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Home Brew Forums > Home Brewing Beer > Equipment/Sanitation > New (larger) brewkettle contributing to lower OGs?
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Old 01-05-2013, 01:36 PM   #11
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That is supposed to say, "multiply that by your initial volume," not "by your initial gravity."

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Old 01-06-2013, 06:03 PM   #12
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I did a few calculations using the formula that cluckk suggested...
Suppose I start with 6 gallons of wort, pre-boil, at 1.050. If I boil down to various volumes, here's what I would be looking at *before* I top off to 5.5 gallons in my carboy:

Boiled down to...
5.5 - 1.055
5 - 1.060
4.5 - 1.067
4 - 1.075

If I plan to top all of these off to 5.5 gallons for primary fermentation, I would need to add various amounts of water to do this. The results are interesting...

5.5 (no extra water needed) - 1.055 OG
5.0 (.5 gallon added) - 1.055 OG
4.5 (1 gallon added) - 1.055 OG
4.0 (1.5 gallons added) - 1.055 OG

What this suggests to me is that it doesn't matter how much you boil, as the volume is restored to a full 5.5 gallons for primary fermentation anyway. The amount of sugar hasn't changed, and neither (in the end) has the water. So I'm still confused on how boil-volume affects the OG.

As for my other concern , in reading some other comments, perhaps I'm not aerating my wort well enough. I'm still able-bodied enough (and cheap enough) to be content rocking my carboy back and forth for my aeration. I have a number of other methods used in other threads, including research abstracts on the matter, and many suggest that rocking is sufficient if done for only 5 minutes. Maybe I just need to do this for longer...?

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Old 01-09-2013, 07:02 PM   #13
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Quote:
Originally Posted by saxman1036 View Post

The amount of sugar hasn't changed, and neither (in the end) has the water. So I'm still confused on how boil-volume affects the OG.
OG is the gravity of your wort going into the fermenter. Changes through boiling and topping off are what gets you to that OG. What you are measuring is the amount of sugar dissolved in a volume of water. If you change either the water or the amount of sugar you change the gravity. Boiling does many things--sanitizing, blowing off unwanted compounds, isomerizing hops, etc. With gravity, boiling changes the ratio of water to sugar. To raise final gravity you can either increase the amount of sugar through mash efficiency or reduce the amount of water by boiling down. For example:

If I brew a batch in which I want an OG of 1.050 in a 5.5 gallon batch, and I start with boiling 7 gallons from my MLT, then I need my preboil gravity to be 1.039. However, what if I miss this number way low? If my efficiency is off in my mash and I only get 1.025 in that 7 gallons then with the same amount of boiling I will only achieve an OG 1.031 (into fermenter). This will be a very weak beer and way off my target. However if I boil it down to 3.5 gallons my gravity of 1.050 is hit and I would then cool and ferment this amount. I would end up with much less beer, but it would be at my gravity. (I would have traded volume for gravity) If I insist on having a 5.5 gallon batch then I must accept the weaker beer (unless I add sugar in one form or another).

Note: you would have to boil much longer which would caramelize more sugars (making it sweeter) and would also require you to alter your hop schedule.

The only other option, after pulling off from the MLT and starting the boil would be to add sugar into the kettle--such as Brewer's Sugar, honey, extract, etc. Be careful about these because they will thin out a beer.

I had one batch come in very low--it was during a parti-gyle experiment--so I added Brewer's sugar to the kettle and raised the OG from 1.023 to 1.030. This will of course produce a thinner beer, but I wanted the gravity.

The issue is the topping off. If your gravity is not high enough you can either remove water and have less of a stronger beer, add sugar to make the larger beer stronger, or continue to top off to get you target volume of a weaker beer.

If you have the kettle and MLT volume for a full batch and a cooker that will boil 7 to 8 gallons reasonably, then give up the topping off and instead boil the full batch.
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