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General Category => All Grain Brewing => Topic started by: nofunsally on May 09, 2011, 05:44:58 PM

Title: Measuring gravity to inform when to stop mashing
Post by: nofunsally on May 09, 2011, 05:44:58 PM
Hello,
I recently acquired a refractometer. I've been told its great to check the gravity of the wort in the mash and also to know when to stop collecting wort.  Could some one please tell me about checking the gravity pre-boil / mash or point me to the literature? 

I typically get about 75% efficiency into the fermentor from my brews. I use a 48 qt rectangular cooler with a stainless steel braid.

I don't know what to search for to find this information.

Thanks,
Mike
Title: Re: Measuring gravity to inform when to stop mashing
Post by: nateo on May 09, 2011, 06:04:23 PM
The most common number I've seen is 1.010, meaning stop sparging once your runnings drop below 1.010 SG.
Title: Re: Measuring gravity to inform when to stop mashing
Post by: narvin on May 09, 2011, 06:07:50 PM
Kai has some good info on mash efficiency here:

http://braukaiser.com/wiki/index.php/Troubleshooting_Brewhouse_Efficiency
Title: Re: Measuring gravity to inform when to stop mashing
Post by: tomsawyer on May 09, 2011, 06:21:09 PM
When I try a new mashing routine I'll check my mash every fifteen minutes and let it go until the Brix quits rising.  This way I know I've got complete conversion or at least as much as I'm going to get.

As for checking during fly sparging, you just check every so often and stop when the sugar content gets low, or you've reached your target volume.  Probably every five minutes would be enough early on, assuming your sparge takes 30+ minutes.

Be sure to rinse off the refractometer each time and dry it with a soft cloth that won't scratch the surface of the glass.
Title: Re: Measuring gravity to inform when to stop mashing
Post by: nofunsally on May 09, 2011, 07:32:13 PM
Thank you all for the information.

Maybe this will lead to more predictable results for me.

Cheers,
Mike
Title: Re: Measuring gravity to inform when to stop mashing
Post by: weazletoe on May 10, 2011, 03:21:56 AM
And, if you have a program like Promash, or do a little simple math, which I do not recall right now (I'm sure someone can help me out here) You can take a preboil gravity, and volume, and see just how long you need to boil to reach your target gravity. or, if your efficency was extra high that brew day, add some water to thin it out. Do this, and you can hit your numbers spot on, every time.
Title: Re: Measuring gravity to inform when to stop mashing
Post by: sharg54 on May 17, 2011, 07:12:51 AM
Pre-boil gravity times gallons of wort before boil divided by target gallons after boil is the formula you want.  In others words  a 1.035 pre boil wort of 7 gallons and a target of 5 gallons works like this.
 ( 35 x 7 ) / 5 = 1.049 OG at end of boil.
It works very well just don't forget to adjust your reading on you hydrometer for the temp your checking it at.   
Title: Re: Measuring gravity to inform when to stop mashing
Post by: punatic on May 17, 2011, 07:33:16 AM
You can use a parrot:

(http://www.homedistiller.org/graphics/measure2.jpg)
Title: Re: Measuring gravity to inform when to stop mashing
Post by: sharg54 on May 17, 2011, 07:36:24 AM
Quote
You can use a parrot:

Now thats a fun looking toy... lol.
Will that drop the temp to 60 degrees where most hydros are calibrated at or will it just stay at room temp?
Title: Re: Measuring gravity to inform when to stop mashing
Post by: punatic on May 17, 2011, 07:45:40 AM
Quote
You can use a parrot:

Now thats a fun looking toy... lol.
Will that drop the temp to 60 degrees where most hydros are calibrated at or will it just stay at room temp?

The upstream tube is existing a copper liebig condenser.  

Applied to mash runoff - you need to make temperature corrections.

This is an instantaneous way to monitor specific gravity.
Title: Re: Measuring gravity to inform when to stop mashing
Post by: ccarlson on May 17, 2011, 01:10:15 PM
You can use a parrot:

(http://www.homedistiller.org/graphics/measure2.jpg)

I was going to say that didn't look like anything related to brewing beer, then I saw the image file location. :D
Title: Re: Measuring gravity to inform when to stop mashing
Post by: punatic on May 17, 2011, 02:42:54 PM
It is a simple idea that can be used to monitor runoff gravity if you only have a hydrometer. 
Title: Re: Measuring gravity to inform when to stop mashing
Post by: denny on May 17, 2011, 03:28:29 PM
Quote
You can use a parrot:

Now thats a fun looking toy... lol.
Will that drop the temp to 60 degrees where most hydros are calibrated at or will it just stay at room temp?

I put a gravity sample in a metal cocktail shaker and put that in a bowl of ice water.  In just a minute or so, it's down to 60F.
Title: Re: Measuring gravity to inform when to stop mashing
Post by: jeffy on May 17, 2011, 04:46:00 PM
I saw the following invention by a homebrewer once: he glued a hydrometer flask into a plastic bowl (I think it was a spreadable margarine tub), filled the bowl with water and stuck it into the freezer.  I thought that was pretty clever.
Title: Re: Measuring gravity to inform when to stop mashing
Post by: ccarlson on May 17, 2011, 04:54:23 PM
One word: Refractometer