Harvest 2021: Propionic acid supply issues impacting grain treatment

Production problems this year have led to supply and availability issues of propionic acid to treat grain on farms, according to the College of Agriculture, Food and Rural Enterprise (CAFRE) and the Department of Agriculture, Envrionment and Rural Affairs (DAERA).

Across Northern Ireland, using propionic acid or “prop-corn” as it is known, has been one of the most common methods of preserving grain.

It is relatively simple, yet effective and can normally be cost effective.

Propionic acid for grain

Application of propionic acid removes the need for grain to be dried.

The acid treatment has a twofold action – firstly it lowers grain pH to a level which prevents mould and mycotoxin growth, and also can improve energy levels of the grain for feeding to livestock.

A further advantage is that no specialised store is required; the anaerobic conditions developed as a result of the treatment will be sufficient to keep the grain from spoiling.

CAFRE crops development advisor Jonathan Brown, points out that “with supplies of propionic acid restricted this year, it will be important to achieve accurate application.

Jonathan Brown, CAFRE crops development advisor

This will avoid costly overuse, but it is equally important to ensure accurate assessment of moisture content of the grain to ensure enough is applied to safely store the grain, as under-application can also be a costly error if the grain pile spoils.”

Application rates are detailed in the table below. The rates given are for whole grain, and if the grain is being rolled, then application rates should be increased by 10-15%.

Propionic Acid Application Rates

Grain moisture % Litres of prop-corn/t Grain moisture % Litres of prop-corn/t
16 5.5 22 8.5
18 6.5 24 9.5
20 7.5 26 11.5
Source: CAFRE

This year due to supply issues and also an increased demand for this product, some farmers may have to consider alternative methods.

Brown went on to highlight the four main alternatives to propionic acid including drying, crimping, adding caustic soda or adding urea.


The aim is to harvest crops in as dry conditions as possible which is being helped by the current dry spell, ideally below 18% moisture, according to CAFRE.

Grain is then further dried down to 14-15%. This is most commonly done in NI through a mobile match drier. This method results with grain in a relatively stable state, with moisture removed preventing moulds from growing.

Costs for drying range from £20-£30/t depending on moisture percentage and handling charges etc.

Crops cut below 18% moisture can be stored for a short period without further drying if they can be ventilated through pedestals or under floor ventilation. However this would need to be carefully monitored to ensure it doesn’t begin to spoil.


Crimping also involves using an acid treatment or bacterial inoculants to create low pH anaerobic conditions.

During the process, grain is lightly crushed to maximise exposure to the acidifying additive.

Grain is normally stored in an air tight clamp or bag, and can be fed directly to livestock.

A further advantage of crimping may be the ability to harvest crops at a higher moisture content (30%) while still allowing grain to be stored successfully.


Historically this is used for treating feed wheat prior to storage. Unlike crimping, there is no requirement to roll the grain and it can be treated whole.

Sodium hydroxide (caustic soda) is added at a rate of 3-4%. This disrupts the coating on the grain, which allows for direct feeding to cattle.

This can be done through a feeder wagon/mixer. Caution must be exercised as this is a hazardous material. One advantage is that it can be stored uncovered below a roof; there is no need to try to eliminate air.


In most cases this process involves mixing the grain with ‘feed grade’ urea. The purpose being to eliminate toxins, allowing for safe storage in a clamp.

Grain is best treated after being rolled. This process can lead to an increase in protein content of the grain of between 14-16%, however nutritional advice is required to properly calculate inclusion rates for animal feed rations.

There are many urea/ammonia-based products on the market to facilitate this process.

Some of these already have the urease enzyme included, so do not require additional urease to be mixed in. Most, however, operate best to a maximum grain moisture content of 20%.

With harvesting underway at present, growers are advised to speak to suppliers as early as possible to decide the best way to manage their grain.