Strange gravity readings when BIAB

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chefgage
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Strange gravity readings when BIAB

Post by chefgage » Sun Oct 30, 2016 5:44 pm

Recipe for BIAB no sparge full volume mash
1.1kg Maris otter
Amarillo hops - 7g 60mins
7g 15mins
12g 0mins

Total mash water 11.8l
After bag/grain removed 11.13l
Wort into fermenter 5l
3.4l left in boiler
So wort boiled off 2.73l (taking into account 0.67l lost due to grain absorbtion.

Hope thats enough info

Anyway the problem is I got a pre-boil gravity reading off 1.030, after boiling for an hour with just over 2.5l lost due to evapouration the post boil gravity was 1.030... THE SAME!

I am replicating a brew I did the other week using the exact same method and I got the same gravity readings pre and post boil.
When I have brewed before using three vessels I have not had a problem with the gravity readings i.e. gravity goes up after boiling. ISo this is the second time this has happend. I have checked the hydrometer at 20'c which reads 1.000

Any idea why the gravity does not change during boiling???

Also the BIAB i did the other week ended up at 1.005. SO it has fermented out ok.

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Sadfield
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Re: Strange gravity readings when BIAB

Post by Sadfield » Sun Oct 30, 2016 7:00 pm

Did you stir your wort before taking the Pre-boil measurement? I'm wondering if there was a degree of wort stratification occurring during any time there may have been spent draining the mash bag? Resulting in weaker wort at the top of your kettle, giving a false reading.

chefgage
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Re: Strange gravity readings when BIAB

Post by chefgage » Sun Oct 30, 2016 7:39 pm

Thats exactly what i have been thinking. I took both pre boil samples from a valve on the vessel after lifting the bag out. I did not stir it first :roll:

So I will do another one using the exact same method but give it a stir tahis time. I think the post boil gravity reading is correct, but the pre boil gravity will obviously be lower.

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Re: Strange gravity readings when BIAB

Post by aamcle » Sun Oct 30, 2016 10:24 pm

Have you carefully checked your hydrometer? Stratification is a possibility but the same each time seems odd.

Have you checked to find out what you should expect for the recipe and did you achieve it?

atb aamcle

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Sadfield
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Re: Strange gravity readings when BIAB

Post by Sadfield » Sun Oct 30, 2016 11:04 pm

Agreed, knowing the both target gravities would help.

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Re: Strange gravity readings when BIAB

Post by rpt » Mon Oct 31, 2016 9:38 am

I can't see how it can be the hydrometer as it should show a difference between pre and post boil gravities. You definitely should stir before taking the readings.

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Re: Strange gravity readings when BIAB

Post by chefgage » Mon Oct 31, 2016 10:53 am

I have checked the hydrometer at 20'c and it reads correct formjust water. I use beer smith for the recipes. The target gravity pre-boil should have been 1.031 and I achieved 1.030. Post boil it should have been 1.048 (i think, without having a look).

Anyway I think I am well down in efficiency terms and that the pre-boil gravity after I give it a good stir will be below 1.030. Which will then make my post boil gravity around the 1.030 mark.

I am going to brew this exact same one but give it a good stir after removing the bag. Hopefully that will clear this up. Like i said I have never had a problem when using three vessals but I take the pre-boil gravity from the boil kettle after transfering from the mash tun. At this point it is well mixed.

I will report back later in the week with the results.

smuggles

Re: Strange gravity readings when BIAB

Post by smuggles » Tue Nov 01, 2016 8:02 pm

Are you sure that 2.7L has been boiled off? That seems like quite a lot.

I only ask because when I put your numbers into brewmate it gave me a pre-boil gravity of 1.034, and a post-boil gravity also of 1.034. But that's with my typical evaporation rate of 9%. If I use your numbers for boil-off and dead space I would have an evaporation rate of 23%, pre-boil SG of 1.029 and post-boil 1.034. So, possibly if you're not boiling off as much as you think that would account for the gravity not changing.

If you definitely are boiling off that much then I have no idea. Unless, and apologies if this is a silly question, but did you adjust for temperature (or cool the sample to 20C) when taking the gravity readings? That's about the only other thing I can think of that might cause funny readings.

