Efficiency confusion

[wlssox524]

Hi all,

I brewed up a blonde ale this morning and am having some confusion around efficiency. I took a preboil sample after mixing the kettle thoroughly and hit 1.29 with 7.4 gallons. Grain bill was 7# two row, .75# carapils, .5# crystal 10, .5# Vienna Not great but chalked it up to a bad crush as I usually hit low to mid 70s for efficiency.

The trouble started when I took the post boil measurement--I read 1.030 with 5.5 gallons. I have no idea how this happened but I seem to have lost 50 gravity points. My volume measurements may be slightly off but I'm using a sight gauge so I don't think they are wildly so. I used two different hydrometer for the post boil measurement because I thought that might be the issue but they read the same. I measured the post boil gravity once using wort poured from the spigot and once in the fermenter. Same result both times

Any ideas what might have happened? I poured everything from the kettle into the fermenter so I don't think that's the problem. Something seems to have happened in the boil. All hydrometer readings were near 60f and temperature corrected. I used a paint strainer for my hops and I squeezed it out before removing. No idea if that could be a factor

Any ideas??

 

[acidrain]

Was the wort temp down to 68F (or whatever your hydrometer is calibrated to)?

 

[stpug]

64% efficiency on preboil of 1.029 SG @ 7.4 gal
FG should be 1.039 @ 5.5 Gal, assuming all of the BK went into fermenter and you are accurate on volume of fermenter

I'm not sure where you get the 50 gravity point loss. I calculate about 10 gravity point difference based on volumes and preboil gravity. Fifty gravity points would be the difference of 1.010 and 1.060.

Did the crush look not so good? If it looked fine then trust the preboil gravity and confirm what your final volume in the fermenter was 5.5 gallons. If it was 5.5 gallons, then go off of your preboil gravity and calculate down to your volume (i.e. 1.039).

I don't know what has happened or why you are seeing the readings that you are, but I do know that many other folks have run into the same scenario (i.e. a couple point difference from preboil to OG). There are many factors that can affect your readings and it's just a matter of figuring out your system so that you can collect accurate gravity readings. I personally use a refractometer for ALL readings (preboil, OG, FG). I have performed parallel readings on FG with both my refractometer and hydrometer, and am personally finding a 0.5-1.5 point discrepancy (i.e. minimal to negligible). For the ease of using my refract, it's acceptable. However, I'll keep performing these dual-readings to ensure that I can fully trust my refract for FG readings with correction.

Anyway, back to your situation.... Like I said, I would trust the gravity readings that you feel most comfortable with. Judging your lautering, crush, volumes, etc, which gravity reading felt the most accurate to you? I suspect your preboil was more accurate because that would put you in the high 60s efficiency (preboil gravity) versus around 50% efficiency (postboil gravity).

What do you think?

 

[wlssox524]

Here's what I mean by losing 50 points:
-I measured 1.029 (at 70 degrees) with 7.4 gallons=29*7.4=214.6 total gravity points

Based on that I would expect the same wort boiled down to 5.5 gallons to come in at 1.039 (at 70 degrees) (=214.6/5.5)

And yet my cooled, post-boil measurement came in at 1.030. Obviously one of these measurements has to be wrong since I started with 7.4 gallons of 1.029 wort and poured all the boiled down contents into the fermenter.

So ultimately, one of 2 things happened
1) I lost a ton of sugar from the beginning of the boil to the fermenter. Not sure how this would have happened since I poured all the boiled down wort into the fermenter. The only thing I can think of is that I took out the hops before pouring to the fermenter (1 oz of leaf hops in a paint strainer which i squeezed out)
2) My pre-boil or post-boil measurement is wrong. I'm totally baffled..I've never had efficiency issues so I would be shocked if my pre-boil number was actually below 1.029, but I measured the post-boil gravity with 2 separate hydrometers and both read 1.030.

 

[stpug]

AFAIK, you can't lose sugar during a normal boil. You'll only lose water thereby increasing the gravity of your wort. I think it's impossible to lose sugar during a standard boil.

I also suspect an incorrect reading somewhere along the way. I suspect your preboil to be correct based on efficiency percentages, but it's possible you left behind some sugar in the MLT leading to the extreme low efficiency. Unfortunately, once you're fermenting it'll be hard to backtrack your OG. HOWEVER, you can approximate your OG using a hydrometer reading the refractometer reading once you reach FG. Woodlandbrew has a formula somewhere that I've used once and it is very reasonably close to what I had approximated (a few points difference). It's not perfect but it should give a reasonable value which should be close to one of your OG figures. If I can find it, I'll post the link.

 

[stpug]

Here it is:
OG = -1.728(FG_HydrometerGravity) + 0.01085(FG_RefractometerBrix) + 2.728

Here's where it comes from:
http://woodlandbrew.blogspot.com/2013/02/abv-without-og.html

It's not perfect but it should get you close to the OG, at which point you can compare with the possible OG values and decide which is most likely the correct OG.

 

[feinbera]

Can't be the hops; you're missing almost a quarter of your sugars, and 1 oz of hops aren't gonna absorb a quarter of your wort, even if you don't squeeze 'em out.

I suspect your pre-boil reading was off, since you took two post-boil readings and they agreed. Did you also note gravity and volumes of first runnings, first sparge, and any subsequent sparges? Those numbers should provide a "sanity check" on the overall pre-boil numbers, if you made note of them.

Unless... did you have a ginormous boil-over and lose a quarter of your wort at some point?