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I love doing all-grain, but man, it's giving me a headache lately. I've done 7 now - 4 have turned out fine, 1 started out fine, but I messed up the fermentation, and the remaining 2 have had starting gravities all over the place.

I did a 2.5 gal batch of a blonde ale about a month ago. The target OG for the fermenter was 1.050 and somehow I managed 1.055. Any time I've missed in the past, it was always a tad on the low side, so I'm certainly wondering what happened this particular time to get much better efficiency than I normally see.

Last week I brewed up 5 gal of an IPA. The target OG for the fermenter was 1.065, but I only managed 1.050. That's a pretty significant miss in my mind, and I don't think I did anything differently from what I've done before.

What sorts of things could cause these wild swings?

Typically with a higher gravity batch you'll get lower mash efficiency so that would support your lower efficency with the IPA. This is mostly to do with mash thickness, how large your tun is and if you can get the same thickness as you normally do, etc.

Another thing is that with your smaller 2.5 gallon batch and variance in your boil off / target volume will have a larger effect on your original gravity.

In addition, some of this could be explained by your system and process. BIAB? Does the bag fill the pot? Dead space? Do you stirr your mash?

RubberToe wrote:Typically with a higher gravity batch you'll get lower mash efficiency so that would support your lower efficency with the IPA. This is mostly to do with mash thickness, how large your tun is and if you can get the same thickness as you normally do, etc.

Another thing is that with your smaller 2.5 gallon batch and variance in your boil off / target volume will have a larger effect on your original gravity.

Mash thickness? As it how thick or thin/runny/watery the grain/water mix is? In this particular case, it was a little thicker than usual.

RubberToe wrote:In addition, some of this could be explained by your system and process. BIAB? Does the bag fill the pot? Dead space? Do you stirr your mash?

I don't do BIAB. I do stir my mash 2 or 3 times over the course of the rest (60 mins).

Buccaneer wrote:

RubberToe wrote:Typically with a higher gravity batch you'll get lower mash efficiency so that would support your lower efficency with the IPA. This is mostly to do with mash thickness, how large your tun is and if you can get the same thickness as you normally do, etc.

Another thing is that with your smaller 2.5 gallon batch and variance in your boil off / target volume will have a larger effect on your original gravity.

Mash thickness? As it how thick or thin/runny/watery the grain/water mix is? In this particular case, it was a little thicker than usual.

RubberToe wrote:In addition, some of this could be explained by your system and process. BIAB? Does the bag fill the pot? Dead space? Do you stirr your mash?

I don't do BIAB. I do stir my mash 2 or 3 times over the course of the rest (60 mins).

Not sure if this is exactly what you are asking for but I found this link to be really helpful in understanding how mash efficiency works. And how to make it stable.

http://www.braukaiser.com/wiki/index.ph ... on_mashing" onclick="window.open(this.href);return false;

basically the thicker your mash is, the more grain there is and the more sugar there is as well. So it takes more water to wash away the same percentage of sugars that would be washed away from a thinner mash. Said another way, your efficiency goes down because you didn't rinse the grain as well. There are some other differences but that is the main one.

I had this issue when I first started all-grain and it turned out that I was checking gravity at too high of a temperature leading to low OG readings. Make sure you check your gravity at standard temp or apply a correction.

I have made the mistake of taking a sample from the top or bottom of unstirred runnings which led to gravity readings that were way off (I find that the later, lighter runnings mostly just sit on top with my system). Make sure to give the runnings a good stir, and apply a temperature correction as Joe suggested. Apart from this and the thickness of the mash as others have said I can't think of anything that would swing your efficiency so heavily.

Excellent information, guys. I already do my measurements keeping temperature in mind - that burned me once before.

I always measure after I do the sparge - I give the kettle a stir and take the sample. It's entirely possible I didn't stir enough.

The mash was definitely thicker this time around. I know the rule of thumb is typically 2 quarts of water per pound of grain (or 4L per kg). I'm not religious about it, though - I usually add two 10L jugs of water for the mash (and the jugs are usually full to the top, so it's probably more like 11 or 12L). Keeping temperature up seems to be a problem for me, so I always end up adding a couple tea kettles full of water as I go. It was warmer this time around, so I didn't need to add much water after. And it seemed that there was less in there right from the start.

Normally I lauter about 3 to 3.5 gallons, then batch sparge to make up the rest. This time, however, I only got 2 gallons. Knowing now that a thinner mash is better, I shall be keeping a close eye on this in the future.

You mention that you check your gravity after the sparge - how was your measured pre-boil gravity compared to your target pre-boil gravity?

One thing that wasn't mentioned, is it possible that in addition to a lower efficiency due to the higher target OG, you had a measurement error when weighing in your grain? I've had that happen before, and ended up turning my APA into an IPA on the fly once it was discovered on my pre-boil readings.

