Sight Glass vs. Buckets

I'm have a problem with differences in my kettle's sight glass versus my bucket markings to get the right amount of pre-boil volume.

The markings on my 6.5 gal brewing buckets are spot-on. I use these to collect wort during lautering and today I collected 3 gallons of first runnings and then two sparges of 2 gallons. So that's 7 gallons total and I've calibrated the markings on the buckets with warm water.

Now when I transfer to the kettle it reads 6 gallons but with changes in density with temperature and sugar content I never really thought it was wise to trust it.

But that sight glass is always right. If I lauter 7 gallons in the buckets it'll read 6 in the kettle sight glass. After the boil the sight glass reads 4 gallons and I end up with 4 gallons in the fermenter. My winter boil-off is about 2 gal/hr so if I had the 7 gallons lautered according to the bucket then I should have 5 gallons in the fermenter.

I'm just trying to figure out why my buckets and my sight glass can't agree and why the sight glass, of the two, has always been right...

Arrheinous said:

The markings on my 6.5 gal brewing buckets are spot-on. I use these to collect wort during lautering and today I collected 3 gallons of first runnings and then two sparges of 2 gallons. So that's 7 gallons total and I've calibrated the markings on the buckets with warm water.

Now when I transfer to the kettle it reads 6 gallons but with changes in density with temperature and sugar content I never really thought it was wise to trust it.

But that sight glass is always right.

Click to expand...

I'm just trying to figure out why my buckets and my sight glass can't agree and why the sight glass, of the two, has always been right...

Click to expand...

Click to expand...

I hate to point out the obvious, but they cannot both be correct. Some of this may be attributable to the cooling loss from boiling to room temperature, which I believe is 4% (that's what Beersmith lists for cooling loss); the boiling wort expands by 4% in volume. So, 6 gallons expands to 6.24 when boiled.

Yeah, one of them has to be wrong.

The 6 vs 7 gallon measure is happening after lautering when I transfer the "7" gallons of wort in the bucket to the kettle. All of the liquid in both cases is at ~130F and both the bucket and the sight glass were dialed in at 120F (hot tap water) with the same 1 gallon jug.

The sight glass is pretty spot on for strike water volume and for pre-boil / post-boil volumes from 120F to boiling. Whatever it says is what has ended up in the fermenter. If it reads 4 gallons right before chilling the wort at 200F then it'll be 4 gallons in the fermenter at 68F.

I think the changes in density with temperature and SG are negligible with the ratio of water above the sight glass to the size of the sight glass. Or maybe it's in just the right spot (at the 3.5 gallon line) to balance that out. The temperature in the glass will be lower than the kettle. I've never had any of the problems people might associate with sight glasses - it's a fine piece of equipment and it looks cool. :rockin:

I guess the solution is to reallly double check that bucket. Maybe by weight, got a weighing scale now.

Arrheinous said:

The markings on my 6.5 gal brewing buckets are spot-on. I use these to collect wort during lautering and today I collected 3 gallons of first runnings and then two sparges of 2 gallons. So that's 7 gallons total and I've calibrated the markings on the buckets with warm water.

Click to expand...

So let me get this straight. You mash, lauter, then run off 3.5 gallons into the kettle, as in you get 3.5 gallons per the sight glass. You then sparge twice with 2 gallons each time. Barring large absorption during sparging (which shouldn't be an issue), you should have 7.5 gallons, but read 6? And you measure each water addition with the bucket(s), which you believe to be correct. Do I have this right?

If so, what are your readings after each sparge? If not, what are you doing differently?