Calibrating Hydrometers... Are you *sure* it's stuck?

[lancsSteve]

4th brew in a row that's stuck at 1.020 - NOT happy...

This one was an altbier-esque thing, fermented cool with two packs of nottingham(14c) crazy airlock activity then all quiet on the western front and stuck at 1.020, expected FG 1.012

Same happened with my steam beer with recultured yeast so I added a pack of nottingham and roused it which saw fermentation kick off a little but no further gravity drop - figured it tasted nice, decent bitterness, would be fine if cooled and carbonated in a cornie... just rechecked it for FG having let it go flat and warm up to 20c:



And my schwartzbier...

With both of those I roused the yeast, added some yeast nutrient and raised the temp to try and get those last few points to drop... All seemed VERY consistent and was putting it down to something to sort out... then I got my other hydrometer back the other day (it had been in a demijohn to take gravity of a beer fermenting in their in too small an amount to rack off and test).

Thought I'd go for a 'second opinion' - same beer, same temp, same flatness:



Now - I've tested/calibrated BOTH of these at 20c in water. The latter one reads a little under at 0.998 the former reads a little high at 1.002 but we're looking at 8 POINTS DIFFERENCE here, not 4!

Am both relieved (my beers are all fine and not sticking) and perplexed at just how far out these are and how far out 'calibration' is...

[Andy]

Moved to AG Brewing Q's and A's.

[lancsSteve]

Moved to AG Brewing Q's and A's.

Thought it related more to kit issues than a question about all grain...

[Andy]

Ah, sorry - thought you were an AG brewer. The original thread was in "Brewing Equipment" BTW

[lancsSteve]

Ah, sorry - thought you were an AG brewer. The original thread was in "Brewing Equipment" BTW

Where the hydrometer correction info is - badly titled thread, either place is fine as it's more a !!!! !!!! about equipment than a question to be resolved...

Retitle - maybe Are you sure your brew is stuck high???

[HighHops]

Hi Steve

I've got two hydros that do the same thing. One reads 6 points lower than the other, but it's linear it measure water at 17C as 994 instead of 1000. I think it changed when I flicked water off after washing and the paper inside the glass tube moved.

I'd love to find one with the numbers etched/engraved on the glass. I can only find cheap paper inside glass ones on tinternet or big bulky metal ones with weights on.

[Ditch]

Steve; Throw the bit of glass crap in the bin. Drink ye beer. Get pissed. Be happy. K?

[onelegout]

As hightops said - first thing to check is that the paper inside hasn't moved. I've taken a photo of my hydrometer when I bought it so that if I have any odd readings I can check there's been movement

P.S just signed that with a kiss - too much langhams 'hip hop' and harveys 'old ale' methinks!

[lancsSteve]

Paper doesn't seem to have moved - I've enjoyed the beers and am mega-relieved they weren't all stuck. I have the fear now about checking thermometers next usually just as bad.

So - anyone know of any more reliable hydrometers or ways of measuring this? As I use an airlock this has always been based on airlock activity going to zero and then being phased by the 1.020 reading... Half the riddle solved but accurate gravities are kind of important!

[steve_flack]

Just to be certain here....these are AG beers aren't they. If so check the thermometer you use to measure mash temp. A couple of degrees out there and you could be mashing at 70C and that's a really good way of getting a low attenuation beer (I know I've done it intentionally).

[lancsSteve]

Just to be certain here....these are AG beers aren't they. If so check the thermometer you use to measure mash temp. A couple of degrees out there and you could be mashing at 70C and that's a really good way of getting a low attenuation beer (I know I've done it intentionally).

These are AG beers - the key point hough is the two pics above are of THE SAME BEER!

When everything was 'sticking' at the same gravity I was thrown and about to post up here looking for where I'm going wrong, hopefully someone would have said 'check your hydrometer' rather than 'what's your water profile / mash tempo etc. etc. as those are blind alleys'

So thought I;d share this and chalk another thing to experience to share here: if it tastes good but reads wrong check your kit before you spend an age tracking down a ghost in the process. I think it's VERY easy to blame yourself and inexperience / problems / and not re-consider that your kit may be the 'problem' in itself. I'd never have known without another hydrometer to check it against. As mentioned these were both 'calibrated' at 20xc in water with one reading a little under and one a little over, 4 degrees difference, but in wort (left to go flat so not bouyed up by bubbles) at 20c I'm getting 8 degrees difference!!!

2 degrees of that could be 'rationalised' as reading top of miniscus or surface level... But 8 degrees difference between 2 pieces of kit in the same wort is a huge margin of error...

Unfortunately this also means there's a problem with all my records too

Next I'm going to have to start checking thermometers as these are notoriously inaccurate

[steve_flack]

Oh I see. My fault for not reading it more closely.

Anyway, yes, cheap hydrometers are about as accurate as cheap thermometers - i.e. not very. As always you can spend a decent wedge of money on a HMRC approved hydrometer but you'll get real mad when you break one of those.

I have a calibrated thermometer which basically means it came with a bit of paper telling me how wrong it was (in my case - it's spot on). I have to admit I tend to rely on a refractometer for gravity readings. It's not that accurate either but it tells me all I need to know.

[CJBrew]

Unless you're selling the beer* the absolute gravity reading doesn't matter. The important thing with a hydrometer is the relative difference between readings.

If you assume the scale is linear and correctly divided (IMO a reasonable assumption) you can either calibrate zero against pure water at the right temperature or just rely on the difference of two readings... that's what you use for ABV calculation in any case.

* although if you were you'd probably need to use approved kit, I think tax is based on ABV so as long as your OG and FG readings are equally low/high your final ABV should be accurate.**

** As long as you're within the linear limits of the hydrometer; I imagine they don't work accurately for _very_ high gravity worts or spirits.

[lancsSteve]

Unless you're selling the beer* the absolute gravity reading doesn't matter. The important thing with a hydrometer is the relative difference between readings.

Which is important and unfortunately I don't have OG readings from both hydrometers to see that. But thinking of it like that is a useful shift in perspective... IF it's linear which brings me on to:

If you assume the scale is linear and correctly divided (IMO a reasonable assumption)

That's my BIG question - is the scale linear? It isn't for temp correction and what I'm getting here is 4 points difference at 1.000 but 8 points at 'the gravity somewhere between 1.012 and 1.020 shown above). So extrapolating from this will I get 16 points at 1.040 or the same 8 point difference... THe next step of testing is obviously

you can either calibrate zero against pure water at the right temperature or just rely on the difference of two readings... that's what you use for ABV calculation in any case.

But that's part of my question - I 'calibrated' at 1.000 in tap water at 20c and got 4 points difference but measures of fermented wort at 20c giving readings of 1.012 or 1.020 I get 8 points difference so the 'calibration' isn't so close here - that's a non-linear scale if differences are differences at dif densities. I guess my temps could be different but these two reading were taken immediately after each other as were the water readings so no change in temp between reaidngs but a possible slight temp dif between wort and water readings. Will have to try on some wort at OG and chart change on both hydrometers to see what's happening.

[bosium]

Steve, sorry if you've answered this already, but are both of your hydrometers calibrated to 20C? I know both of mine are (I also have two so I can get a second opinion, thermometers too), but some are calibrated to 16C so it's worth a check.