LeafMan66_67 wrote:You mention that you check your gravity after the sparge - how was your measured pre-boil gravity compared to your target pre-boil gravity?

One thing that wasn't mentioned, is it possible that in addition to a lower efficiency due to the higher target OG, you had a measurement error when weighing in your grain? I've had that happen before, and ended up turning my APA into an IPA on the fly once it was discovered on my pre-boil readings.

Unfortunately, I don't know what the pre-boil gravity was supposed to be. From the recipe data that I have, though - Boil Size: 7.07 gal Boil Time: 60 min End of Boil Volume 5.72 gal. I was just slightly over the 7 gal pre-boil and was 5.25 end of boil.

As for the weight of the grain, I can only assume that Dave measured it out correctly for me.

Anyway, I have lots of stuff to pay attention to next time around and hopefully this was just an anomaly.

I used to have similar problems. The main issue was boil off and volume measurement error (both of which resulted from a poorly calibrated sight gauge). Given the differences in gravity between your two batch sizes, I'd suggest that boil off might be your primary issue. You should run a couple of a tests with just water in the pot to figure out what your per hour boil off volume is (note: not percent, but actual volume), if you haven't already. And double check that whatever you use to calculate volumes is correct. (I had my sight gauge markings wrong because I calibrated using one of the 5000 ml Erlenmeyers that we got through a group order. When I checked the volume indications on the 5000 ml by weight, however, after a series of frustratingly swinging mashes, it was substantially off. As a result, all of my volumes, from boil off the strike volume, etc., had been off as well, along with my efficiency calculations, since I used the flask to calibrate my sight gauge.)

Ah. I just read the thread closer:

"Unfortunately, I don't know what the pre-boil gravity was supposed to be. From the recipe data that I have, though - Boil Size: 7.07 gal Boil Time: 60 min End of Boil Volume 5.72 gal. I was just slightly over the 7 gal pre-boil and was 5.25 end of boil."

And:

"Last week I brewed up 5 gal of an IPA. The target OG for the fermenter was 1.065, but I only managed 1.050."

Your boil off is higher than the factor in the recipe, so you do need to check it and adjust water volumes accordingly, but that actually makes your efficiency even worse. Assuming that you accurately measured gravity and final volume, you actually got an OG of 1.046 (adjusted to 5.72 gallons), rather than the 1.065 you were aiming for.

I'd still suspect that it is a measurement issue (gravity or volume), but if not, check the link above about efficiency.

Just one other thought - you are measuring in US gallons?

I'm measuring in US gallons.

I like the idea of testing my boil off rates. When I go back and look at what I've recorded in past brews, the boil off on my last batch was way higher than usual. As you said, though, a normal boil off would have made things worse.

I think I'm also going to pick up a second hydrometer.

A refractometer would probably be a better investment. Let's you easily take readings during the lautering/sparge process.

jeffsmith wrote:A refractometer would probably be a better investment. Let's you easily take readings during the lautering/sparge process.

Yeah! I bought mine from a reseller on Amazon. It really helps on brewday.

One of my best investments

It's been on my wishlist for a while. Guess I'm gonna pull the trigger.

Any suggestions as to which one I should get? I was thinking this one http://www.amazon.ca/gp/product/B000FBL2G0" onclick="window.open(this.href);return false; or this http://www.amazon.ca/Happy-Hours-Beer-R ... B00WGA8NO2" onclick="window.open(this.href);return false;. Same price, with the first being on sale and doing only Brix only and the second doing Brix and SG.

Buccaneer wrote:Any suggestions as to which one I should get? I was thinking this one http://www.amazon.ca/gp/product/B000FBL2G0" onclick="window.open(this.href);return false; or this http://www.amazon.ca/Happy-Hours-Beer-R ... B00WGA8NO2" onclick="window.open(this.href);return false;. Same price, with the first being on sale and doing only Brix only and the second doing Brix and SG.

The SG scale on these is not accurate (especially at higher gravities). So it really doesn't matter much. I recently switched over to a digital one, and find it alot easier to use.

AllanMar wrote:I recently switched over to a digital one, and find it alot easier to use.

Source?

jeffsmith wrote:

AllanMar wrote:I recently switched over to a digital one, and find it alot easier to use.

Source?

http://www.amazon.ca/Milwaukee-Instrume ... ords=ma871" onclick="window.open(this.href);return false;

Goes on sale from time to time. Think I paid $109ish?

AllanMar wrote:

jeffsmith wrote:

AllanMar wrote:I recently switched over to a digital one, and find it alot easier to use.

Source?

http://www.amazon.ca/Milwaukee-Instrume ... ords=ma871" onclick="window.open(this.href);return false;

Goes on sale from time to time. Think I paid $109ish?

Thanks!