An inaccurate hydrometer?

[robbyg]

Hi all - I've been lurking here for a couple of weeks, but I finally have a question that I don't see already answered.

I'm currently less-than-patiently waiting for my 5th batch, a extract-based blonde ale, to be ready to bottle. Before brewing this one, I decided to "invest" in a hydrometer (after reading dozens of Revvy's lamentations on the subject) to take readings, instead of just guestimating on fermentation completion and ABV percentages.

My OG reading for the blonde was 1.062... which was .005 higher than BeerSmith estimated for the recipe (which I'll post if it'll help). I took a reading again last night, two weeks in (early-ish yet, I know, but I was anticipating this one to ferment quickly), and it came out at 1.020... again, .005 higher than BeerSmith expected for a FG.

However, on a whim, I decided to just now test my hydrometer in pure tap water at the same temperature as my beer readings (68F, so I've been adding .001 to my readings)... and my water came in at 1.004.

So! Is my hydrometer off? Is my tap water amazingly buoyant? Am I not smart enough to read a floating bit of glass? What's going on?

 

[motobrewer]

tap water can be over/under 1.000. check it in distilled water.

but yeah, hydrometers can be off out of the box. and they can drift off over time. mine reads 2 points low.

 

[Wellshooter]

The rolled up paper scale inside the hydrometer has slipped. You can attempt to tap it back in place or subtract the difference. I think if your tap water is drinkable it should be closer to 1 than that. My water is hard but my hydrometer doesn't read but just a BCH more than 1 in it.

 

[wonderbread23]

Always calibrate your equipment. My hydrometer is +4 pts. high, so I always subtract 4 from the reading.

 

[Naked_Eskimo]

How do you calibrate your hydro?

 

[motobrewer]

put it in distilled water at 68F. If it reads 2 points higher than 1.000, always subtract 2 points from your readings.

 

[robbyg]

Thanks for the information, folks. After this morning's tap water reading, I suspect my hydrometer is also 4 points high (my tap water is quite good, so I doubt I have too much in in there contributing to the SG). But perhaps tonight I'll boil a water sample, cool it and test again just to be 100% sure.

If my hydrometer does read high, that means my original and current gravity readings are only .001 off the estimate. I think I'm comfortable with that. This is a 2 gallon batch, so I'm guessing a cup or two water variance in my wort could make .001 difference in a gravity reading.

 

[motobrewer]

i'm sure your tap water is fine.

i wouldn't get too hung up on gravity readings unless you're chasing a big efficiency problem. especially a point or two.

 

[MrWiggles]

Yep, I found out mine read 1.002 on tap water when I first bought it. I've just been subtracting 2pts from every reading I took and things have come out fine so far. Although I havent tried tapping that paper down to level it, thanks for the tip!

 

[carnevoodoo]

put it in distilled water at 68F. If it reads 2 points higher than 1.000, always subtract 2 points from your readings.

Remember that not all hydrometers are set to 68. Mine is calibrated for 60.

 

[JLem]

But perhaps tonight I'll boil a water sample, cool it and test again just to be 100% sure.

BTW boiling your water won't really help any - anything in the water will remain in the water. boiled water does not equal distilled water.

 

[robbyg]

Thanks for the tip, JLem. I won't waste my time, then.

Would it then be safe to assume that, if my reading is 4 points high on 68F tap water, it would also be 4 points high on 68F wort brewed with that tap water?

(Also, my hydrometer is theoretically calibrated for 60F, but I've been adding a point as per their conversion chart to compensate for my water/wort temperature.)

 

[JLem]

not sure that it is linear. I would check the reading of distilled water, adjust according to the temperature correction chart and then see where it is - noting if and how much it deviates from 1.000. Then, you would take the gravity of your wort, adjust according to the temperature correction chart and then correct for any baseline hydrometer deviation.

 

[JVD_X]

put it in distilled water at 68F.

or 60 degrees, depending on the calibration listed on the hydrometer.

 

[robbyg]

I tested my hydrometer this evening with 60F distilled water... it came in at 1.004. So now I know to simply adjust my readings accordingly. Thanks for all the help!

 

[Hex23]

I realized about three weeks ago that mine is 4 pts too high and I was bummed about my OG's not being as high as I thought. Ever since then I started wondering if that's what's happening when some posters get worried about their FG being too high.

 

[XPLSV]

And old thread, but... I have ran through my first several batches of brew and have consistently had high SG readings. My first batch was an extract and I didn't do much more than record the readings. The second batch was all grain and I thought we screwed it up. Batches 3 and 4 went more according to plan (aside from the fire on Batch 3) and I began questioning my hydrometer at that point. After kegging Batch 3 the other day with a FG reading of 1.029, I went out and bought some distilled water at Walmart (oddly, the first Walmart was sold out of the stuff). My distilled water reading at room temp was 1.020. Kind of a big "doh!" reaction at that point. Guess the paper slipped in that one quite a bit before it ever came into my hands...