Quick question about volume markings and temperature

[Mothman]

I am about 99% sure this must have been asked before, maybe many times, but my searching has failed me on this specific question.

I'm about to go through the process of marking volume increments for my 9 gallon pot, for now going to mark half gallons on my stir spoon.

I've found that a cheap plastic half gallon juice container we own is pretty much bang on when I measure cold tap water by weight.

I was all set to measure out with increments with that cold tap water. from that jug, but now have my head all twisted around, unsure if I should be marking the paddle with the water cold, room temperature, near boiling....?

Probably RDWHAHB applies, but figure I might as well do it in a way that follows general consensus.

 

[IndyBlueprints]

My understanding is there is about a 4% shrinkage when cooled. Can you really see a 4% difference in a gallon of water?

I'd measure at room temperature. That's where your beer will start and finish.

 

[Frodo]

The main thing is that you know at which temp you marked it. 4% gets to be around 1/4 gallon at 7 gallons, which for me is enough to matter for figuring efficiency and post-boil vol. I have a stick I marked when the water was cold, but I always have to remember that it's about 1/4 gallon off at boiling temp when it's around 7 gallons (I should mark off a new stick at boiling temp!).

 

[Mothman]

Sounds good. I guess the main thing is knowing what I actually measured and adjust as needed.

If I was aiming for, say, a 6 gal preboil volume, and my spoon was marked at room temperature, I'd be good if I was just a smidge over my 6 gal mark, correct? (Or just go for the 6 gal mark and call it close enough)

Edit - frodo answered as I was posting. Thanks guys, makes sense.

 

[Frodo]

About a quarter of the way toward the 7 mark. (at boiling)

 

[GPP33]

Home Depot sells an aluminum yard stick. Already marked, easy to figure out partial gallons and easy to calculate depth at different temps.

 

[Mothman]

I've considered the yard/meter stick approach. May still do it that way if I find my pot truly does scale up consistently.

 

[TomVA]

A gallon is a gallon, a unit of volume, and it doesn't change with temperature. What changes with temperature is the weight of a gallon. If you are calibrating your spoon with room temperature water (70°F) you would weigh out 8 lbs and 5.2 ounces of water per gallon (or 4 lbs, 2.6 ounces per half gallon). If you calibrated with hot water (120°F) you would weigh out 8 lbs and 4.0 ounces of water per gallon (or 4 lbs, 2.0 ounces per half gallon).

Best to calibrate at room temperature as it is safer and doesn't change while you are calibrating. I have calibrated my S/S pots at half gallon increments with a S/S ruler measured to the nearest 1/16 inch, which for my 8 gal pot equals 0.038 gallons. For my plastic fermenting pails I shine a flashlight into the pail to see the water line and mark the outside of the pails with a sharpie.

BTW, the preprinted volume marks on my fermenting pails were pretty far off.

TomVA

 

[kh54s10]

I marked my dip stick with tap water during the summer, so pretty much room temperature. I then worked out my boil off rates and know that I need a little over 7 gallons preboil to end up with a little over 5 gallons into the fermenter. I don't really care what the scale is at different temperatures as long as I get the right amount into the fermenter.

 

[Puddlethumper]

I have an aluminum dip-stick that I marked at 1/2 gal. increments with an engraving tool. I've used it for years and it works just fine. Just keep in mind that if your post-boil volume is off by a bit there is no crime in adding a quart or two of reserved strike water to get the fermenter volume up to where you want it.