Pre Boil Gravity Question

[bignath]

Hi all,

it's getting late, i've had a few, and am halfway through a double brew session. Just a quick question.

Whilst measuring my pre boil gravity, i measured 9.4 brix (1.036) points coming straight out of the mash tun. (Actually put the pipette for refractometer into stream as it goes into kettle.)

Then measured the gravity of the collected wort in the kettle and got 10.0 brix (1.038) actually in the kettle.

This may seem like a stupid question, but which one is the correct pre-boil gravity? The mass of collected wort, or the presumably dropping gravity of the mash runnings?

Cheers,

bignath

 

[Hatchy]

This sounds familiar, I've had a couple of batches where my pre boil gravity is lower than the last dribbles of runnings into the kettle. My (cheap ebay $30) refractometer gives accurate readings post boil into the fermenter measured against my hydrometer (which I assume is accurate). I've had to do 2 batch sparges a few times & my pre boil gravity has been lower than my 3rd runnings each time. To answer yr question, I don't know. I'm glad it's not just me though.

I'm also glad to hear I'm not the only one who brews at 2am. I hope yours turns out better than mine did.

 

[bignath]

This sounds familiar, I've had a couple of batches where my pre boil gravity is lower than the last dribbles of runnings into the kettle. My (cheap ebay $30) refractometer gives accurate readings post boil into the fermenter measured against my hydrometer (which I assume is accurate). I've had to do 2 batch sparges a few times & my pre boil gravity has been lower than my 3rd runnings each time. To answer yr question, I don't know. I'm glad it's not just me though.

I'm also glad to hear I'm not the only one who brews at 2am. I hope yours turns out better than mine did.

Thanks Hatchy, yeah brewing into the wee hours of the morning. Two rugrats, busy work, gotta fit it in somewhere.

My estimated pre boil gravity for this recipe is 1.035 so either way i'm pretty damn close. Was wondering what most people used for the "pre boil" readings. Not too fussed, i'm close enough to keep me happy with my estiated pre boil.

I'm doing a nelson sauvin smash (read: knappstein clone). In the brewing shed, playing darts, drinking tony's LCBA recipe. Life doesn't get much better surely?

EDIT: would love to get into contact with some AG brewers in the south east. Speaking to my LHBS guy, i don't know that there is many others. He told me there was no way to filter beer besides CC'ing and finings (obviously never heard of filters etc...) makes me think that at least he doesn't get much business from like minded people. K&K probably a different story.....

cheers bignath

 

[Thirsty Boy]

Your last running gravity has nothing to do with your pre-boil gravity. You want to measure the gravity of the mass of wort in the kettle. And you want to make sure it's well mixed before you do to. I wait till the kettle has come to the boil and boiled for a minute... That mixes it properly. Then take a pre-boil. Or stir it really thoroughly if you don't want to wait.

Hatchy... You third runnings "could" be higher than your pre-boil (some guesses)

A} because you didn't stir your kettle well enough and you have less dense wort floating on top of teakettle where you took your sample from

B} because in that third runnings, you are extracting a bit of tannins, those count as extract too, and when gravity drop low enough from sagging, it starts to rise again as tannins etc start to be pulled out of the mash. This is a fly sparge issue mainly though, so probably not yours.

C} despite things written about refractometers not needing to adjust for temperature... I still find I get a moremreliable reading from mine if I cool the wort down before i put it on teh refractometer. Some people just dip the damn thing in the ketttle. Mine doesn't even come close to accurate if I do that sort of shit.

I mainly guess mixing. How was the gravity once you finished your boil? Did all the numbers add up gravity points wise?

 

[speedie]

TB why do you take readings pre boil

Can only guess that it is to correct gravity for batch

The only thing I do during runoff is sample the stuff

It should be a breakfast drink, liquid bread
cheers speedie

 

[JestersDarts]

... In the brewing shed, playing darts, drinking tony's LCBA recipe. Life doesn't get much better surely?

three out of three things I want to be donig right now.

 

[argon]

TB why do you take readings pre boil

Can only guess that it is to correct gravity for batch

The only thing I do during runoff is sample the stuff

It should be a breakfast drink, liquid bread
cheers speedie

after the 92% efficiency thread... then this comment... that blows my mind!!!! :blink:

 

[Thirsty Boy]

TB why do you take readings pre boil

Can only guess that it is to correct gravity for batch

The only thing I do during runoff is sample the stuff

It should be a breakfast drink, liquid bread
cheers speedie

Exactly - to ensure that things went the way I expected them to. My pre-boil volume is a constant, so I sample at that volume to make sure my gravity is as expected. If not, I can choose between accepting it as it is, adding cut water or DME to adjust gravity & re-adjust hop additions to maintain BU:Gravity ratios.

After lautering is complete I measure pre-boil gravity & volume, last runnings gravity & pH, post boil gravity & volume - and volume of uncollectable trub. These are the critical control points in my post mash brewing process, they are measured every time.

 

[manticle]

I don't usually measure pre boil gravity anymore but if I changed my processes or started using a new system and my efficiency wildly changed (or it just wildy changed), I would measure at every step to work out which bit needed tweaking.

