Bloody Refractometer!

[Fourstar]

When I take gravity readings ( I usually only take og and fg.) I'll take a hydro and refrac just to compare the two and use the hydro sample for the refrac.

 

[RdeVjun]

Yep, last few posts have touched on something that's very important- one thing to bear in mind for tiny refractometer samples taken from the kettle is that they're losing quite a lot of water to evaporation in the few seconds between extraction, placement on the prism and it being closed for measurement. This concentrates the wort and leads to higher SG values when compared to hydrometer data.
I wondered for a long time why my refractometer data was usually higher than the hydrometer for kettle samples. Then I did a few experiments, confirmed that a large sample (say >1/2 cup) cooled in bulk and then sub- sampled for the refractometer was usually reading a bit lower, plus agreed with the hydrometer, than a few drops of hot wort cooled on a teaspoon and then placed on the prism. Ergo the the tiny sample's evaporation is not insignificant, so now I get a much bigger wort sample from the kettle and then sub- sample it for refractometer measurement once cooled. The pipettes didn't really help unless cooling a near- full bulb, but with boiling wort that's much easier said than done- it usually squirts right back out again!
The little stainless cup that comes with a domestic espresso coffee maker are ideal for sampling boiling wort, just fill, drop it upright in a container of water for rapid cooling and measurement.
My 2c, hope that helps! :icon_cheers:

Edit: Clarity.

 

[peaky]

I only use the refrac for measuring gravity during sparge, pre-boil, and measuring the OG. All other readings during fermentation are taken with a hydrometer. I like to drink the hydro samples during fermentation to get a little taste of what the beer will be like.

 

[Deebo]

Yep, last few posts have touched on something that's very important- one thing to bear in mind for tiny refractometer samples taken from the kettle is that they're losing quite a lot of water to evaporation in the few seconds between extraction, placement on the prism and it being closed for measurement. This concentrates the wort and leads to higher SG values when compared to hydrometer data.
I wondered for a long time why my refractometer data was usually higher than the hydrometer for kettle samples. Then I did a few experiments, confirmed that a large sample (say >1/2 cup) cooled in bulk and then sub- sampled for the refractometer was usually reading a bit lower, plus agreed with the hydrometer, than a few drops of hot wort cooled on a teaspoon and then placed on the prism. Ergo the the tiny sample's evaporation is not insignificant, so now I get a much bigger wort sample from the kettle and then sub- sample it for refractometer measurement once cooled. The pipettes didn't really help unless cooling a near- full bulb, but with boiling wort that's much easier said than done- it usually squirts right back out again!
The little stainless cup that comes with a domestic espresso coffee maker are ideal for sampling boiling wort, just fill, drop it upright in a container of water for rapid cooling and measurement.
My 2c, hope that helps! :icon_cheers:

Edit: Clarity.

Would wort being cooled inside a pipette evaporate? I'd assume it has no place to go and should be ok?

 

[RdeVjun]

Would wort being cooled inside a pipette evaporate? I'd assume it has no place to go and should be ok?

No, evaporation wouldn't be lost, so it can be a reliable solution. However have you ever succeeded in filling a disposable pipette with boiling wort? The wort squirts out the moment you invert it, I presume its because the small amount of relatively cool air that is trapped in the bulb expands considerably when the hot wort hits it, the only way out is back down the tube, taking most of the wort with it. At least that's been my experience, it is possible to fill one with some farting around but it usually negates most of the benefit in using one.

 

[Bongchitis]

No, evaporation wouldn't be lost, so it can be a reliable solution. However have you ever succeeded in filling a disposable pipette with boiling wort? The wort squirts out the moment you invert it, I presume its because the small amount of relatively cool air that is trapped in the bulb expands considerably when the hot wort hits it, the only way out is back down the tube, taking most of the wort with it. At least that's been my experience, it is possible to fill one with some farting around but it usually negates most of the benefit in using one.

Don't invert it then mate!

 

[RdeVjun]

Yeah, you could do that bongchitis, but it gets sort of tedious standing there continuing to squeezing the bulb while waiting for the wort to cool. Whether inverted or not, as soon as you release the bulb the wort will squirt out, at least that's been my experience with a few different sizes. Originally I thought they'd be the duck's nuts but alas they're really not that useful for hot wort.

 

[Bongchitis]

Yeah, you could do that bongchitis, but it gets sort of tedious standing there continuing to squeezing the bulb while waiting for the wort to cool. Whether inverted or not, as soon as you release the bulb the wort will squirt out, at least that's been my experience with a few different sizes. Originally I thought they'd be the duck's nuts but alas they're really not that useful for hot wort.

Sorry dude, didn't mean to sound like a cock.

With the pipettes I have If you hold it bulb up, squeeze bulb minimally , extract sample and then let the bulb return to its original position (excess bulb squeeze: air bubbles suck through wort and wort settles at bottom of pipette again). Nothing spills out! sample is enclosed and small and cools in no time.

If I invert i get the same fountain.

You may have a wider nozzle pipette than I and thus dribbles out the bottom.... dunno. Works for me though!

Cheers man.

 

[RdeVjun]

Nah mate, you're right, not getting worked up in the slightest! B)
There's probably loads of different pipettes out there, I just tried a few different ones I could lay my hands on- melted a few, had wort fountains out of others no matter how I tried and wasn't that enthused so gave up. Mind you, I've always felt that the wee stainless cup is a cracking tool for brewing anyway, so maybe I've got some bias! :icon_cheers:

 

[Deebo]

Haven't had the problem with wort shooting out either, I just grap a sample then chuck the pipette bulb side up in a glass (to stop any drips) and put it into the freezer for a short time. Works well for me. I use some fairly thin ones that came with the cheapo ebay refractometer.