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Spiciness is measured in Scoville Units. Basically:

In Scoville's method, an alcohol extract of the capsaicin oil from a measured amount of dried pepper is added incrementally to a solution of sugar in water until the "heat" is just detectable by a panel of (usually five) tasters; the degree of dilution gives its measure on the Scoville scale. Thus a sweet pepper or a bell pepper, containing no capsaicin at all, has a Scoville rating of zero, meaning no heat detectable. The hottest chilis, such as habaneros and nagas, have a rating of 200,000 or more, indicating that their extract must be diluted over 200,000 times before the capsaicin presence is undetectable. The greatest weakness of the Scoville Organoleptic Test is its imprecision, because it relies on human subjectivity. Tasters taste only one sample per session.one sample per session.

I'm making a chili beer, and while I have an idea of what I want to do, I thought some math could come in handy. How would you take the Scoville units of, say, a habanero (200,000 units), and the volume of a batch (5 gallons), and figure out how much habanero to add to get the final beer to, say, 75,000 Scoville units?

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Interesting. Also, I'd be interested if a brewer has ever determined the Scoville rating of their pepper brew. Additionally, is there a way to quantify spiciness chemically, given a sample? –  Taylor Oct 26 '10 at 22:19
    
This is from my friend James, who isn't on this site: I don't think that is solvable, there is some info missing. You need to know how much of the pepper was used to determine the rating. If you know that then you should be able to use a simple ratio or dilution equation. Something like Conc1*Volume1=Conc2*Volume2 or, if you remember gen chem, (M1V1=M2V2) –  hookedonwinter Oct 26 '10 at 22:40
    
This is from my friend who isn't on this site: I don't think that is solvable, there is some info missing. You need to know how much of the pepper was used to determine the rating. If you know that then you should be able to use a simple ratio or dilution equation. Something like Conc1*Volume1=Conc2*Volume2 or, if you remember gen chem, (M1V1=M2V2) –  hookedonwinter Oct 26 '10 at 22:40
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This is from my friend who isn't on this site: I don't think that is solvable, there is some info missing. You need to know how much of the pepper was used to determine the rating. If you know that then you should be able to use a simple ratio or dilution equation. Something like Conc1*Volume1=Conc2*Volume2 or, if you remember gen chem, (M1V1=M2V2) –  hookedonwinter Oct 26 '10 at 22:41
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@Taylor - I've read that now most scientists have abandoned the Scoville method for High Performance Liquid Chromatography, which can actually measure the amount of capsaicin in a solution and is much more accurate. –  Room3 Oct 27 '10 at 12:50
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1 Answer

According to this professor at UNC, they make the extract with one pepper. For the calculation I'll assume that your beer can extract capsaicin from the pepper you use as efficiently as the lab extract (which is most likely not true, but it gives you a base to start from).

This calculation is just a shot in the dark, but it makes sense to me:

First, 1 habanero (seeds and all) is approximately 1 teaspoon of ground habanero powder accourding to this spice company (we have to get a volume measurement before we do anything), so I will assume that 1 teaspoon of powder is about equal to the actual pepper on the Scoville scale (200,000 in your case).

5 gallons of beer is 3,840 teaspoons, so would dilute 1 habanero to about 196,160 Scoville units.

That way overshoots your target of 75,000, so lets try it with half a habanero (about 100,000 Scoville units).

5 gallons of beer is 7,680 half-teaspoons, so would dilute 1 habanero to about 92,320 Scoville units. This gets pretty close to your target of 75,000, and since the heat of your exact pepper is unknown, I would say it's a pretty good approximation.

Maybe that 92,320 will get down in the 70,000-80,000 target range when you account for the capsaicin that you can't extract.

I'm, not sure how you were planning on incorporating it, but I would slice it half-wise vertically to accurately get half of the pepper, then crush the half you want to use with a mortar and pestle and stir the habanero paste in.

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This is great, thank you! Though I can't imagine 1 habanero would make the beer as spicy as eating a habanero straight (196,100 is pretty close to 200,000). –  hookedonwinter Oct 27 '10 at 15:54
    
Is Scoville rating the dilution required in total volume, or sugar, or both? If it's just capsaicin per volume, I think Room3's calculation would be correct at 196k. However, I think it's capsaicin per sugar per volume. Of course, as Room3 pointed out, the scale is hardly accurate anyway. @PJ take a sample of the brew to a chem lab (maybe DU's) and see if you can have the capsaicin isolated and measured :) –  Taylor Oct 27 '10 at 16:15
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