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Re: Strange gravity readings when BIAB

Post by chefgage » Wed Nov 02, 2016 11:55 am

smuggles wrote:Are you sure that 2.7L has been boiled off? That seems like quite a lot.

I only ask because when I put your numbers into brewmate it gave me a pre-boil gravity of 1.034, and a post-boil gravity also of 1.034. But that's with my typical evaporation rate of 9%. If I use your numbers for boil-off and dead space I would have an evaporation rate of 23%, pre-boil SG of 1.029 and post-boil 1.034. So, possibly if you're not boiling off as much as you think that would account for the gravity not changing.

If you definitely are boiling off that much then I have no idea. Unless, and apologies if this is a silly question, but did you adjust for temperature (or cool the sample to 20C) when taking the gravity readings? That's about the only other thing I can think of that might cause funny readings.
I based the boil off partly on what beer smith said i should have after removing the bag and what went into the fermenting minus what was left in the boiler. The next time i am gong to break out my trusty volume stick which i will recalibrate to the smaller keytle i am using.

So i am not totally sure on boil off but that will be checked tomorrow as doing these smaller batches allows me to do one per week :D The first time this happened i took all gravity reading at the higher temperatures and then adjusted for temperature using beer smith. The one after that i cooled the sample down to 20'c just to be sure but the same thing happened.

Anyway thanks for all the advice and suggestions, the main thing i need to do is stir after removing the bag before takng a gravity reading and also check the boil off is correct as you sugested

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Re: Strange gravity readings when BIAB

Post by chefgage » Fri Nov 04, 2016 9:05 am

Brewed this exact same recipe last night. I stired the wort after lifting the bag out and got a pre-boil gravity of 1.025. After boiling the post boil gravity was 1.033. So thats sorted the problem of the strange readinds! Just got to stir it.

Next problem is the low original gravity. According to beer smith it should have been a pre-boil gravity of 1.031. How much does the age of the grain effect gravity readings. I know i am doing the no sparge method but beer smith takes this into account. I am hitting the correct temperatures (from what it tells me on beer smith). So any ideas of why the pre-boil gravity is so low??

Forgot to add. I actually measured the boil off, it turned out to be 2l, so less than i thought.

AnthonyUK

Re: Strange gravity readings when BIAB

Post by AnthonyUK » Fri Nov 04, 2016 9:12 am

Are you able to measure mash pH and do you do any water treatment?
These two points if off will have more of an impact than a couple of degrees out on mash temp.

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Re: Strange gravity readings when BIAB

Post by chefgage » Fri Nov 04, 2016 9:22 am

I do not have the means to measure ph but it is one of the things i will be buying next. The only water treatment i do is put a crushed campden tablet in the heated water.

I am buying some hops in a bit so i might get something to measure ph. The water in our area is very hard.

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Re: Strange gravity readings when BIAB

Post by Sadfield » Fri Nov 04, 2016 11:11 am

Glad to see your moving forward with this. As you have the ability to brew quite quickly, you could try brewing with cheap bottled water from the super market (see tescos ashbeck) which has low levels of carbonates. This would give you a quick and cheap indication that alkalinity in your tap water is the issue.

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chefgage
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Re: Strange gravity readings when BIAB

Post by chefgage » Fri Nov 04, 2016 3:50 pm

Sadfield wrote:Glad to see your moving forward with this. As you have the ability to brew quite quickly, you could try brewing with cheap bottled water from the super market (see tescos ashbeck) which has low levels of carbonates. This would give you a quick and cheap indication that alkalinity in your tap water is the issue.

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I will try bottled water to see if this makes a difference. At least with all these small batches i am doing its giving me a good supply of beer, even if its not quite right

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Re: Strange gravity readings when BIAB

Post by chefgage » Thu Nov 10, 2016 1:09 am

Going to do the same recipe again this weekend. Had a look at the water quality information for my area and the calcium carbonate is 411.5 mg/l and is classed as very hard. The ph is 7.2

So i will take the advice and try using bottled water from asda ( eden falls) and see what difference that makes

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