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Twice I have tried to make a fresh mint liqueur (flavored vodka), and both times it has turned a very unpleasant brown/black color. I'd like to figure out how to do this while keeping the nice bright green color, or even no color. The discoloration is also associated with a change in smell - not completely unpleasant, but not the same mint.

The method I tried is just the standard that you read on the first 10 google hits, or the question found on seasoned advice. Wash the mint leaves, put in alcohol, let sit, add sugar syrup, possibly glycerin, and enjoy.

The first time I did this, I left the stems in the mix out of laziness. I let it steep for a week or two, and it was completely brown/black.

This second time I removed the stems, and I also only steeped the leaves for 24 hours. I also used a glass weight to keep the leaves completely submerged. After the 24 hours, I strained the flavored vodka into a clean jar and put it in the cupboard. The mint vodka was always kept in the dark cupboard, at room temperature. 24 hours later, the top half of the vodka had already discolored, and an additional 24 hours later, all of the vodka had browned.

I had hoped that the discoloration was due to something in the leaves oxidizing(?), and that by removing the leaves after a short time, I'd remove what was causing the browning. Sadly, the alcohol appears to have extracted whatever is browning. Note: the leaves themselves also browned in a similar timeframe, and from the top down (they were compacted in the original jar).

The mint is a spearmint variety, for what that's worth. I've not tried it on a different mint, b/c the variety I used is my favorite.

Any ideas on how to prevent the discoloration?

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    Not an answer as I haven't tried it myself, but I wonder about adding acid. You could try a small test batch with a little lemon juice or citric acid added at the same time as the leaves. My rhubarb liqueur did the same, and my creme de cassis is heading in that direction (after a few years). – Chris H Jun 4 at 21:20
  • I can try that. I wouldn't expect it to change things that much as vodka is somewhat acidic already (~4.0 pH), and I would expect rhubarb to be acidic already... – Trey Jackson Jun 4 at 23:42
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    I didn't try it for the rhubarb, which I only made once, and if the vodka is already acidic (I assumed it wouldn't be) extra acid might not do much. Commercial mint liqueurs I've seen are either clear or lurid green (artificial?) so it should be possible to get an extract that doesn't brown – Chris H Jun 5 at 5:55
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    Not an answer, because it sounds like you want to use fresh leaves, but I would try drying out the leaves so you essentially have a teabag and use them instead. – Bee Jun 5 at 14:01
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    Have you tried shocking it before the infusion? (dip in boiling water for a few seconds, then a dip in ice water). It helps when making herb pastes; I don't know if it'll have an affect on infusions. – Joe Jun 5 at 19:16
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Idea 1: Assuming the leaves are oxidizing: you could add an antioxidant. Vitamin C is handy and will scrounge up oxygen radicals. Crush up some pills and shake them in. It will make it a little sour too - ascorbic acid is vitamin c.

Idea 2: deplete your alcohol solution of dissolved oxygen first. When you heat something to near boiling, the first wave of bubbles is gas coming out of solution. Do that with your alcohol. Add it steaming hot to your steeping vessel (maybe heat up vessel first with warm water so it doesn't crack!), put in mint and then cover it airtight. Maybe that will exclude enough O2 to keep things green. Also would serve as the blanching step in linked article.

I was pleased to see the vitamin C idea was listed in the linked article about keeping pesto from turning black.

https://www.thekitchn.com/good-question-w-4-12832

Pesto is made with basil which is a mint so the same issue as you have. The other recommendations from that article are blanching the basil (yah!) and adding lemon juice (vitamin C!).

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