A common question among new AG brewer is "my efficiency is terrible - how do I fix it?" It's hard to know how to fix it unless you know which stage of your process is contributing to the inefficiency.

 

[Spork]

my efficiency is terrible - how do I fix it?

Seriously, it just keeps getting worse. Doesn't seem to matter what I change. Under %60 today (%57) and last batch was only about %51.

I've tried crushing really fine - didn't help.

Happy with the crush I get now, many grains still "look" intact, but crumble easilly between my fingers, so they are cracked.

I did try dunk sparging on a couple of brews, for very minor gains in eff.

Today I even tried a different, larger mesh bag. It drained nice and fast, but no better eff.

I'm starting to think it's the JW ale malt I use as my base. I did several brews with a sack of MO and seemed to get consistently higher eff. using that. Anyone had any problems with JW ale malt? Or should I be looking elsewhere? (Although I really haven't changed anything between my first few brews (eff. in low - mid 70's) and now (high 50's - low 60's)

 

[sim]

um as per above, i dont think people can help you unless you give some measurements - pre and post volumes, pre and post gravities, dead space in mash-tun, loss to trub.

This efficiency of yours - is that mash efficiency or brewhouse efficiency?

I cant comment on BIAB. I dont have a problem with JW malts.

 

[Spork]

OK, sorry about my vagueness in previous post, was sort of tongue in cheek, but I really am finding it a problem.
Thats my brewhouse efficiency, according to brewmate. Losses to trub etc. have not changed.
I BIAB. Typically I start with 31 - 33 litres of strike water (depending on size of grain bill) and my pre-boil gravity just seems to get lower and lower.
Today for example, I started with 33 litres water @ 70.3c and 7.2 kg grain. Mashed @ 67c for one hour. Raised bag off element and heated to 72c, then turned heat off and dunked bag and gave it another good mash with paint mixer. Hoisted bag and let it drain.
Pre boil I had about 29 litres of 1.051 wort. It "Should" (with eff. set to %63 in brewmate) 28.8 @ 1.058. I'm getting the "right" volumes, but the gravity is too low. Post boil I still had pretty much the volume that BM estimated, but gravity remained low (1.056).

The grain bill was:
6kg trad ale malt
.4 kg caramunic
.4kg munich 1
.4 kg wheat malt.

Thats not too much spec:base malt is it?

I'm not %100 sure of my strike / mash temps either, as no 2 thermometers I own seem to agree %100 with each other. It could be +/- 1c... but would that make such a big difference to OG? I thought it would affect FG more, and most my beers are finishing between 1.008 and 1.013...

fkn...

advice? Any other details needed? Cheers.

 

[bignath]

what sort of gap have you got your mill set to?

I know in your previous post you said you were happy with the crush, but it may shed some light to know how big or small the gap is. Do you have a set of feeler guages?

 

[MHB]

There two obvious places to look
Your malt - dont blame the maltster, have a look at storage and age, order some fresh malt from a trusted source and see what happens.
Your thermometer if its drifting you would have no idea what temperature you are really mashing at, you should have 1 good quality glass laboratory thermometer you can use as a reference. At $10-15 they really are a necessity.
Mark

 

[Spork]

Thanks Big Nath.
Got some old feeler guages - imperial sizes, and too rusty / discoloured to be able to read the numbers stamped on them properly. Mill gap is "a credit card" wide.
Might have to grab a new set of feeler guages. But - have adjusted mill gap, did a couple of brews with more flour than husks (very small gap), and eff. was very low with the finer crush too.

MBH - Fresh bag of mal (base)t. Opened and brewed on the same day for my lowest eff. ever... The spec. malts are < 6 months old, and have been stored dry in small wheelie - bins in the spare lounge (much to my wife's disgust...) They still smell and taste fresh. I might try a single malt batch with the fresh sack though to see if that helps.
I bought a "proper" glass thermometer from my LHBS ($30!). And it's probably less accurate than my $5 ebay digital one or the probe on mt STC 1000... I know it's inaccurate because it shows boiling water as only being 92c... The other 2 ($5 ebay and STC) are within about .5c of each other.
Might just bite the bullet and buy (yet another) thermometer. Can you link me to a site with $10-15 ones, that are accurate, esp. @ strike and mash temps?

Thanks for the advice guys.

 

[potof4x]

Spork I run on very soft tank water and found adding some calcium to the mash helped my efficiency, I also add my yeast nutrient to the mash now too, i think i read something by mhb (sorry if it wasn't ) about helping with the mash enzymes. Gross simplification of water chemistry by me, but it is working.
Also when using brewmate pay attention to what u set your 'loss to trub' to, as increasing this figure does not affect your predicted preboil gravity, even though there will be more water in the kettle.

 

[robbie_d]

Not that I have done this a lot of times, but are you putting 'the bag' in the mash tun open and stirring the grain in as you add it, or all wrapped up 'pudding style'.
It sounds like there isn't enough grain-water interaction happening. Also with that amount of grain (it was pointed out to me this week) that it will reduce the water temperature as you add it.