The Importance of Fruit Quality Control & Ripeness Testing for Lemons

While you might not grab a lemon as a juicy snack, they are one of the most common fruits for cooking and baking, including the zest and even the leaves – often used to make tea. Lemon oil is also used in aromatherapy!

Optimizing lemon fruit quality control and ripeness testing has an impact on the whole value chain, from growers and pickers, to warehouses, marketing companies, wholesalers, online marketplaces, retailers, and consumers. If you can successfully optimize the way that you approach quality control for lemons at each stage, whether that’s growing and harvesting, or shipping and storing, you can reduce waste, and also increase your profit and the productivity of your workers.  

That’s exactly what we’re doing at Clarifruit, by introducing a streamlined lemon quality standard for all stakeholders, using the Clarifruit platform which is based on AI and analytics.

Common Defects when Growing & Harvesting Lemons

The following lemon defects are the ones that are most likely to affect lemon quality across the supply chain:

Spray Damage

Spray burn in lemons can damage the rind, so it’s important to be careful to think about different kinds of nutritional additives or pesticides you use when growing lemons. Some post-harvest treatments can also cause ring patterns at the points where the lemons touch one another inside containers.

Sooty Mold

Sooty mold fungi when lemon testing results from honeydew secretion from insects including aphids, mealybugs or scale. This black mold can be found on the leaves and other parts of the lemon tree.


This type of peel injury when you’re working with lemons is often triggered by high temperatures when the fruit is stored. You’ll often see clusters of collapsed oil glands scattered over the surface of the lemons.

Citrus Canker

While not dangerous to humans, citrus canker will cause lesions and bumps on the leaves, stems and fruit of a lemon tree, usually caused by heavy rainfall and high temperatures.

Citrus Mites

Citrus mites can be brown, yellow, rust-colored and red and are closely related to ticks. The leaves of lemon plants infected with citrus mites can become spotted or silvery in appearance. The mites will feed on all parts of the plant.


This is a fungal infection that is usually found in other citrus fruits, but can impact lemons, too. It tends to happen on overstressed trees and plants, and can be identified by circular tan spots with an outer rim of purple.

Fungus Knats

Overwatering a lemon crop can create an ideal environment to attract fungus gnats. In fact, overwatering is one of the main reasons a citrus crop fails.

Stem-End Rot

Also known as Diplodia citrus rot, stem-end rot is usually found in sub-tropical regions. It comes from a particular fungus which starts in the stems, but can then quickly move over the fruit causing progressive decay in lemon quality.

Nitrogen Deficiency

If your lemon quality is suffering from a Nitrogen deficiency, tree growth will be limited, and fruit will have light green or even yellow foliage. Although this same result can happen due to overwatering, if you’re sure that this isn’t the case - a nitrogen deficiency is likely to be the problem.

Phosphorous Deficiency

If phosphorus is too low in your lemon trees, growth will be impacted. You can spot this issue when older leaves take on a reddish-purple coloration, and they can even start to look burnt.

Alternaria Rot

If you see dark brown or black decay on your lemon citrus fruit, this could be down to rot. It’s usually a storage problem rather than found in the field. On the navel of the lemon, it is called black rot.

Blossom End Rot

Signs of this kind of rot are brown patches, and an earlier than usual fruit drop. This comes from lack of calcium in the soil, or because of irregular watering.


Lemon quality can be impacted by bruising at any point, either due to improper handling at the picking stage, and poor storage or transportation. This will impact consumer demand and could result in a lower price for your container.

Frost Damage

If your lemon cropis at freezing temperatures for a long period of time, it may cause freezing damage, which is regularly internal so cannot be seen at a glance. The impact on the lemon quality standard will depend on the tree’s previous irrigation, the health and age of the tree, and whether the location is exposed.


Wrinkles can be caused by many issues with a lemon yield, including challenges during irrigation, sour rot or damage from thrips and other insects.

Green Mold

When you are testing lemon quality, your testers may spot green mold. The initial decay often appears with a soft watery spot that is firmer than sour rot. Millions of olive green spores are created. During handling, these are dispersed, which means healthy fruit in the same containers can be ruined very quickly.

Interesting Facts about Lemons

Common Quality Attributes for Growing and Harvesting Lemons

The following internal and external lemon attributes are commonly used for quality evaluation:



Sugar/Acid Ratio



For the full list of attributes that the Clarifruit platform currently evaluates and recommended quality standards for each, download our free app now.

The Clarifruit platform also integrates with 3rd-party technology to evaluate external lemon attributes. Learn more here.

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