge in a rectangular cooler with a steel braid.

Yesterday I made a batch with 15 lbs of grain. My first runnings gravity was 1.074. Last runnings gravity was 1.034.

Seems like I'm leaving a lot of sugar in the mash tun, no? I mean that my gravity could be a lot lower than that by the time I'm done sparging.

Do you take gravity readings on the fly?

I have other related questions, so I hope to start a discussion, but if there are other threads about this, please link them.
 

Eucrid

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You can sparge down to around 1.010 before you get any ill effects like tannins.
 

Roundhouse

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I only take a gravity reading in the kettle as I'm (fly) sparging. Once you know your system efficiency and boil rate, you know what o.g. to shoot for in the kettle. I runoff until I hit this number. It may very well run below 1.010 but since my sparge ph never tops 6.0 or 170°, there is no concern of extracting tannins since you must meet both criteria. I could theoretically drain the grain down to 1.000 and not get them. I also sparge very very slowly to get as much of the sugars out as possible.
 
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bzwyatt

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A big part of what I want to figure out and/or adjust is getting the sugar. In theory, I can get it out, but I'd have like 10 gallons of wort to boil down to 5 gallons.

Is this just proof of the other elements of effiency? Like, if I had a better crush, my sparging gravity would drop quicker, so I'd still get ~7 gallons to boil to to ~5, but the OG would be 1.060 instead of 1.054 (for example)?

Or if I close my valve a little more, will the gravity go up, basically giving more time for the sugar to dissolve? And then my wort gravity would increase?
 

Roundhouse

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You need to think of mash efficiency as two separate things. You've got actual conversion efficiency which is the % of starches converted to sugars. This is affected by mash temperature, time and crush. The other is lauter efficiency which is how thoroughly you rinsed the converted sugars out of the grain. This is where the big differences between fly, batch, and no sparge come into play. Speed of lautering effects this as well. Slower being better. The conversion efficiency x the lauter efficiency equals the overall mash efficiency.

Let's say you hit a hypothetical 100% starch conversion efficiency. There isn't anything left to convert. That would be 100% (1.0) mash efficiency. However what if you only achieved 50% (.5) lauter efficiency? You only got half of those converted sugars into the kettle (1 x .5 = .5). Now let's say you had a batch where you only had 50% (.5) mash efficiency but had 100% (1.0) lauter efficiency. You still got 50% of the total sugar into the brew kettle (.5 x 1 = .5) but the quality of the worts compared to each other would be very different. You can see how different aspects of a mash can result in different products.
 

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A big part of what I want to figure out and/or adjust is getting the sugar. In theory, I can get it out, but I'd have like 10 gallons of wort to boil down to 5 gallons.

Correct. If you want to maximize efficiency, you'd want to sparge more. However, most home brewers are happy to sparge up to their boil volume, taking a bit of a hit in efficiency for expediency and of course fuel savings as well.

Those one reason many of us have lower efficiency % numbers with big grainbills. We reach our boil volume long before the maximum amount of sparging volume is reached.
 

Bobby_M

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A big part of what I want to figure out and/or adjust is getting the sugar. In theory, I can get it out, but I'd have like 10 gallons of wort to boil down to 5 gallons.

Is this just proof of the other elements of effiency? Like, if I had a better crush, my sparging gravity would drop quicker, so I'd still get ~7 gallons to boil to to ~5, but the OG would be 1.060 instead of 1.054 (for example)?

Or if I close my valve a little more, will the gravity go up, basically giving more time for the sugar to dissolve? And then my wort gravity would increase?
Nope. In batch sparging there are really no aspects of fluid mechanics involved in efficiency. The only way to ensure highest efficiency (assuming you drain, sparge, drain) is to reduce deadspace the best you can or otherwise ensure a complete first runoff. Propping up the far end of the cooler on a piece of 4x4 scrap would help quite a bit.

Batch sparging is a game of dilution. After each runoff, the remaining sugar in the tun is runoff gravity * (grain weight *.1) . So, 1.074 * 15 pounds *.1 means that there was at least 1.5 gallons of 1.074 wort left just in grain absorption alone (that's a total of . If you didn't get all of your strike water (minus 1.5 gallons of absorption) out, that would be called additional dead space.
 

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