Broken Hydrometer?

[MattGuk]

So, this seems to be a recurrent problem for me, the last 3 batches I am getting almost equal pre and post boil gravities.
Just finished up brewing and pre boil gravity was 1.042 @ 31.5 litres, post boil is 1.044@ 26 litres.
In theory none of my beers are going to be above 4.6% which is annoying.
Anybody else ever had this?

[guypettigrew]

This is impossible! A pre boil gravity of 1.042 @ 31.5 L should give you close on 1.051 @ 26 L. Simple arithmetic.

A silly question, but are you taking all the readings at 20°C

Guy

[MattGuk]

Yep both took @20°c, I'm sorry, but I don't do " simple arithmetic ".

[MattGuk]

I was simply asking if anybody has had this issue, and if so would it be a broken Hydrometer?
I have not been doing this as long as yourself obviously, hence my asking, you telling me that is " simple arithmetic " is slightly unhelpful and comes across a little rude.
I know it's impossible, thought it might be a fault in my process, however after 3 batches of having the same issue I guess it's not

[guypettigrew]

Apologies--I didn't mean to be rude or unhelpful. I just meant to show you what SG you could expect, when starting with 31.5L @1.042. The way the maths works is:

Multiply the original volume (31.5) by the last two figures of the gravity (42). Then divide by the new volume (26). (31.5 x 42) / 26 = 50.88.

This is a calculation I picked up years ago from Dave Line's first book on home brewing, which was back in the mid 1970's. Perhaps not many people know about it.

The issue is unlikely to be caused by a broken hydrometer. I'm guessing you've already checked it in water to make sure it reads 1.000.

What is your brewing process? A quick run through the latter part of the process may give some clues. How long do you boil for, do you achieve a strong rolling boil, what weight of hops do you use?

Are you taking both the gravity readings from the boiler, or is the post boil reading from the fermenter? I'm just wondering if drop in volume is more to do with wort retention by the hops in the boiler than evaporation during the boil.

There will be a good reason why you're getting similar gravity readings pre and post boil. We just need to work out what it is!

Guy

[MattGuk]

Thanks for this helpful info.
I have checked the hydro and all checks out in water @20°c.
This last batch used a total of 90g hops, all were pellets and were in muslin bags.
The reading was taken post boil after whirlpool, coming out the chiller and into fermenter so I'm sure it must be mixed enough.
I'm totally stuck by this as I had the same issue in the last brew, only difference was that was a cream ale using only 25 grams of hops total.
Cheers

[MattGuk]

I should also mention that I boil for 60 mins, I carry out full volume mashing without a sparge on a brew monk Magnus. This is only something that has started to happen more recently which makes me wonder about my Hydrometer.
I broke my previous one but never had this issue, it only seems to be since replacing my Hydrometer.
Maybe just coincidence?

[guypettigrew]

Increasingly strange! It's hard to believe your hydrometer's broken, but it would be worth checking it out in a known concentration of a sugar solution.

If you dissolve 16 grams of ordinary white sugar in 100ml of water it should give you a reading of 1.060 at 20°C. Or thereabouts!

This will tell you if your hydrometer has somehow gone wrong.

Guy

[MattGuk]

Thanks very much, I will try that, if that checks out then I'm really scratching my head as to what this could be, I know no sparge is less efficient in general but why my pre and post boil gravity are near enough the same even though I'm boiling off over a gallon is odd.

[WalesAles]

Aaaaaaaw! There`s lovely to see you both kiss and make up!

WA

[Trefoyl]

That’s an interesting calculation, Guy! I will have to check that out next brew day. I think I got Dave Line’s book recently too, but haven’t read it.
I’m wondering if your problem is that the wort isn’t entirely mixed when you take your preboil gravity. Recently I’ve let it boil awhile before measuring but I also changed to a refractometer so only need to cool a very small amount.

[MattGuk]

I'm thinking of going down the refractometer route.
I just can't understand why this has been a problem only recently, nothing in my process has changed, like I say only since replacing my old Hydrometer.

[Trefoyl]

The only thing I regret about getting a refractometer is that I didn’t get one a long time ago With a small stainless bowl to chill samples in ice water a few seconds it’s so easy to check gravity multiple times from sparge to the end of the boil.

[Eric]

Thanks for this helpful info.
I have checked the hydro and all checks out in water @20°c.
This last batch used a total of 90g hops, all were pellets and were in muslin bags.
The reading was taken post boil after whirlpool, coming out the chiller and into fermenter so I'm sure it must be mixed enough.
I'm totally stuck by this as I had the same issue in the last brew, only difference was that was a cream ale using only 25 grams of hops total.
Cheers

It is difficult to imagine any hydrometer being defective over such a limited range. For a 60 minute boil, pre and post boil gravities of 1042 and 1044 are not altogether unrealistic and within expected reading error of the hydrometer the boil-off could be 5 to 7%. The reported boil-off is in excess of 15%, and while that isn't unrealistic either, could the 31.5 litres be by measurement in the boiler while post boil by makings in the FV?

[MattGuk]

Yes, the 31.5 is measure from the boiler markings, also so is the post boil @26 after the wort had cooler before transferring into the fermenter.