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I have a recipe in front of me that calls for 1 pound, 2.5 ounces crushed 75L crystal malt. My store only sells in increments of 20L (so in this case, I have 60L and 80L). How would I calculate how much 60L and 80L crystal malt I would need to make 1 pound, 2.5 ounces of 75L?

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Unfortunately, diluting crystal malts down to get a lower value doesn't translate into what you'd get if you had used the lower crystal in the first place. Good question though and I upvoted it. –  brewchez Feb 12 '13 at 22:22
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2 Answers

up vote 7 down vote accepted

Honestly, there's often more than 5ºL variation between batches of crystal by the same maltster, so I'd probably just buy the 80L and be done with it.

But, if you want to try to be more precise, the Morey equation for SRM (which is what most software uses) just assumes a linear proportional effect. So, you'd want 3 parts 80ºL to 1 part 60ºL.

In other words: 4.625oz 60ºL and 13.875oz 80ºL.

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Thank you for the insight. Can you explain how you came up with 3 parts 80L to 1 part 60L? –  Scott Feb 12 '13 at 4:54
By mixing 60/80L malt, the most change we can make is 20L, by using all 80L malt. We want 75L, which is 60+15L. By dividing the desired change by the total change, we get the proportion of 80L required = 15/20 = 3/4. So we use 3/4 80L and the remaining 1/4 60L. So, 3 parts 80L to 1 part 60L. –  mdma Feb 12 '13 at 12:11
+1 for: "so I'd probably just buy the 80L and be done with it." The difference in 75L crystal and 80L here will be miniscule, probably past the point of notice. –  Graham Feb 12 '13 at 13:34
To say what MDMA said slightly differently, the ratio between 60L and 80L is just a weighted average: (60*m + 80*n)/(m+n) = 75. If you do the algebra on that, it turns out that (m:n=3:1). –  MalFet Feb 12 '13 at 14:15
@brewchez, You should have downvoted (or better left a comment on) the question, not the answer, since the OP specifically asks how he can combine 60/80L malt. The answer is a perfect fit to the question: first it says that combining isn't necessary, and then cites Morey to back up the math if the OP wants to combine all the same. With 60/80L, the flavor difference is not so much that this approximation does no harm. –  mdma Feb 12 '13 at 22:30
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It doesn't really work that way. You can't proportion out a crystal malt and hope to get a different one.

You can play with math all you want with this. But if you put half a pound of C120 in a quart of water, you won't have the same color as one pound of C60.

And the flavor differences in the malts is pretty significant in that example too. Diluting down the raisin/dried fruit flavors of C80 or C120, don't get you to the light caramel flavors of C40 of C20. It just gives you diluted raisin/dried fruit flavors.

C75 is so close to C80, your best just doing a straight up sub.

Oh and before anyone asks, I've done these experiments before too.

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The real error is to assume that there's such a thing as "C75" or "C80", as you seem to here. There's not, of course, as there is as much or more variation of numerically equivalent crystals between malsters as there is within a given maltster's crystal range. The sole useful constant comparable across different malts is color as measured by spectral absorption (SRM, for example), which does actually scale quite proportionally for different kinds of crystal malts. As for everything else, these are idiosyncratic ingredients. That's just the nature of brewing. –  MalFet Feb 12 '13 at 23:29
I don't assume that. I have seen a crystal labelled as 75L. I fully understand how they are made, and where the #s come from and that its generally an average. You have missed my point is that the flavor profile of one type of crystal cannot be made up by using more or less of a different one. Plain and simple. Secondly, but less important, the color expectation doesn't scale either. –  brewchez Feb 13 '13 at 2:27
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