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I normally use 10# pounds of grain in a 7.5 gallon boil, and normally hit between 1.045 and 1.055 OG, after it evaporates down to 6+ gallons, depending on the amount of dark grains used. My stove setup cannot boil much more than 7.5 gallons.

If I were to add, say, 5# of grain but keep my water constant, should I expect a roughly 33% increase in my original gravity? Or, can water only hold so many sugars before it becomes saturated, and the only solution is to increase my boil volume?

If the latter is true, what is the theoretical maximum OG of preboil wort for a given amount of water?

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There is a max threshold for how much malt derived sugar will dissolve in water, but that' isn't the factor to be concerned with as its much higher than what you'd get with malt alone.

The thing to worry about is that with less water you extract less from the grains themselves. Not a conversion or solubility issue, but a rinsing/extraction issue. As the the brewing liquor's sugar concentration goes up an ever lower gradient exists between the sugars trapped in the grist material and the water itself. This makes it hard to get all the potential out.

Most mash setups average 70-75% efficiency of getting the sugars out. Decreasing grain does not improve efficiency, despite the fact that this increases the water to grain ratio in your example. At a normal gravity like 1.060 and below, you'll only see the gravity drop. If you per se, were doing something like a 1.090 wort then maybe it would improve some to have more water to grain. Think of it this way. If your mash/lauter was 75% efficient, would dropping the grain by 33% give you 108% efficiency.

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Very high gravities of Wort (malt water) can be achieved in a mash (never "boil" grains). Super high if a reiterated mash process is used. So sugars in wort isn't a concern for your system.

Your mash should have a water grain ratio of 1.25 quarts per pound of grain. For a good balance of protein / sugar extraction. There is a much larger range of ratios that can be used, but for simplicity this is the usual ratio.

That being said for a 7.5 gallon pot your grain limit is 19lb. But that's to the very top.

15lb grain in a 7.5g mash tun is easily do able.

Welcome to high gravity beers!

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