Today’s brew day marked my first as an all-grain brewer – thanks to all of you who chimed in to my previous posts and queries as I worked up to this batch. Truth be told, I actually started heating my strike water at 6:45am, due to the fact that our 4-month-old decided to wake us up at 5:30. On the upside, I was all cleaned up by 11:30.
In keeping with the advice I was given, I tried to take good notes along the way, which resulted in the following:
Recipe: Town Hall Hope & King Scotch Ale
Mashed in with 3.75 gallons of water heated to 164 degrees
Rested at 151 for 1 hour (only lost 1 degree over the hour!)
Mashed out with 1.25 gallons of boiling water, bringing the mash to 160
Collected 3.5 gallons of first runnings
Sparged with 3.5 gallons of water heated to 171, bringing the mash to 163
Collected 3.5 gallons of second runnings for a total of 7 gallons (per target)
The boil went as expected
Pre-boil gravity was 1.040
Post-boil gravity was 1.050 (target was 1.060)
I am hoping these numbers might give more knowledgable heads than mine a way to answer the following:
How do I calculate my efficiency?
Why was my post-boil gravity 10 points low?
What will coming in 10 points under do to the beer? (I’m guessing it will still be drinkable)
I use the program beersmith to help me with my brewing needs, that said when you type in your recipe it gives you a target OG at 75% efficiency. one reason your OG could be low is if you did not crush the grains yourself. when i ordered pre crushed grain i never hit my og ever. now that i have a maltmill i get about 80% efficiency batch sparge method. coming in ten points under will be a less alcoholic beer, maybe even a bit thinner as well. Not as much sugars to convert, also if you used alot of hops they may be more potent. if you have DME or liquid extract you can always add to get the right OG when if your mash was a bit off.
Post boil volume was just under 6 gallons, so I lost a little over a gallon during the boil. I was expecting to put 5.5 into primary, but overshot that by a bit…
[quote=“speed”][quote=“Glug Master”]Having nearly a gallon more post boil is why your OG Is low.
Run your numbers through this calculator at Beerheads.com Brewheads.com - <?=$pagetitle?>
to see what your efficiency was.[/quote]
that takes me to bargain fittings :? [/quote]
[quote=“Dan S”]total of 7 gallons (per target)
Pre-boil gravity was 1.040
Post-boil gravity was 1.050[/quote]
FWIW, at least one of those four numbers is wrong. If you had 7.0 gal at 1.040 pre-boil, then to be at 1.050 post-boil you would have to have 5.6 gal. If you had 5.9 gal, the OG would be 1.047.
So for starters I’d calibrate your hydrometer/refractometer and whatever you use to measure volumes. Also, when you pull a sample of hot wort to check gravity, make sure it’s cooled to room temperature, and that it’s covered while cooling.
Efficiency calculation is pretty simple. Basically, you just divide the total sugar extracted from the grist by the total starch present in the grist to begin with. To be exact, you’d need to look up the potential extract for each grain and do a weighted average, but you can get close by just assuming an overall value of ~36 point-gal/lb.
Since you have ~12 lb of grain, the total potential extract is (12 lb)*(36 point-gal/lb) = 432 point-gal
Assuming your readings of 1.040 at 7.0 gal are correct, the actual extract is (40 points)*(7.0 gal) = 280 point-gal
So your efficiency was 280/432 = 0.648, or 65%. NB’s kits assume 70%, so if you’d boiled down to 5.0 gal you would actually have been pretty close (1.056).
Thanks to everyone for the feedback – a10t2, thanks especially for taking the time to tinker with the numbers in detail. I’m pretty sure that my hydrometer is taking accurate readings (and I did cool the pre-boil wort before taking the reading), but will double check with plain water just to be sure. If anything, my means of measuring volume is probably the culprit, given that I simply used a measuring plastic stick marked with 1/2 gallon increments. While I did measure the water when making it, I’m sure I could have been more careful with the process.
Also, I was expecting to lose 1.5 gallons during the boil (per a calculator I found somewhere that determined boil off by the diameter of the brew pot), but did not lose that much. Would it be fair to say that I should consider adjusting the pre-boil volume from 7 to 6 gallons for the next batch so that I boil down to 5 gallons going into primary?
That’s what I would do. I lose around a gallon during the boil and cool down. If you want to finish with 5.5 gallon you will need to adjust your recipe for the extra half gallon, that’s where a program like Beersmith comes in handy.
[quote=“Dan S”]
Also, I was expecting to lose 1.5 gallons during the boil (per a calculator I found somewhere that determined boil off by the diameter of the brew pot), but did not lose that much. Would it be fair to say that I should consider adjusting the pre-boil volume from 7 to 6 gallons for the next batch so that I boil down to 5 gallons going into primary?[/quote]
Sounds about right. I usually have no problem boiling down 7 gallons to 5.5 on a high output banjo burner on a calm day, preferring as vigorous a boil as my pot can manage. If that’s not an option, dialing back your pre-boil volume is the way to go.
