What am I doing wrong? - Gravity calculations

[IanWatson]

I've started to make my own recipes. I typically do 5 gal BIAB partial mash/steeping. I've been calculating the expected gravity per the methods of "Designing Great Beers" and then confirm my work with my phone app. However, my measured gravities are not even close to matching up.

My most recent recipe, using the most conservative gravity values from the book and a mash efficiency of 60%:
2.6kg LME = 5.72 lbs * 37 GU * 100% efficiency = 212 GU
0.6kg crystal = 1.32 lbs * 33 GU * 60% efficiency = 26 GU
0.25kg malted wheat = 0.55 lbs * 37 GU * 60% efficiency = 12 GU
0.25kg chocolate = 0.55 lbs * 25 GU * 60% efficiency = 8 GU

Total = 258 GU

/ 5 gal = 1.052 expected OG

However, I've made this recipe twice and the first time I got an OG of 1.032 and the second I got an OG of 1.036. Even if the grains didn't mash at all (and really, I'm steeping in this case; they're heavily modified) I should still get an OG of 1.042 from the extract. I'm not complaining toooo much in this case because this beer turned out delicious, but if I'm going to keep making recipes I need to know where I went wrong. HELP!

[jeffsmith]

Are you using a hydrometer to measure your gravity? Are you correcting for temperature? How is your pre-boil gravity looking?

Those questions should help us pinpoint your problems.

[Ladd]

Are you using a hydrometer to measure your gravity? Are you correcting for temperature?

This is likely the culprit. If you are checking your wort at steeping temps (170°F) and getting 1.036 that would be somewhere around 1.061 with a temperature adjustment. Beersmith provides a tool for temperature adjustment but I find it more accurate to cool the hydrometer sample down to room temp before taking the reading.

[IanWatson]

Sadly, I did take my gravity reading at pitching temperature. Any correction would be minor (though I'm fairly certain I remembered to correct). It was done with a different hydrometer for each batch. Each batch also had a different source of LME and grains (NG for the first, Everwood for the second).

I didn't take a pre-boil reading.

[RubberToe]

Are you allowing the LME to be completely mixed in?

Is your final volume accurate?

[CorneliusAlphonse]

accurate volume measurement is very important. Also, that is only 3.7 kg of malt; I'd usually expect to use 4 to 4.5 kg to get a beer in the 1.050-1.060 range

Edit - just realized that some of that was LME. I'd guess accurate post-boil volume measurement is likeliest cause

[Bowserm]

If you are only steeping the grains, you don't really get much sugar out of it. Are your grains being milled? What is your "steep/mash" temperature?

When I first started, I made a 1.023 stout because I didn't crush the grains and my temperature was all over the place.

[IanWatson]

I think my final volume is accurate. At least +/- 250ml I would say. Just for clarity, my post-boils procedure:
- Allow wort to cool to close to pitching temp
- Transfer wort to wide-mouth carboy
- Top up to 19L with cool water
- Take gravity reading
- Pitch

Grains were crushed at the store in both cases. The steeping took place at ~155F, but wasn't all that stable. I managed to keep it in the range of 152 - 157F. The thing though is that for this recipe the grains are highly modified, so as I understand it I should be getting the sugars just from steeping, no? I.e. there's really no conversion from starch to sugars going on.

I'm brewing a batch tonight. It's a different recipe, but I'll pay close attention to everything and see if I hit close to target gravity, or if I'm way off again. That may provide more information...

[Broob]

Did your estimated initial gravity calculation account for the topping up of volume?

[CorneliusAlphonse]

When I pop your numbers in this calculator it gives me results pretty similar to what you got. Think you might be calculating the stuff wrong (I've never done it by hang)
http://www.brewersfriend.com/allgrain-ogfg/" onclick="window.open(this.href);return false;

[IanWatson]

When I use that calculator I get an OG of 1.050, with is just barely off the 1.052 I got by hand.

[IanWatson]

P.S. I appreciate all the replies and suggestions to date!

[CorneliusAlphonse]

roger. i did too on second effort.

Only other question I have - how do you have the carboy graduated? If you used the gallon markings on the side of a bucket, they are in imperial gallons - so 5 gallons is actually 5 imperial gallons (about 23 litres), not 5 us gallons (19 litres). Sorry to harp on about the volume measurement!

