White onion or Allium cepa (“sweet onion”) are a cultivar of dry onion which have a distinct light and mild flavour profile. Much like red onions, they have a high sugar and low sulphur content, and thus have a relatively short shelf life.[Bill Jones ] White onions are used in a variety of dishes, such as those of Mexican and European origin. Their uses in dishes often relate to their mild nature, they are often included in dishes to provide a light, fresh and sour taste to dishes and are often added uncooked to dishes such as salads.
Flavour profile and culinary uses
White onions have a distinctively mild flavour palette in comparison to other onion
such as the
Red onion and
Yellow onion onions. They are distinctly less
Pungency and have a lighter flavour on account of their relatively high
sugar and low
Sulfur content than other onion types. Because of this mild and easily palatable flavour, white onions are often used
Raw foodism in dishes such as
and
. When raw white onion is soaked after being finely chopped, it adopts a relatively
Sweetness flavour profile as it loses its
Astringent.
[Alison Delany , All the Types of Onions, and What They're Best For
]
Retrieved 13 October 2020
Due to this flavour profile, white onion is versatile in its uses for food. Its use is often central to the construction of salads as it provides a fresh, but not overwhelmingly pungent flavour sensation. It is also widely used as a central ingredient in the making of as its light flavour does not overpower the other elements of the dish, contributing to a cohesive flavour palette. White onion is also extremely useful as a component in Fermentation dishes such as coleslaw as its low astringency allows it to adopt a largely sweet flavour in the dish. It also has many uses in dishes such as salsas because of this low astringency.
Diseases affecting white onions
Onion Smudge
The parasitic ‘Onion Smudge’ (“
Colletotrichum circinans (Berk.) Voglino”) is a disease which affects crops of onion subspecies internationally, at all stages of development. Agricultural scientist, James Charles Walker notes that white onions are especially susceptible to infection of onion smudge due to the lack of pigment in its outer shells, as coloured onion subspecies contain a higher concentration of
phenolic acid in its shells.
[James Charles Walker, “Disease Resistance in the Vegetable Crops”. Botanical Review, 7(9) (June 1941), 483] Onion smudge thrives in damp soil conditions of above 20 degrees Celsius. The fungus can survive in the soil of onion plantations, and thus is extremely dangerous as it can impact the yield and performance of future crops.
Onion smudge causes damage to the outer scale leaves of the white onion, damaging the cosmetics of the bulb and ultimately reducing its market value. If the smudge is unnoticed in its early stages and the onion is left untreated with other onions. The parasite has the potential to infect the entire crop and cause the degeneration of the scale leaves, premature sprouting and the creation of conditions in which further storage rot may occur.
Onion White Rot
White Rot (
Sclerotium cepivorum) (also known as Allium Root Rot) is a notorious and severe fungal disease which impacts most members of the
allium family, including
garlic,
and
onion varieties.
The
fungus is unique in that it does not produce
of great significance in its lifetime. Rather, it exists in the soil as a hardened fungal mass known as
Sclerotium, which remain detached and dormant in the soil until there are favourable conditions and it can attach itself to a host.
Given the resilience of the fungi, it can remain in the soil for over 20 years, rendering many fields unviable for the planting and harvesting of onions.
White Rot can spread throughout a field, or from field to field by means of flood or , agricultural equipment or other organic materials, such as plant scales blown by the wind.
Botrytis Leaf Blight
Botrytis Leaf Blight (
Botrytis squamosa) is a fungal disease which mainly affects
in the allium family, particularly onions.
The impacts of Botrytis Leaf Blight are mainly seen in the leaves of the plant. After infection, the fungus causes leaf spot (also known as leaf
), and the maceration of the foliage tissue of the plant, resulting in dieback and blighting.
The lesions are initially often whitish and approximately 1-5mm long, with a light green halo that appears wet surrounding it.
The lesion then usually becomes sunken and straw-like into the stages of fungal development and may develop a slit in the lesion. Severely affected plants may result in a significantly smaller bulb size and a blighted appearance.
The Botrytis Leaf Blight pathogen survives the winter much like White Rot does, as Sclerotium (a small mass of fungi capable of thriving in hostile conditions).
Onion Downy Mildew
Onion
Downy mildew is a disease that is caused by the
oomycete Peronospora destructor.
It is a foliar disease, and causes leaf to become pale green, then tan, brown or yellow and finally collapse.
The fungus is extremely infectious to white onion
and can often be first observed by patterns of yellowing within a field of onion crops.
Such patterns often correspond to the direction of the
prevailing winds, enlarging as the disease progresses.
On individual plants, signs of Peronospora Destructor can be visible, as fine, furry growths that have a greyish white colour.
These growths are susceptible to further infection by diseases such as Purple Blotch of Onion or Stemphylium Leaf Blight of Onion, and if infected, can produce purple pigmentation of lesion and dark
.
The Peronospora Destructor pathogen only produces spores in live hosts, and releases spores at night, when there are cold temperatures and easily be blown across crops and infect other plants.
Planting of white onions
There are multiple methods of
Sowing white onions:
-
Onion Transplanting: a method by which started in the current growing period are bought and planted in one's own garden. This method often yields quick bulb growth, but the plants are more vulnerable to disease in maturity.
-
Onion Sets: small from the previous harvest are not allowed to mature and are dried. These bulbs are used in the current season, and often grow the quickest out of all planting methods and produce larger than natural bulbs.
-
Onion : seeds of the white onion that can be planted into sets in late Spring. While this method may have the longest grow time (up to 4 months for mature bulbs), the onions produced are the least susceptible to disease.
Different varieties of onions vary in the time of year at which a mature white onion is cultivated:
-
Short-day onions are onions that form bulbs when they are in an environment where they get 10 to 12 hours of sunlight a day.
-
Intermediate day onions are onions that will form mature bulbs when they are in an environment where they get 12 to 14 hours of sunlight a day.
-
Long-day onions are onions that form bulbs when they are in an environment where they get 14 to 16 hours of sunlight a day.
For most white onion varieties, a soil pH of 6-7 is optimal. At times when the pH of the soil for onions is below 5.5, magnesium and molybdenum supply is inadequate and at a pH of above 6.5, zinc, manganese and iron are less present in the soil.
External links
