Forum Basil and spinach pesto

I tried this recipe and it was the first time ever that my husband could not finish his meal. It was terrible. 

The reason for putting oil on top is to create an airtight barrier thus stopping the oxygen in the air coming into contact with the pesto. When there is no oxygen (air) there can be no oxidation, inhibiting the growth of food spoiling microbes. The reason for creating an acidic environment ie using lemon / lime juice is to further inhibit the growth of organisms which break down (rot) the food. The idea behind low oxygen and acid environment is that it inhibits the growth of food spoiling organisms. Not sure about the oxalic acid in spinach but spinach does decompose (rot) very quickly once picked. So freshest is best. The same reason why we add salt to food eg. vegie stock concentrate and keep food at low temps (fridge). All work to preserve by inhibiting the growth of food spoiling organisms. That black colour is actually decomposed food!  Kind Regards Anne

Make sure you use lemon or lime juice as it will stop the oxidation process. I had something similar happen when I used spinach in the pesto. I now only use basil. Spinach has a high amount of oxalic acid so oxidises very easily and quickly.

I don't ever use oil on my pesto (when storing). All the oil would do is create an" airtight" barrier so that the leaves would not come in direct contact with the air.

Hope that helps.

Hi Kerry, we're sorry for the late reply. Yes it's unusual for the pesto to turn black. It's possible that the batch of basil has oxidised as annebarnes has mentioned above. This will cause the leaves to darken and could have created the black swirls. Make sure you keep your pesto under a layer of oil to preserve the pesto and try and use the freshest ingedients possible. We hope this helps.

This sounds to me like oxidation ie coming into contact with the air, of the basil leaves, same sort of thing as apples, bananas going brown when cut. I have found that basil leaves go off very quickly especially those sort that are grown in small pots, and sold in supermarkets. These will rot very quickly and turn black. Maybe your basil may not have been the best? It is a good idea to carefully pick through the basil you are using especially if it is bought. Also pesto keeps much better under a layer of oil. I don't know if this is the case but if the pesto was exposed to the air and then you stirred the jar you could be putting some of this oxidised basil through the mix inadvertantly this may cause black streaks. I really hope this helps, Anne :) The same could apply to the spinach leaves as well.

Hi Kerry, can you please advise what recipe you used?