[IanWatson]

I've taken to skipping the bucket altogether and just going straight to my (wide-mouth) carboy, unless I'm making a beer that really demands a secondary. I determined the 19L mark by filling up with measured water first.

Last night I made a wheat ale. I couldn't find my hydrometer, so I couldn't check my work... but I did pay attention to more of the details this time. One of the things I noticed was that there was still quite a bit of "goop" coming from by grain bag when I handled it after the mash. I kind of wonder if I'm not doing enough of a sparge on the grains and am leaving a lot of sugars behind. Is it conceivable that a significant amount of gravity could be locked up in the residual grains?

[LeafMan66_67]

I've taken to skipping the bucket altogether and just going straight to my (wide-mouth) carboy, unless I'm making a beer that really demands a secondary. I determined the 19L mark by filling up with measured water first.

Last night I made a wheat ale. I couldn't find my hydrometer, so I couldn't check my work... but I did pay attention to more of the details this time. One of the things I noticed was that there was still quite a bit of "goop" coming from by grain bag when I handled it after the mash. I kind of wonder if I'm not doing enough of a sparge on the grains and am leaving a lot of sugars behind. Is it conceivable that a significant amount of gravity could be locked up in the residual grains?

When you say "goop" coming from the grain bag, it tweaked something. Are you adding your LME while your grain bag is still steeping? If so, could you be pulling out a portion of your LME with the grains?

[IanWatson]

No, I wait until starting up the boil to add the extract.

A couple of days ago I made an APA and paid close attention to details. My expected gravity was 1.052. My (temperature corrected) measured gravity was 1.042. Better than my brown ale, but still fairly far off. HOWEVER, I did find out I've been reading the hydrometer wrong, so the actual gravity was 1.044. So that's one source of error gone...

[LiverDance]

have you tried mixing just a known amount of extract into a know amount of water and seeing what gravity it gives you? Seems like you are not getting what you should out of the extract.

[LeafMan66_67]

I've started to make my own recipes. I typically do 5 gal BIAB partial mash/steeping. I've been calculating the expected gravity per the methods of "Designing Great Beers" and then confirm my work with my phone app. However, my measured gravities are not even close to matching up.

My most recent recipe, using the most conservative gravity values from the book and a mash efficiency of 60%:
2.6kg LME = 5.72 lbs * 37 GU * 100% efficiency = 212 GU
0.6kg crystal = 1.32 lbs * 33 GU * 60% efficiency = 26 GU
0.25kg malted wheat = 0.55 lbs * 37 GU * 60% efficiency = 12 GU
0.25kg chocolate = 0.55 lbs * 25 GU * 60% efficiency = 8 GU

Total = 258 GU

/ 5 gal = 1.052 expected OG

However, I've made this recipe twice and the first time I got an OG of 1.032 and the second I got an OG of 1.036. Even if the grains didn't mash at all (and really, I'm steeping in this case; they're heavily modified) I should still get an OG of 1.042 from the extract. I'm not complaining toooo much in this case because this beer turned out delicious, but if I'm going to keep making recipes I need to know where I went wrong. HELP!

For this recipe, if I enter it into Beersmith as an Extract Brew with steeping grains, I get 1.042 as the OG. The same recipe as Partial Mash shows 1.053 OG. I realize that in your shows an OG of 1.036. From your latest post, you indicted an expected OG of 1.052 and got a measured of 1.042 or 1.044 - is there a chance that your calculations or your phone app is a bit off, and geared more toward an all grain brew? Just throwing it out there ...

As a side note, I have used Beersmith for Extract with steeping grains in the past with great accuracy, within a gravity point or two.

[IanWatson]

So as a follow-up to this, the answer is that I didn't understand the difference between steeping and partial mash. After reading this article I saw my mistake:

http://byo.com/malt/item/1582-what-exac ... hot-water?

I was "mashing" my grains in almost two or three times the volume of water than I should have been, so the enzymes weren't actually doing any converting, and I was actually just steeping. To make excuses, I'll say that none of the brewing books I've read made the difference between the two methods explicit, though to be fair I should have figured it out based on chapters about mash water volume. I did my advent beer last weekend as a proper partial mash and hit my OG almost perfectly.

[darciandjenn]

I agree that people use the term "partial mash" inappropriately when they are actually referring to grain steeping. It can lead to very confusing conversations. Anyway, glad to hear you've got your issue sorted!