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I've got some mint in the yard (I think it's apple mint, as the leaves are very fuzzy and rounded) from which I'd like to make mint extract. No specific use in mind (except perhaps insect repellent), just a kind of home chemistry experiment.

I've read that there are basically two ways to do this. One involves boiling the leaves, condensing the steam, and separating the oil. But the simplest way seems to be to steep the leaves in 80-proof vodka for about a month.

I have some questions:

  1. Is there something special (chemistry-wise) about alcohol that makes it more effective than other substances for extracting the oil?
  2. How strong would this "mint extract" be? It seems to me like I'd end up with mint-flavored vodka. Would the result be drinkable straight?
  3. After doing this, could I then freeze the result to separate the oil from the vodka?
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Just wanted to clarify something from the answers below - oils WILL absorb into water, however it is an issue of time. In chemistry water is referred to as "the universal solvent." Most oils will readily absorb into alcohol, whereas it could take months to even get a small amount of absorption into water. –  Matthew Jul 24 '13 at 15:08

3 Answers 3

up vote 9 down vote accepted

Why Alcohol?

Alcohol is used for extracts because the flavor compounds (plant oils) you are trying to extract do not easily dissolve in water. Alcohol (typically bourbon or vodka) will do the trick. Make sure you use +80 proof because it also acts as a preservative.

Making Mint Extract

To make an extract, tear up or coarsely chop and bruise washed mint leaves into a measuring cup (you'll end up with about twice the volume of extract as you have leaves). Transfer the leaves to a glass container with a tight-fitting lid. Add about twice the alcohol (by volume) as you had leaves. Cover and shake.

The mint leave will tend to float to the top, but give it a chance. After a few days, they'll start to bog down with alcohol and sink. Shake it every few days or so. After a month, you'll have mint extract. Strain the leaves and store.

Adjusting the Strength of Your Extract

The longer you let the leaves steep, the stronger the extract will become until all the oils are essentially spent. You can sample the extract along the way until you get something to your liking. If you want something stronger, you can add fresh leaves to your strained extract and continue the process. There's a limit though; as the alcohol become saturated, you'll get diminishing returns by adding more leaves.

Freezing the extract will not congeal the oils for further separation. They're essentially dissolved in the alcohol (unlike water + oil) and the alcohol will not freeze. Extracts are typically too concentrated to drink straight. For all that effort, it's better just to crush a few leaves directly into a drink with whatever ingredients will make it a proper cocktail.

Boiled Leaves isn't Really Mint Extract

The boiling water method you mentioned above wont achieve the same results. Even if concentrated, the flavor compounds in extracts are typically somewhat volatile (which is why you add them near the end of cooking). You're basically making concentrated, flavored mint water… but it isn't really an extract. And without the alcohol acting as a preservative, you're mint water will have a somewhat limited shelf life. Even distilling the volatile oils by boiling and condensing into a liquid might get you pure mint oil, but that would likely need very specialized equipment.

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Thanks! Follow-up question, will the same method work for Lemon Balm? –  Kelsey Rider Jul 23 '13 at 17:11
    
it certainly will work the same way ... as in both cases (or actually in all members of the mins family) the aromas are in the oils produced in glands on the leaf. –  Martin Turjak Jul 23 '13 at 17:16
    
I believe so, too. While I've never had nor tried to make "lemon balm extract", the same process should apply to virtually any aromatic herb. Now whether the results will be pleasing or usable... I think you have an interesting experiment on your hands. Let us know! –  Robert Cartaino Jul 23 '13 at 17:18
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And @RobertCartaino I think the "boiling and condensing" that the OP talks about would actually be distillation ... which is separating mixtures based on differences in volatility. And I think it might work in the case of the essential oils in mints, and might then get you pure mint oil ... but you would need special equipment. –  Martin Turjak Jul 23 '13 at 17:23
    
@MartinTurjak Thanks. I missed that initially, but I added the information to my post. –  Robert Cartaino Jul 23 '13 at 18:31
  1. Yes, many oils or lipids are dissolved in alcohol, whereas they cannot dissolve in water. This is why, for example, vanilla extract is based on alcohol.

  2. That would depend on the ratio of leaves to vodka, and how long you steeped. Probably no where near what commercial extracts are.

    It would be unlikely to be drinkable straight, since the flavor would probably be harsh and unpleasant at best, but that is speculation. You might be pleasantly suprised. I would think, though, to make something palatable, you would need to add sugar, and perhaps some vanilla or other flavorings to balance out the product.

    For example, these recipes for mint liquor

    do include sugar, and other flavors. I suspect the glycerin in the first recipe is for mouth feel.

  3. I doubt it, as oil can dissolve in alcohol, not just get mixed in.

Perhaps someone more knowledgeable with this process can give you more details. This is just based on a basic knowledge of chemistry and the foods.

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A different reason why 3. won't happen: vodka doesn't freeze at temperatures of home freezers. –  Mien Jul 23 '13 at 16:00
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As to #3, a while ago I found this recipe for mint essence, where they claim to have separated the oil from vodka by freezing. They add a photo, where you can kinda see a thin layer of something on top of the rest of the liquid, but it could also be the contact angle. @Mien they don't say what freezer they used in the recipe, but I think they state that the temperature separates the oil out and doesn't necessary freeze the vodka. –  Martin Turjak Jul 23 '13 at 16:08
    
Aha! That's the reference that gave me the idea about freezing. I was a little dubious about it, but wanted to be sure... –  Kelsey Rider Jul 23 '13 at 17:10
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@KelseyRider I just want to add here what rumtscho said in chat about this: "Yes, this can be done. Used to be done to make strong alcohol before they discovered distillation, actually It is rather inefficient, so not used any more." See Freeze_distillation. –  Martin Turjak Jul 23 '13 at 17:27
    
@Martin: The photo you gave doesn't look like freeze distillation, though, since both phases seem to be liquid. What might be happening is that the solubility of the mint oil in vodka may be reduced at lower temperatures, so that, if the initial solution is concentrated enough, some of the oil may be forced out of solution (possibly along with some of the alcohol) when the temperature is lowered. That's just a barely educated guess, though; it's hard to tell what's really going on just by looking at a picture. –  Ilmari Karonen Jul 23 '13 at 23:15

Freezing might work. Yes alcohol won't freeze but it doesn't have to and it may be better if it doesn't. The alcohol and mint oil are a solution so the oil is suspended in the alcohol. Depending on the freezing point of the mint oil it might separate out. Or the viscosity may change enough to allow for some separation. Think of motor oil in the winter being very think and alcohol remaining very liquid.

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