# Onion skin: why it cracks and falls off, and how we protect it

Onion skin cracks, falls off and darkens because of harvest, weather, curing and handling. What decides it and how we protect it so onions look good in the net.

Onion skin cracks, falls off and darkens for several reasons. Among the causes are moisture in the windrows, lying too long in the field, poor curing and mechanical handling. How an onion looks in the net is decided by several stages, from variety to loading. For a packing house this is not cosmetics: the customer sees the skin, not the flesh. We grow around 250 ha of onions and release them from our 13 000 t store, so we watch the skin from the field to the loading bay.

## Why skin matters commercially

A packing house sells onions through a net. Dry, tight skin of an even colour means fresh, firm produce. Skin that comes off in sheets, or is brown and blotchy, catches the eye even when the flesh is sound.

The Wageningen handbook on onion growing (2003) names three traits that make a good batch: firmness, skin adherence (huidvastheid) and deterioration of the outer skin (discolouration, spots), in Dutch verwering.

The reference point in specifications is the UNECE FFV-25 standard. In the Union, onions fall only under the general marketing standard, so FFV-25 is the language that supplier and packing house speak. For onions intended for storage it requires that at least the two outer skins and the neck are completely dry. Class I allows superficial cracks and partial absence of skin, provided the flesh is protected. Class II allows cracks and absence of skin on up to 1/3 of the surface, provided the flesh is not damaged, as well as signs of scuffing. We describe the tolerances in our post on [onion quality classes under the marketing standard](/blog/klasy-jakosci-cebuli-norma-handlowa).

{% callout tone="info" %}
A cracked or partly scuffed skin does not mean a spoiled onion. The standard allows for it as long as the flesh is covered. The problem is commercial: the less skin, the worse the look in the net and the faster the bulb dries out.
{% /callout %}

## What decides the skin

Every skin defect starts at a different point in the chain. We set them side by side with what we do on our side.

| Cause | What it looks like on the onion | What we do |
| --- | --- | --- |
| Variety | thin, loosely attached skin that rubs off easily; according to Wageningen, adherence differs between varieties, and high nitrogen fertilisation can make it worse | we base our range on Hybelle, Hysinger, Hyfive, Nation, Revelation and Bingo, that is firm, well-covered onions of the Rijnsburger type |
| Maturity at harvest | harvest too late: regrown roots that later crack the skin | we choose the harvest date to match the maturity of the onions; the Institute of Horticulture points to a threshold of 70-80 percent of tops collapsed |
| Weather in the windrows | brown patches on the side lying on wet soil, dark spots and cracking after lying too long | the Grimme WV 180 lays the onions in windrows to finish drying, the AVR Puma 3 picks them up from the windrows, and we finish curing in the store |
| Curing | wet skin darkens, over-dried skin cracks | we cure in the store for 2-4 days |
| Storage | roots and tops growing out crack the skin, moisture discolours it | only dry onions with a closed neck go into storage, and we check batches while they sit |
| Mechanical handling | scuffing, skin coming off in sheets | we select the batch for firmness, colour and dry skin |

## Harvest and weather: what happens to the skin in the windrows

The Institute of Horticulture's integrated onion protection methodology states that the optimal time to harvest onions for storage is when around 70-80 percent of plants have collapsed tops, but 3-4 leaves are still green. Harvest delayed until the tops have dried out completely causes the onions to root again. Roots and tops growing out in the store crack the dry skins covering the onion.

Next, the windrows. According to the Institute of Horticulture, curing onions in the field should not last longer than 7-10 days, because it worsens the quality of the dry skin: uneven colouring, dark spots from diseases and cracking appear. A FAO review adds that in wet weather the side of the onion lying on damp soil can show brown discolouration, which lowers its commercial value.

We harvest in two stages: the Grimme WV 180 windrower undercuts the onions and lays them in windrows to finish drying, and the AVR Puma 3 self-propelled combine picks them up from the windrows. Then we cure the onions in the store.

{% captionedImage src="/images/galleryPage/8.webp" alt="A windrow of lifted onions lying in a row in the field under a cloudless sky" caption="A windrow of lifted onions, from which the combine picks them up." /%}

## Curing and storage: dry, but not too dry

After harvest we cure the onions in the store with a stream of warm, dry air for 2-4 days. How this goes step by step, we describe in our guide to [curing onions before storage](/blog/dosuszanie-cebuli-przed-przechowywaniem).

Over-drying does harm too. According to a FAO review, at relative humidity below 60 percent, excessive water loss appears and the outer skin cracks. The same review, interpreting the OECD standard, admits that small cracks that form in dry air are tolerated as long as the flesh is not visible.

Moisture works the other way. The Wageningen handbook notes that skin discolouration forms more easily right after curing than later in the storage season, and that ventilating cool onions with warm outside air makes them damp and favours skin discolouration. That is why after curing the onions are to stay dry. We gave the condensation of water on cold onions taken out of the store a separate post, about onions sweating. We gather the whole way we take onions through winter in our guide [storing onions](/blog/przechowywanie-cebuli).

## Mechanical handling and sorting

The skin is thin, and every transfer and every pass over a sieve strips a little of it off. The UNECE standard counts signs of scuffing among Class II defects, and in our post on [mechanical damage at vegetable harvest](/blog/uszkodzenia-mechaniczne-przy-zbiorze-warzyw) we describe that in onions scuffing means losing the dry skin.

We sort onions on the DOWNS CropVision optical sorter. Cameras and AI scan every bulb through 360 degrees and reject stones, clods of soil and defective bulbs, at up to 100 t/h. We assess the skin when selecting a batch: we select every batch for firmness, colour and dry skin.

## How we protect the skin on our farm

Skin cannot be restored, it can only be lost, so we protect it from the field: we choose firm, well-covered onions of the Rijnsburger type, harvest in two stages, cure in the store and then select batches for firmness, colour and dry skin. We produce onions using a technology free of pesticide residues, in line with the principles of Integrated Plant Production. With a yield of around 60 t/ha and 250 ha of onions, every one of these stages concerns thousands of tonnes.

You will find sizes, packaging and batch availability in our [onion offer](/oferta/cebula). If you need a sample to judge the skin yourself, write to us through the [contact form](/kontakt).

## Frequently asked questions

### Why does onion skin crack?

Among other things from over-drying, or from roots and tops growing out. According to a FAO review, relative humidity below 60 percent causes the outer skin to crack, and according to the Institute of Horticulture, roots and tops in the store crack the dry skins covering the onion.

### Why does onion skin fall off?

Usually from scuffing at harvest, transfer and sorting. In onions, scuffing means losing the dry skin. Variety matters too: according to Wageningen, skin adherence differs between varieties, and high nitrogen fertilisation can make it worse.

### Why does onion skin darken?

The cause is often moisture: wet windrows, contact with damp soil, insufficient curing and condensation of water on the onions. The Institute of Horticulture also links dark spots on the skin to diseases that develop when onions lie too long in the field.

### Does a cracked skin disqualify an onion under the standard?

No. According to the UNECE FFV-25 standard, Class I allows superficial cracks and partial absence of skin if the flesh is protected, and Class II absence of skin on up to 1/3 of the surface if the flesh is not damaged. A packing house may have stricter requirements in its specification.

### How do you assess the skin when receiving a batch?

It is worth looking at the onions through the net and taking out a few bulbs: the skin should be dry, tight, of an even colour and should not expose the flesh. Skin that is damp, brown or coming off in sheets is a signal to talk to the supplier. On request we send a free sample.