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Why Does Basil Turn Black After Washing? (Explained)

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Last updated on November 26th, 2022 at 06:26 am

Do you often think of basil when you think of a nice Pesto sauce? Then, your mind must have branched to consider the significant ingredient for that sauce-lush green basil leaves.

It is disappointing to find freshly cut basil leaves turning black after washing them.

So, why does basil turn black after washing? The reason is mainly due to the leaves’ temperature change and moisture content. As we know, water introduces a drop in temperature, accompanied by an already mild room temperature, especially in air-conditioned houses.



For first-time users, it is always alarming to see basil turning black or brown after washing every single time.

It is mind-boggling when grown at home, and the uncut leaves still show no color. However, this occurrence raises yet another question.

Is it normal for basil to turn black? After washing and being allowed to stand, it is normal for basil to turn black.

Just as spilled sugar will attract ants with time, so does moisture on pruned basil leaves attract black coloration. 

Please note that when I say it is normal, I do not necessarily mean proper! It usually is only in the cause and effect sense, i.e., the black coloration is only a repercussion for excess moisture on nipped basil.

Yet, it is not proper, and thus you can avoid it. Want to know how? Then, read on! After all, what is basil without its characteristic flavor in our food, and as you can guess, that flavor declines with the disappearance of its bright green color?


It could have just been sheer admiration for the lush green or a desire for closer proximity to basil because of its numerous uses and benefits you decided to grow this plant.

After all, it is easy to grow and requires little effort to cultivate. Yet, you are disappointed to find them turning black after a wash whenever you harvest your basil.

You might ask, “why is my basil turning black”? Simply put, it results from excess moisture in the leaves and a sudden temperature change, usually to a lower temperature, just as we stated earlier.

It is essential to remember that most basils originated from India, a tropical climate. This situation affects basil in two significant ways.

First, it absorbs a lot of water stored at the roots (not leaves) and is rapidly translocated by active vascular tissues ensuring an even spread across the leaves.

Thus when you harvest the leaves, the vascular tissues in them die.

Second, when soaked in water for washing, the leaves have nowhere to store the readily available water, nor tissues to translocate them begin to blacken.

The second-way basils are affected climatic. Having originated from the tropics, basils thrive in the presence of sunlight and a reasonable degree of heat.

It becomes problematic when there is a sharp change in this desired temperature, especially after harvest when the plant cells are weakest and cannot carry out homeostasis (i.e., balancing the internal body temperature).

This occurrence again results in the black coloration of leaves. But, then, it is not just your basil. Very much any basil will also turn black under these conditions.

That is why supermarkets do not refrigerate basil leaves and limit their supply to the day’s needs only while properly aerating them openly to prevent any color change.


Why Does Basil Turn Black After Washing

To solve a problem, one has to know how the situation came into existence.

In this case, it is not enough to know that it is normal for washed basil leaves to turn black. It is also essential to understand why.

So, what causes basil leaves to turn black? The reason ranges from pest infestation, fungal and bacterial infection, and actions of enzymes down to the rotting of basil roots. Let’s now look at these causes.

Though we may sometimes only notice the blackening of basil leaves after harvest and washing, this may have begun while attached to the plant stem due to pest action.

When pests feed on the leaves, they also excrete on them.

Thus, a reaction occurs between the feces of the pest and the leaves since they are both organic matter, to the detriment of the plant leaves.

A similar situation occurs when fungi (Colletotrichum Fungi) and bacteria (Pseudomonas Cichorium Bacteria) attack the plant. Again, the effects may begin to manifest as you harvest the plant.

When there is no food to break down in the human stomach, the worms begin to feed on the stomach walls, causing stomach ulcers.

The same happens when you harvest basil leaves since the enzymes receive no more nutrients from the soil.

They feed on the leaves themselves, causing black coloration in the leaves, indicating the death of cells.

When roots rot, they cannot spend enough nutrients on the other parts of the plants, including the leaves.

Hence, the leaves of a basil plant with rotten roots may look green on the plant but will lose that coloration, trading it for black once soaked in the trace cell nutrients are dissolved.

Other trivial reasons have been discussed earlier in the preceding paragraph, i.e., temperature and moisture.


Having seen that the reasons could be trivial or disease-related, you may ask; Is it safe to eat black basil?

Of course, the flavor is long gone, yet some still consider it edible. True, but with a strikingly bitter and repelling taste.

In my opinion, when confronted with black basil. It is always better to let go. But, again, you never know when you are eating dormant bacteria!

Still, how can you keep your basil lush green even after harvest?

Why not try doing the following:
1. Wash with running water rather than just soaking.
2. Keep freshly cut basil in a vase with water as you do for flowers.
3. Keep harvested basil on the veranda before introducing a much cooler room temperature.
4. Whenever possible, only buy or cut basil leaves when about to use them.


I cannot overemphasize the nutritional value of basil leaves, yet a contaminated leaf adds no value to the consumer, not even a pleasant taste.

Furthermore, Basil leaves turn black under certain conditions discussed above, limiting their usefulness.

Thus, to benefit from basil leaves, always have them fresh and green whenever possible.


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