Cull onions: comparing moisture and dry-matter analysis

Why moisture and dry matter matter in a cull onion order

Moisture and dry matter answer two different purchasing questions. Moisture is the water in the product; dry matter is everything left when that water is excluded. For a bulk buyer, the distinction affects how much of a delivered load is actual dry material and whether nutrient figures can be compared fairly with other ingredients.

Cull onion usually means bulbs rejected from fresh-market sale, not a standardized processed ingredient. A lot of raw bulbs contains both water and onion solids, and its moisture can affect the amount of dry matter in each delivered unit of weight. Dry onion products have had water removed, while onion peel is a distinct material rather than simply another name for whole cull bulbs. Their analyses should not be treated as interchangeable.

Read the analysis basis before comparing figures

An as-received, or as-fed, figure describes the nutrient concentration in the product in the condition sampled, including its water. A dry-matter figure describes nutrient concentration after the water is mathematically excluded. The number can therefore look higher on a dry-matter basis without any increase in the amount of nutrient in the original product.

To convert an as-received nutrient concentration to a dry-matter basis, divide it by the dry-matter fraction. Dry-matter fraction is one minus the moisture fraction. To convert a dry-matter figure to an as-received basis, multiply it by the dry-matter fraction. Use the moisture result from the same sample or analysis context; otherwise, the conversion may not represent the material being compared.

Keep units and basis labels attached to every result. A nutrient percentage without its basis is incomplete for a meaningful comparison. If two offers report the same nutrient using different bases, convert them to the same basis before evaluating their concentrations.

Translate delivered weight into dry matter

The delivered scale weight of raw cull onions includes water. To estimate the dry matter represented by that weight, multiply the delivered weight by the dry-matter fraction. This makes the comparison with a dry ingredient more useful than looking at gross weight alone, particularly when the purchase decision depends on solids or nutrients rather than water.

For example, let W represent delivered product weight and D represent the dry-matter fraction. The dry matter delivered is W × D. This is a calculation framework, not an assumed cull onion specification: the buyer needs the actual lot’s moisture or dry-matter result to apply it.

This distinction also matters when comparing quoted prices by weight. A lower price per delivered unit does not, by itself, show which offer supplies more dry matter. Any price comparison that adjusts for dry matter should use the quoted quantity, the same weight units, and a relevant moisture result for each offer.

Keep raw bulbs, dried onion, and peel distinct

Raw cull bulbs, dried onion, and onion peel differ in physical form and composition. Removing water concentrates the remaining solids by weight, so nutrient percentages expressed on an as-received basis can differ simply because the products contain different amounts of water. Dry-matter reporting helps separate that water effect, but it does not make different product forms nutritionally identical.

Peel is a separated part of the onion, not whole-bulb material that has merely been dried. Differences in plant part and processing can affect the material represented by an analysis. Buyers should compare like with like where possible, and should not apply a dried-onion or peel analysis to raw cull bulbs without evidence that it represents the offered product.

For feed formulation, the appropriate comparison depends on the ingredient’s intended role and the nutritionist’s evaluation. Moisture and nutrient basis help interpret the analysis; they do not establish a universal feed specification or suitability for every ration.

What to request when evaluating an offer

Ask what the material actually is: raw cull bulbs, dried onion, peel, or another defined form. Request the moisture or dry-matter result and the basis used for each nutrient figure. For a lot-specific comparison, the analysis should identify the sampled material and make clear whether results are as received or dry matter.

Then compare offers on a consistent basis and relate the analysis to the quantity being purchased. If a result is unclear, ask for the original report or a corrected presentation with the basis stated; a number without that context cannot support a sound comparison. Commercial terms such as available quantity, packaging, timing, and delivered price depend on the particular offer.

For buyers seeking raw cull bulbs, the [onions ingredient page](/ingredients/onions) is the natural next step for sourcing. Include the intended product form and the analysis questions that matter to your comparison when describing the requirement.

Common questions.