Short answer The cause of pesto turning brown, or grey is usually because the herbs have started oxidising. The best way to slow that process is to reduce the amount of time the sauce is exposed to air.
Long answer First things first, if you accidentally leave your homemade or store-bought pesto out overnight and wake up to find it has changed colour, then we strongly advise you to discard the whole batch.
If, on the other hand, the jar has been opened and left in a fridge for a day or two, it's most likely that the change in colour is simply a result of oxidation. This is a chain reaction that happens in the presence of oxygen and is what causes the deterioration of food, making ita dull colour and sometimes resulting in off-smells or off-flavours too.
This oxidationis largely unavoidable and isn’t dangerous per se. Even though it's unlikely to make you sick, we recommend throwing away the jar. People eat with their eyes as much as their mouths, and life is too short to eat pesto that isn't in anything other than peak condition.
How do youslow down the browning of pesto? There's nothing anyone can do to completely stop pesto's colour change, but there are various things that producers can do to slow it down. The first is to briefly blanch the basil leavesbefore incorporating theminto the sauce. This destroys many of the decomposing enzymes that cause the browning in the first place.
Anyone who has ever tried to prevent an avocado from going grey will intuitively know that acids are helpful in slowing down the process too. We like a little citrus kick in our sauces, so the use of lime or lemon juice is a win-win for us. Our sauces also contain a tiny amount of vitamin E that can slow down oxidation.
How you can help stop your pesto from turning brown or grey The only way consumers can slow down the browning of pesto is by limiting its exposure to air once it is opened. Vacuum sealing is one option, but few people have that luxury in their homes.
The other way is to drizzle a thin layer of oil (ideally the same kind of oil used in the pesto) on top of your sauce before transferring it to your fridge. That little bit of oil basically creates a barrier between the sauce and the air and should at least halve the speed of browning and keep your pesto green for longer.
Prolonged exposure to air turns herbs bitter and may be accompanied by the telltale sign that the colour of the sauce looks more brown or grey than it did before. You can reduce the risk of oxidation by making sure that your half-eaten jar of pesto goes back in the fridge with a layer of oil on top.
The cause of pesto turning brown, or grey is usually because the herbs have started oxidising. The best way to slow that process is to reduce the amount of time the sauce is exposed to air.
Some swear by blanching the basil before using. This involves plunging it into boiling water, then immediately putting it into ice water to stop the cooking process. How does it work? The heat from blanching de-activates the enzyme responsible for browning.
If your pesto has turned brown instead of green, that's another clear sign that it's rancid. And there's always the smell test: it will have a strong sour smell once it turns.
If you see oxidation, which shows up as brown or gray discoloration, it's unlikely to be harmful, but it's not appetizing, so you may want to throw the pesto away. (If your pesto is homemade, you'll want to eat it in just a few days.)
Fill a jar, a vase, or a glass half-way or so with water and put the basil bouquet (trimmed-stems down) in the water. Make sure no leaves are in the water or they will turn dark and slimy. Cover the leaves and the entire jar of basil loosely with a plastic bag. Leave the covered jar of basil on your kitchen counter.
Pesto will last in the fridge for up to 2 weeks. If you've stored it in the freezer, it will last for 6 months. When you're ready to use frozen pesto, thaw it overnight in the fridge or place the container of pesto in a bowl of warm water for a quicker thawing time.
Browning happens most readily at neutral pH, so making the pesto's pH more acidic can help slow down this process. We found that lemon juice, which contains both citric and ascorbic acid, preserved the pesto's green color without compromising its flavor, adding just a hint of pleasant acidity.
Research has shown that temperatures below 53.6o F (12o C) can cause serious problems. The initial symptoms are brown spots. Eventually, the entire leaf darkens (black necrosis) and the plant will drop its leaves (leaf abscission).
The National Center for Home Food Preservation suggests it should be made fresh and stored in the fridge for no more than 3 days. However, it may be frozen for longer term storage.
Once opened, a jar of pesto lasts in the fridge for three days without any dramatic loss of quality. It will be perfectly safe for another two days, but leave it any longer, and its quality will decline to the point that it will no longer be enjoyable to eat.
Once your pesto has been opened, however, you should close its lid tightly, store it in the refrigerator, and plan to finish it within three days. This may seem like a short time window, but it helps ensure that you enjoy the highest-quality pesto.
To freeze larger amounts of pesto—from 1/2 cup and up—transfer the pesto to a sealable container, cover the surface of the pesto with a thin layer of olive oil, tightly seal the container, and place in the freezer. That layer of olive oil will minimize browning on the surface of the pesto as it freezes.
The Bottom Line. Pesto is higher in calories than some sauces but it's also made with super-healthy ingredients, like basil, olive oil and nuts. I find it's a great way to add more flavor to pasta dishes and even vegetables and proteins.
Like with any recipe that uses just a few ingredients, you'll want each one to be fresh and flavorful. Basil: Fresher basil and high quality olive oil are the two biggest differences between homemade and store-bought pesto. Grab the freshest basil you can find with little signs of limpness or browning.
To freeze larger amounts of pesto—from 1/2 cup and up—transfer the pesto to a sealable container, cover the surface of the pesto with a thin layer of olive oil, tightly seal the container, and place in the freezer. That layer of olive oil will minimize browning on the surface of the pesto as it freezes.
Pro tip: Some pesto can contain chlorophyll from basil, which can oxidize. If you notice a darker stain as a result of this, you can apply a paste of baking soda and water directly on the stain.Let it sit for up to 30 minutes and then rinse with cool water before washing the item.
Pesto can develop a brown layer on top when it's exposed to air. To prevent this, pour a thin layer of olive oil over the top of your pesto before freezing or refrigerating it.
To prevent browning, press a piece of plastic wrap directly on the surface of the avocado pesto and refrigerate for up to 5 days in an airtight container.
Introduction: My name is Aron Pacocha, I am a happy, tasty, innocent, proud, talented, courageous, magnificent person who loves writing and wants to share my knowledge and understanding with you.
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