Difference between refractometer and hydrometer readings

[bathman]

I have just been destemming and crushing my Cab Sauv and Shiraz grapes in the past couple of days. Ended up with 3 buckets of Cab must and 1 bucket of Shiraz must. I tested the sugar levels in all buckets initially with a refractometer and then the SG with a hydrometer.

However, the equivalent values between these do not tie up and I get a fairly consistent discrepancy, which would suggest it is not just human error in measuring. The results I got were:

Cab 1 - 22 Brix (refractometer), equivalent SG (according to online conversion tables) is 1.092SG
Cab 1 - 1.097 SG (hydrometer), equivalent Brix (according to online conversion tables) is 23.1 Brix

Cab 2 - 21 Brix (refractometer), equivalent SG is 1.0875SG
Cab 2 - 1.092SG (hydrometer), equivalent Brix is 22.0 Brix

Shiraz - 21.2 Brix (refractometer), equivalent SG is 1.0884SG
Shiraz - 1.093SG (hydrometer), equivalent Brix is 22.2 Brix

So getting a fairly constant 1 Brix discrepancy between refractometer and hydrometer measurements. Has anyone else had this discrepancy before and know why it is?

For calculating my potential alcohol is it best to use the refractometer or hydrometer reading?

Thanks!

 

[Ajmassa]

Look on the hydromteer for the calibration temp. All mine are calibrated at 60°. And if the actual temp is higher or lower the SG needs to be adjusted. I don’t know the actual math equation to convert tho. I just use an online wine calculator FermCalc. http://www.fermcalc.com/FermCalcJS.html. Could be partly to blame.

You can also check your hydrometer in distilled water. Should read exactly 1.0. I have a few hydrometers and one of them is off. Always reads about .004 high.
Both refractometer and hydrometer should be accurate for reading must sugar levels. Refract is nice since you just need a couple drops of sample. Once some alcohol is present however the refractometer will give false readings. And needs a conversion. Therefore Hydrometer is accepted tool once your fermenting.

 

[Johnd]

Seeing that your hydrometer reading is consistently off by one BRIX is a good thing, and not human error. It's highly possible to have a hydrometer that isn't perfectly calibrated at 25 Brix, but tests true at 1.000, and the opposite, many of us use two different lab grade hydrometers, one for high BRIX and one for low BRIX.

Not having two lab grade hydrometers, if I were confident that absolutely no fermentation has started, I'd trust the refractometer readings and make any desired BRIX adjustments based upon that. I'd then convert the refractometer reading to a starting specific gravity as a reference point. When fermentation was complete, I'd be using the hydrometer (because alcohol skews the refractometer readings) and making sure it was true at 1.000 by testing in distilled water. Calculating your final ABV is simple with a starting SG (converted from your starting BRIX) and a finished SG from a calibrated / adjusted hydrometer reading.

In any case, if you did nothing, being off by 1/23 would only make your ABV calculation off by roughly half a percent in the end.........

 

[mainshipfred]

This may or may not be the case or cause but recently I was having trouble getting an accurate SG on some freshly crushed must. I don't have a refractometer but was visiting a friend that did and used his reading which was also off by one brix. When I got back I forgot about my cylinder of must I left out and the bottom was full of sediment. I poured out as much of the cleaner must as I could which was almost enough for the hydrometer to float so I just added a little more not cleared. When I did the hydrometer test again it was a lot closer to the refractometer. Don't know if the thick sediment must had anything to do with it or not but that's what I'm going with.

 

[stickman]

The following data sample came from a certified lab conducting Juice Panels for the 2017 Washington vintage. The brix values are from refractometer readings, the glucose plus fructose values are from enzymatic method (just move the decimal over one place to the left to compare). With the exception of the early harvest Pinot, the refractomoter brix readings are all approximately 1 brix lower than the reportedly more accurate enzymatic values.

 

[Johnd]

The following data sample came from a certified lab conducting Juice Panels for the 2017 Washington vintage. The brix values are from refractometer readings, the glucose plus fructose values are from enzymatic method (just move the decimal over one place to the left to compare). With the exception of the early harvest Pinot, the refractomoter brix readings are all approximately 1 brix lower than the reportedly more accurate enzymatic values.


View attachment 51041

That’s very interesting, I’ve not seen any data like this before. Do you believe that this convention holds relatively true for refractometer vs actual sugar content? I’ve always been way more trusting of my refractometer for prefermentation sugar readings.

 

[stickman]

I believe it is true that generally the glucose plus fructose will be a bit higher than a refractometer reading, especially with high brix musts. The hydrometer and the refractometer both have issues as neither measures the values directly. The refractive index as well as the density of the solution is affected by all of the dissolved solids, not just the sugar. 1 Brix is supposed to be 1 gram of sucrose in 100 grams of solution so it is a weight percent. The glucose plus fructose enzymatic is closer to the true fermentable sugar content, but it is given in grams per liter so it is a weight over volume value. Because of the limitations of both the refractometer and the hydrometer, I would say just take your pick and stick with it. I've been going old school with the hydrometer for years, no particular reason, I'm just comfortable with it. The refractometer is still the standard in the vineyard, you just can't beat the convenience.

 

[balatonwine]

Did you test the calibration of your refractometer? Any decent refractometer should come with the option to adjust it. When I first bought mine, it tested it's calibration as per the manual it came with, and it was slightly off and I adjusted it accordingly. I routeanly test its calibration to make sure it is still accurate. And, yes, temperature of the must you are measuring is important for a hydrometer, which is why mine has a thermometer in it.

I also assume that the two measurements were taken with the refractometer and hydrometer at the same time. Because any delay, and if any fermentation had occurred between readings, would mean the refractometer reading is unreliable.

Personally, I use my refractometer as a testing tool. That is, to test samples to decide when to pick. Then use the hydrometer in the winery to measure the must at crush and press time. Because the hydrometer will be the tool to use during the rest of fermentation. So start and end with the same tool.

 

[bathman]

The following data sample came from a certified lab conducting Juice Panels for the 2017 Washington vintage. The brix values are from refractometer readings, the glucose plus fructose values are from enzymatic method (just move the decimal over one place to the left to compare). With the exception of the early harvest Pinot, the refractomoter brix readings are all approximately 1 brix lower than the reportedly more accurate enzymatic values.

Interesting, I wonder if that relates directly to the 1 brix lower reading I am seeing or if it is just coincidence? Either way it confirms it is perhaps not unusual to get a discrepancy between measuring methods.

Did you test the calibration of your refractometer?

Yep, it was fine

I also assume that the two measurements were taken with the refractometer and hydrometer at the same time. Because any delay, and if any fermentation had occurred between readings, would mean the refractometer reading is unreliable.

Yep, taken within 10 mins of each other, and from exactly the same sample of must, immediately after grapes were destemmed/crushed.

Thanks for all the responses everyone. Think I will stick to the hydrometer as that seems to be the recommendation, and plus it gives me a higher starting potential alcohol

Interestingly I did find this raised in a thread on this forum some years ago after doing a search, someone called RunningWolf said:

Bob as I'm going into vineyards and collecting grapes for testing, I check with a refractometer, brix hydrometer and test for ta. I almost always get up to a full brix difference between the refractometer and hydrometer. Use your refractometer in the field for a quick reference.

Full thread here: https://www.winemakingtalk.com/threads/hydrometer-vs-refractometer.33017/