6 replies to this topic

[The Brew Dude]

One of my pyments is approaching target FG. It's hard to get a Hydrometer reading in the tube due to the fizz caused by continued fermentation. Best I can read is 1.026-8.Using Hightest's "clarifying" method, I get a reading of 14B. If I put an OG of 1.120 and a current fermenting Brix of 14, I get an actual SG of 1.017.These readings are 10 points apart.Suspicious, I tested my refractometer with distilled water. It came out at 0B.Which do I trust?

[Wayne B]

I'm not a refractometer expert, so I always trust the hydrometer! I think that Hightest will have to answer this.

[MtnBrewer]

One of my pyments is approaching target FG. It's hard to get a Hydrometer reading in the tube due to the fizz caused by continued fermentation. Best I can read is 1.026-8.Using Hightest's "clarifying" method, I get a reading of 14B. If I put an OG of 1.120 and a current fermenting Brix of 14, I get an actual SG of 1.017.These readings are 10 points apart.Suspicious, I tested my refractometer with distilled water. It came out at 0B.Which do I trust?

Did you also check your hydro w/ distilled water? Sometimes the scale can slip up or down. For what it's worth, I get the same computed gravity that you do. I know how hard it can be getting a good hydro reading when there are bubbles clinging to the hydrometer and for that reason, I think I'd trust the refrax reading more. Did you try spinning the hydro to get the bubbles to let go?

[The Brew Dude]

Did you also check your hydro w/ distilled water? Sometimes the scale can slip up or down. For what it's worth, I get the same computed gravity that you do. I know how hard it can be getting a good hydro reading when there are bubbles clinging to the hydrometer and for that reason, I think I'd trust the refrax reading more. Did you try spinning the hydro to get the bubbles to let go?

Yes, but they just kept coming. :)Tested the hydro with distilled water. Got 1.002. It's off a bit, but still only by 2 points, not 10.I think I'm going to be using the refractometer more. The method HT uses seems to remove the bubble issue and gives a nice clean line.

[Hightest]

Using a refractomer during fermentation to determine SG is my preferred measurement method. I have periodically checked the spreadsheet function with comparative final gravity hydrometer (an expanded scale hydrometer) readings and found them to correlate well.However when using this method, it is CRITICAL that an accurate OG be determined. Also, since a very small sample volume is used with a refractomer, any moisture (or prior sample residual) in the sampling device can easily skew a reading. That is why I use disposable pipettes - discarded after each sample (never reused).

[The Brew Dude]

Using a refractomer during fermentation to determine SG is my preferred measurement method. I have periodically checked the spreadsheet function with comparative final gravity hydrometer (an expanded scale hydrometer) readings and found them to correlate well.However when using this method, it is CRITICAL that an accurate OG be determined. Also, since a very small sample volume is used with a refractomer, any moisture (or prior sample residual) in the sampling device can easily skew a reading. That is why I use disposable pipettes - discarded after each sample (never reused).

Yup, that's the method I use. I even blogged about it back in the day.Going forward, I will stick to the refractometer method.For this instance, I did get a good reading on the original must, fizz-free.

[Brewer Pete]

I use refractometer exclusively when doing my Meads, I have a quality Scottish hydro for beers.Another bad point about reusing pipettes is if you let them sit and dry a bit before cleaning you'll have residual sugars as well as potential moisture between uses.Even though 2mL, you still get some room with the plastic pipette to tip it up and let the air in the bulb end escape so you can rattle it back and forth between your fingers in an attempt to degass the sample.With a heavy krausen, you'll get globs of floating yeast stuck to the outside of the pipette which gets yeast cells into your sample drops if your not cleaning it up first.If you have an accurate OG then you can run the current B-RDS reading through an ethanol compensation formula to bring the skewed reading back into line with actual gravity. This step is pretty critical as if you do a reading later into fermentation your answers are further and further away from actual gravity and will be further and further in disagreement with a hydro reading. Both hydro and refractometer are analogue instruments and have tolerance error factors in their reading, its common for both to not agree exactly but be off by the error margin percentage. The same with the math formulas, they get errors out in to the 3rd and 4th position after the decimal if they are decent formulas. That still hits close to brewing points range, but the error rate in the instruments plays far more havoc than a decent formulas error rate.BP