Can my tap water be of 1.003 gravity?

[Finlandbrews]

Is it possible that my water has a 1.003 gravity? If so, why/what could it be?

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[Altrez]

Have you tested the TDS of your water? My water shows just a bit over 1.001 at room temperature. Test your meter with distilled water it should show 1.000.

-Altrez

 

[ajdelange]

It is possible. As you can see 1.003 SG corresponds to ~ 3/4 Bx which implies a sucrose content of 3/4% w/w or 7.5 g/L. Assuming that more typical minerals behave roughly the way sugar does that would imply TDS of about 7500 ppm. That should answer your question.

But you aren't measuring specific gravity here. You are measuring refractive index and interpreting RI as sugar content.

The most likely explanation is that your scale is out of alignment. Most instruments have some sort of adjustment screw that will let you align it to a substance of known RI. Here that substance is water with nothing dissolved in it. Note that temperature is important. The calibration must be done at the temperature specified for the instrument.

Note also that refractometry isn't a particularly good way to estimate the specific gravity of wort for reasons that have been discussed here extensively.

 

[b-boy]

Get some distilled water and test it. If it doesn't read 1.0000, adjust the instrument. There is a small adjustment screw in the device. It probably shipped with a screwdriver as well. Retest your water and see what you get.

If you're concerned about your water, you can always use distilled or RO water as a base.

A refractometer works fine for measuring wort. The measurement will be off after fermentation due to the effects of alcohol. The FG measurement can be corrected using a formula or calculator. Both can be found online. I've used both a refractometer and a hydrometer. I've gotten very good results from both devices. There is a certain amount of error you'll see from either device. Either is accurate enough for most home brewers.

 

[Finlandbrews]

It is possible. As you can see 1.003 SG corresponds to ~ 3/4 Bx which implies a sucrose content of 3/4% w/w or 7.5 g/L. Assuming that more typical minerals behave roughly the way sugar does that would imply TDS of about 7500 ppm. That should answer your question.

But you aren't measuring specific gravity here. You are measuring refractive index and interpreting RI as sugar content.

The most likely explanation is that your scale is out of alignment. Most instruments have some sort of adjustment screw that will let you align it to a substance of known RI. Here that substance is water with nothing dissolved in it. Note that temperature is important. The calibration must be done at the temperature specified for the instrument.

Note also that refractometry isn't a particularly good way to estimate the specific gravity of wort for reasons that have been discussed here extensively.

Thank you for all these comments, very valuable? Ajdelange, is 1 Bx equivalent to 4 points gravity and 20 grams of sucrose per litre?

I have not measured my TDS in water, why is it important? My water comes from a reverse osmosis plant 300 meters from my house btw.

Why is a hydrometer better than a refractometer in short? I have a hydrometer but no wine thief yet so I have not been able to sample quantity necessary to fill my hydrometer tube.

Is temperature important too if the refractometer is an ATC one?

 

[b-boy]

Is temperature important too if the refractometer is an ATC one?

I have an ATC refractometer. The only issue I've had with temperature is when it's extremely cold. I get nonsensical readings below freezing. I just run in the house to warm it up, and it's fine.

 

[ajdelange]

..is 1 Bx equivalent to 4 points gravity and 20 grams of sucrose per litre?

Approximately and it depends on where you are in the Brix scale. It is a close approximation. But 1 Bx means 1% sucrose by weight. Thus 1 kg of sucrose solution of strength 1 Bx would contain 10 grams of sucrose. In order to obtain the number of grams per liter you need to know the specific gravity of the solution as well as its strength in Bx. There are tables that list the specific gravity of sucrose solutions as a function of their strength in Plato (same as Bx). For example a 10 °P solution has specific gravity 1.04003 relative to water at 20 °C. This gives you an idea as to how close the 4 points to 1 °P relationship is in the range of OG's of the beers we typically brew. For comparison 1 °P wort has SG = 1.00389. Still a pretty good approximation.

So 1 kg of 10 °P wort contains 100 grams of extract. It's volume is 1/1.04003*998.203 where 998.203 is the density of water (kg/L) at 20 °C and the weight of 1 L of this wort is thus 1.04003*998.203 of which 10% is extract so 1 L holds 0.1*1.04003*998.203 =103.816 grams/L.

If you were to do the same for a 1 °P solution you would find the sucrose content to be 0.01*1.00389*998.203 = 10.021 grams/L. Thus the extract content of worts at 10° P is 10.38 grams/L/°P and at 12 °P it is 10.47 so you could use 10.4 for most beers.

I have not measured my TDS in water, why is it important? My water comes from a reverse osmosis plant 300 meters from my house btw.

A poster suggested that if there were a lot of solids dissolved in your water it could explain the refractometer reading of 0.75 Bx. I then pointed out that the dissolved material would have to be at a TDS level of thousands of mg/L and that, therefore, it isn't dissolved material that explains what you see.

Why is a hydrometer better than a refractometer in short?

In short it is because refractometers will give you readings that are off by 1 - 2 Bx and there is no way to know which worts are going to do that in advance. Most of the time they do better than that being within 0.5 Bx or so but it didn't take too many wild readings to convince me I should leave the refractometer in the drawer.

The reason behind this is that both hydrometers and refractometers are calibrated with sucrose. Wort doesn't contain much sucrose. Density of sugar solutions doesn't depend that much on which sugar is involved. Even soluble starches track the Plato table well. The same is not apparently true of RI.

Is temperature important too if the refractometer is an ATC one?

Yes, very much so. Temperature compensation in the handheld optical refractometers is a crude adjustment of the prism by a bimetal spring. It is calibrated for the variation in RI for a sucrose solution and evidently doesn't match the other sugars very well. If you are using an ATC refractometer be sure to use it at the temperature for which the correction is 0.

 

[hatterdude]

I've switched through a few different water supplies throughout the years and have always calibrated "0" to tap water instead of distilled water. I figured it was more valuable to reference the actual water I was using as opposed to distilled water. Of course it means I have to read my FG using the refactometer and then do the calculations to adjust (as the hydrometer would show me .003 points higher).

Not sure if this is the "right" approach. One advantage is when reviewing my old brewing logs I don't have to make adjustments for where I was living at the time (at least I hope I don't have to!).

Any thoughts?