Have you ever been to a restaurant, ordered roast lamb, and it either came with a green mint jelly that was so artificially green or a dull, brownish color fresh mint sauce?  Have you made your own mint sauce that turned immediately dark and wondered how to make a vibrant mint sauce.

During a family meal recently, one of the family members was making the mint sauce. She was chopping the mint by hand with a Chinese cleaver.  Although the taste was good, I noticed that the mint sauce was not as bright as usual.  It made me wonder since there were no ingredient changes.  It turns out that the technique and utensils used have an effect on the outcome of the sauce...purely aesthetic, but good to know when entertaining company!

Here are some tips on how to make a vibrant mint sauce. First... 

Why does the mint turn brown?

Oxidation.

Fruits and vegetables contain an enzyme called polyphenol oxidase which, when exposed to air, reacts with oxygen causing a reaction called oxidation and turning the fruits and vegetables brown.  

Corrosion.

It is also known that a knife that has corrosion, rust spots, is apt to cause your the mint to brown faster.

Using the wrong vinegar.

I hate to state the obvious, but a red, malt and especially balsamic vinegar will result in a darker mint sauce. 

How do you reduce browning?

Acid reduces oxidation.  Acid can be in the form on any citrus juice or vinegar.  If chopping the mint by hand, soak the mint leaves in an acid dilution for a few minutes. Also, make sure that you are not chopping the mint with a knife with rust.  (Authentic Chinese cleavers made of iron are susceptible to rust spots.  It is preferable not to use this type of knife for chopping the mint.)

If using a hand blender, add the vinegar together with the mint and blend.  When the mint breaks down, it immediately makes contact with the acid and thus reduces oxidation.

Oxidation will still take place but at a much slower rate so don't make your sauce too far in advance of serving it!

It is preferable to use either a white wine vinegar or rice vinegar. The clearer the better.

Hope this helps!