All grain gravity is it 'real'

delboy · Post by **delboy** » Mon Mar 26, 2007 2:24 pm

Was thinking about this the other day. I've noticed that when i take a sample of the wort and cool it down to 20C i get high hydrometer readings. But when i left the same sample sit overnight which allowed the trub to completely fall out of suspension the reading was way down, is it possible that we are kidding ourselves about the gravity/fermentables in our beers.
There is ceratinly a lot of proteins in solution when coming out of the mash which will raise the gravity at that point, after boiling there is lots of insoluble proteins floating about to raise the gravity. After pitching there is lots of yeast in suspension to raise the gravity. Surely the boiled sample left overnight to allow trub to fall out is giving the real gravity from sugars ie quite a lot lower???
Somebody reassure me!!

PieOPah · Post by **PieOPah** » Mon Mar 26, 2007 2:29 pm

I think that the best way to know for sure is to take you sample and measure the gravity.

Remove the hydrometer and take readings ever few hours to see whether the reading changes (adjusting for temp changes).

Keep the sample covered to avoid evaporation.

Do not leave the hydrometer in the sample.

Post result

delboy · Post by **delboy** » Mon Mar 26, 2007 2:38 pm

I noticed this by mistake after a long day brewing i overlooked the trial jar and hydrometer in the clean up. The hydrometer was left in the jar can't imagine there was much evaporation and if there was it would have pushed the gravity up not down. The temp doesn't change much in the kitchen it sits at about 19C not enough to significantly alter the reading (and again being a degree cooler would slightly raise the gravity, i think?).

PieOPah · Post by **PieOPah** » Mon Mar 26, 2007 2:43 pm

I have also noticed the change in gravity readings when the hydrometer has been left in the jar for a prolonged period of time. I normally take a reading with my refractometer which in general agrees with my hydrometer reading. One thing I have never tried though is to take a refractometer reading after the gravity reading has changed.

Again this would be another 'test' that could be performed to see if there is any noticeable difference.

IIRC I have left a sample of fermenting wort and this has also changed reading after being left too long. Might be wrong in that though!

delboy · Post by **delboy** » Mon Mar 26, 2007 2:48 pm

POP it would be good if you could try the refractometer 'expt' with the before and after cleared wort.
I've used a refrac a few times for CsCl gradients but i don't know if proteins would significantly affect the readings (ie deionsed distilled water and pure CsCl being used in my case)??

PieOPah · Post by **PieOPah** » Mon Mar 26, 2007 3:01 pm

Next time I get a chance to brew I'll give it a try. Might be a while though since my next brew day has been postponed due to it clashing with the sale of Glastonbury Tickets (not allowed to do anything else other than try and buy the tickets!)

delboy · Post by **delboy** » Mon Mar 26, 2007 4:00 pm

Hi POP
Just realised that refracts are routinely used to measure blood serum levels (the proteins in the blood bend the light just like sugars to give you quantifiable readouts). I'm guessing thats why your hydro and refract readings are roughly in agreement (in light of the above it really would be interesting to see how the overnight clarified wort compares on the refract).

UserDeleted · Post by **UserDeleted** » Mon Mar 26, 2007 4:07 pm

This has been discussed to death on the US Homebrew Digest, and the upshot of it is yes the other stuff suspended in the wort will affect the hydrometer reading. The more stuff suspended the more the reading is affected.

Protien has a minor effect on a refractometer, Alcohol/yeast quite a bit more, but in these cases it tends to make the 'line' fuzzy' rather than way wrong.

BarryNL · Post by **BarryNL** » Mon Mar 26, 2007 4:23 pm

delboy wrote:Was thinking about this the other day. I've noticed that when i take a sample of the wort and cool it down to 20C i get high hydrometer readings. But when i left the same sample sit overnight which allowed the trub to completely fall out of suspension the reading was way down, is it possible that we are kidding ourselves about the gravity/fermentables in our beers.

I normally put the sample through a coffee filter paper first. Actually, I should try before and after readings with this technique to see how much difference it makes...

delboy · Post by **delboy** » Mon Mar 26, 2007 4:25 pm

Surely if refractometer readings are used for the detection of proteins for clinical applications they must be reasonably sensitive to them and would'nt just 'wobble the line'.
Can't see that going down well 'yes Mrs miggins you do indeed have an incurable blood pathology just look at the fuzzy woobly line we got for your blood parameters'

.

Any links to the homebrew digest were its been talked to death (its still of interest to me because i haven't read them yet).

I'm seeing significant drops so the upshot is when i say taste this beer i brewed at 5.5 % what i really mine is check out this beer i brewed at 4.0%, or check out this barley wine but watch out at 5.5% it really has a kick .

Post by **Andy** » Mon Mar 26, 2007 4:27 pm

We're using cheapo refractometers off Ebay, doubt if the NHS get theirs via that route...

delboy · Post by **delboy** » Mon Mar 26, 2007 4:38 pm

There is a lot of protein in the wort i'd be surprised if it wasn't affecting the reading even on the el cheapo models

.

I hope im wrong because i really did believe i was making 6.0% and 5.5% beers it'll be a bit of a dissapointment to find out they are a shadow of that.

Post by **Andy** » Mon Mar 26, 2007 4:44 pm

Based upon the state of my head on most Saturday mornings I conclude that my gravity readings are reasonably accurate

delboy · Post by **delboy** » Mon Mar 26, 2007 5:05 pm

Have to say since i moved to AG my hangovers have disappeared

. Thought it might have something to do with a cleaner ferment (ie all the nutrients that the yeasties need in the wort).
Maybe its because i was drinking 3.5% etc

.

On the plus side surely im justified in drinking the beers a week or two sooner what with them being lower in gravity

.

SteveD · Post by **SteveD** » Mon Mar 26, 2007 5:07 pm

Hic..and minesh

Sodium Met affects gravity too. My pot of Sodium Met solution where I kept thermometer, hydrometer, etc, had a gravity of about 8. The crux of what your saying is 'Does dissolved protein affect gravity?' Once it has come out of solution it wouldn't affect it. Solids don't AFAIK. But, while dissolved, I expect it could well. If Sodium Met does, then why not protein?

I really loved the asthmatic wheezing attacks brought on by Sodium Met, but have switched to Idophor becasue it's such a nice colour

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All grain gravity is it 'real'

All grain gravity is it 'real'

Re: All grain gravity is it 'real'