# Mash Efficiency Calculation

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#### Turbogator

##### Member
I recently brewed a batch of American amber ale and I went through the procedure to calculate the mash efficiency. But the number I came up with seems crazy high and I was hoping someone could check me and comment on the reliability of my calculation.

This is the resource I used to determine the calculation procedure. https://blog.eckraus.com/calculating-improving-mash-efficiency

The grain bill was 10 lbs. pale at 1.036 potential, 2.5 lbs. Vienna malt at 1.034 , 1.75 Crystal L60 at 1.036 and 1 lbs. of toasted malt at 1.033. I calculated the total points to be 541. These potential numbers all came out of beer smith.

I mashed it at 151 degrees for 60 minutes and sparged in two batches at 165 degrees. After the mash and sparge I collected 8.5 gallons of wort in my kettle

I calculated the total potential of the wort as ((541/8.5)/1000)+1 = 1.0636.

I measured the gravity of the wort I collected with both a hygrometer and a refractometer. The gravity was 1.050. Now 1.050 / 1.0636 =.9872 or 98.72 % is what the calculation calls for.

This seems crazy high. Am I doing this calculation wrong? Am I missing something?

Good morning, welcome to HBT!
I didn't check all of your numbers, but off the top of my head, 1.050 out of 1.064 is more like 80%
I think the problem is that the 1.000 is a constant, the weight of water. So you really only should be comparing the values after the decimal, .050/.0636. Try that and I think you'll find you're in range. But don't let it bother you either way. The important thing is that you'll make beer!

Sorry, you're dividing the wrong numbers. You need to divide the points, not SG gravities.
So your mash efficiency would actually come out to be 50/63.6 = 78.6%

Crush a bit finer perhaps? You should be able to get into the mid 80s for a 1.050-1.060 wort.
Do you stir well after the mash and each time you add sparge water?
Do you drain all the way?

Ok Now I see the error. Really 78% is good enough for me for now. If I want to dial it in at least I have a solid basis for doing so. I don't have any problem lautering so maybe a finer grind, or perhaps a slower lautering.
Thanks all.

The thing I've been scratching my head about is pre boil gravity . As I understand it you have to know what your OG is to calculate your prebg. So I assume the only way to know what your OG is gonna be you must know what your efficiency averages . I'm 75-80 and sometimes I'm higher then 80. So to be 100 % correct on a pre boil gravity you have to wait until you get post boil gravity . Unless I'm doing pre wrong . This is what I have for pre boil gravity .

Batch volume ×OG/pre boil volume =

If your historic brewing with similar grist gives you expected OG into fermenter using a recipe calculator set at some efficiency, then you can continue to use that efficiency percentage.
If your recipe calculator is dialed into your system for volumes, you can continue to use that.

If your calculator says you'll end up with 5 gallons into fermenter at 1.057, that's 5 * 57 points = 285
If you know you boil off 1 gal per hour and it's a 1 hr boil, then your preboil vol will be (5+1)=6 gal, and thus your preboil SG will be (285/6) = 47.5, or 1.0475.

There are nuances with vol losses due to kettle trub left behind, chiller deadspace if you've got that, etc.

Just remember not to use the "1.xxx" but the 1000*(SG - 1) values (eg, use 57 and not 1.057).

The thing I've been scratching my head about is pre boil gravity . As I understand it you have to know what your OG is to calculate your prebg. So I assume the only way to know what your OG is gonna be you must know what your efficiency averages . I'm 75-80 and sometimes I'm higher then 80. So to be 100 % correct on a pre boil gravity you have to wait until you get post boil gravity . Unless I'm doing pre wrong . This is what I have for pre boil gravity .

Batch volume ×OG/pre boil volume =
Your (post boil) OG is the target, but as long as you know your boil off rate, you can easily calculate what your preboil gravity should be. Within reason, boil off is a fairly constant rate, a volume per hour, on a given system, pretty much independent of the actual volume you're boiling. So a 4 gallon boil or an 8 gallon boil have similar boil off rate in the same kettle under same conditions, such as a gallon per hour.

You may actually boil off a bit faster with smaller volumes than larger ones due to being able to keep the wort temp higher, so adjust the heat accordingly so the surface motion is similar.

For starters I would estimate efficiency at 75-80% and boil off at 1 gallon/hr. Keep making adjustments to hone in on your system. It's much easier to add a little water toward the end (or leaving it at the slightly higher gravity) than boiling off an inadvertent extra half gallon, which may throw off your hop schedule.

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