Hydrometers, distilled water, and calibration

Quick question, as I have not seen this info posted anywhere before:

For a correctly calibrated hydrometer to register 1.000, you must use distilled water ( I get 1.004 in my tap water). But since I BREW with tap water, shouldn't I be subtracting .004 from the readings in my beer?

I assume that all those minerals still make it through the mash, sparge and boil into the fermenter, right?

That is some pretty dense tap water. If you measure distilled water and your tap water at identical temperatures do you really observe a .004 difference?

Are they both at 60F?

remilard said:

That is some pretty dense tap water. If you measure distilled water and your tap water at identical temperatures do you really observe a .004 difference?

Click to expand...

temp is important. my ground/tap water floats at 1.000. It would seem to me that distilled would be lighter, not sure though

yes, the tap water was at 60° - reading measured from the bottom of the meniscus.

Welll, if it's off by .004 then that's your correction factor.

I don't know what else to tell you.

Maybe I'm not being clear: the hydrometer is CORRECT if you use distilled water (which is how every hydrometer calibration tutorial tells you to do it). So it reads correctly at 1.000 using distilled water, but there are minerals and such in my tap water which cause a .004 higher reading.

My question is should I adjust for this when brewing with the same tap water, making the assumption that all these minerals make it through the final boil into the fermenter, thus causing a .004 higher reading in the finished product?

Most tap water has an SG of 1.000. Your water has 15% as much difference from pure water as does sea water. It is hard to imagine that would be drinkable.

I'll double check them again tonight against some distilled water. They read 1.000 when I last checked them with distilled water several months ago, but just checked the tap water last night....

Well, disregard this post....

Just recalibrated in distilled water and both are reading at 1.003, while they read 1.004 in tap water. I didn't think that hydrometers could shift out of whack, but perhaps I screwed up when I checked them in distilled water months ago

They also read 1.085 in 1.083 wort.....So rather than doing some tricky math every time I'm just going to take the average and subtract .003 from all measurements.

Sorry for wasting everybody's time.

You could try boiling some tap water for 10 minutes, cooling to 60 and then checking with the hydro. That should tell you if any of that will make it through the process and will need to be adjusted for.

My guess is that the difference is small enough not to worry much about.

ifishsum said:

You could try boiling some tap water for 10 minutes, cooling to 60 and then checking with the hydro. That should tell you if any of that will make it through the process and will need to be adjusted for.

My guess is that the difference is small enough not to worry much about.

Click to expand...

Yeah, even with my OCD I think I can handle being a point off