Where does my gravity go?

guypettigrew · Post by **guypettigrew** » Sun May 06, 2012 7:02 pm

My gravity always drops after boiling. Here's the scenario. Apologies for Imperial measures, but I drink in pints, so I brew in gallons!

Today I brewed a straightforward bitter.

Pale malt, pale crystal malt, Fuggles and Goldings hops. White Labs 002 yeast (Fuller's ESB).

After sparging I collected 5 1/2 gallons at a gravity of 1.050. My calculation is that this would become 1.055 once reduced to 5 gallons. (50 x 5.5) / 5 is the calculation I used. Perhaps this is fundamentally wrong?

Having boiled the wort, which reduced to about 4 1/4 gallons, then topped up to 5 gallons, it read 1.050.

So, where did the other 5 degrees of gravity go? This always happens.

Guy

gnutz2 · Post by **gnutz2** » Sun May 06, 2012 7:13 pm

Gravity will go up as liquid evaporates, are you correcting your hydrometer reading for temperature?

guypettigrew · Post by **guypettigrew** » Sun May 06, 2012 7:24 pm

Yup, I use a refractometer.

Guy

gnutz2 · Post by **gnutz2** » Sun May 06, 2012 7:43 pm

Well i'm baffled.

Try giving the wort a real good stir before you take the OG reading, i once left 5 gallons of wort overnight in the boiler and took a hydro reading from the top which ended up way down on gravity. Once i gave the wort a good stir it must have mixed the sugars up and the reading was back to normal.

Cheers Baz

Andy__ · Post by **Andy__** » Mon May 07, 2012 2:06 am

The hops you use in the boil will absorb some of the wort and with it some of the sugars

BrotherLogic · Post by **BrotherLogic** » Mon May 07, 2012 10:49 am

Did you calibrate your refractometer? Otherwise something weird is going on, or you're measuring wrong

super_simian · Post by **super_simian** » Mon May 07, 2012 11:44 am

Losses to trub and hops?

BeerEagle · Post by **BeerEagle** » Mon May 07, 2012 11:52 am

Surely anything left in the hops/trub etc will be at the same concentration as the wort. They won't suck sugars out of the wort.

I suggest you take another gravity reading after the boil and before you dilute, then you can find out at which stage it's getting weird.

schlafsack · Post by **schlafsack** » Mon May 07, 2012 11:56 am

Do you use an immersion chiller and has it got a leak? You could be accidentally diluting you wort.

worldsbestbrewer · Post by **worldsbestbrewer** » Mon May 07, 2012 12:37 pm

Are you taking into account that your wort will 'shrink' by about 4-5 pcent in volume when it cools from 100C to 20C. Eg taking yr first readings and calculations on 'hot' volumes and then topping up when 'cold'., so actually having to add 4-5 pcent more water as it's now shrunk. Not sure iof i have that the correct way around, but food for thought:-)

G

guypettigrew · Post by **guypettigrew** » Tue May 08, 2012 12:58 pm

Thanks for all the ideas.

My guess is it's the wort which is left in the hops after draining the boiler off. I always end up with 4 1/2 gallons in the FV after the boil, which I dilute to 5 gallons.

I need to check the gravity of the wort before topping up to 5 gallons, don't I? On the assumption there's no gravity loss at this point I'll have to think of a way of recovering all the wort from the hop bed. Or perhaps this can't be done?

At the moment, though, I'm getting about 85% efficiency after the mash, dropping to about 80% once the beer's back to 5 gallons in the FV---Beer engine figures.

Guy

weiht · Post by **weiht** » Tue May 08, 2012 2:23 pm

I guess the qns to ask is how much is left in the kettle, not how much goes into the FV... I'm pretty sure u are hitting ur numbers quite right, probably just 2%+/- off. Do a gravity check before running off into the FV, and find out how much wort is in the kettle left.

There will definitely be losses somewhere in the brewhouse after mashing, ie to the trub, hops and even if u are using pellet or flower. That is why mash eff. is different to brewhouse eff. in beersmith. One way to work around it is to brew slightly more.

I keg (19L), but i brew 23L because I lose about 2L to the trub and hops, and am prepared to lose another 1-2L in the FV (Hydrometer samples etc).

Kev888 · Post by **Kev888** » Tue May 08, 2012 4:49 pm

guypettigrew wrote:I always end up with 4 1/2 gallons in the FV after the boil, which I dilute to 5 gallons.

That sounds like it to me - unless you're measuring wrongly then the gravity is not reducing during the boil, its reducing when you dilute the wort; measure it before topping up and you'll be able to verify that.

Its not so much that the hops are leeching sugars from your wort, its just that wort is being retained which you are replacing with water. If you include the losses in your brew-length calculations (and so brew a bit more accordingly) there should be no need to top up (unless your boiler is too small or something). Personally my pre-boil volume is enough to compensate for evaporation, losses to boiler dead space, losses to hops and losses to FV deadspace, so that theres enough after fermentation to fill my kegs.

BTW, depending on your boiler design, the hops may just lurk in the existing boiler deadspace - if so then they don't steal any more wort than the dead space would without them.

Cheers
Kev

worldsbestbrewer · Post by **worldsbestbrewer** » Wed May 09, 2012 10:59 am

Well, hops are dried and someone like Tony will tell you exactly how much wort they will retain, which is quite a lot. Like Weiht my brew length is 50l to collect 2 cornies and maybe a bit for a jug or bottle. As I'm not commercial i'm not bothered about a few litres wastage as it's literally pennies and part of the process.

Kev888 · Post by **Kev888** » Wed May 09, 2012 11:26 am

worldsbestbrewer wrote:Well, hops are dried and someone like Tony will tell you exactly how much wort they will retain, which is quite a lot.

Its not a completely predictable amount betyween different systems etc, but for whole hops I reckon on them retaining roughly around 1.5L per 100g if you have a free draining boiler (unless you squeeze them or wait 'ages' for the last dreggs). If you need to maintain a syphon effect or if you pump out it can be greater though, as air can start to get drawn off as you try to suck out the dreggs - for example with a pump mine rises to about 1.9L per 100g.

However many people's boilers have some deadspace anyway, which the hops sit in; in that case the wort they retain is partially or wholly shared with the deadspace losses, rather than being simply an addition to it. So as an extreme case then if your deadspace was greater than the space occupied by your hops and trub they will not retain any additional wort.

Either way though, the hops themselves will not cause the gravity to drop to anything like this degree, they mainly just reduce the final brew length by retaining wort and its the subsequent topping up (and so the dilution of the sugary wort) that is causing the gravity to drop.

Cheers
Kev

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