The Economics of Damage and Bruising Prevention

Potato bruising is a serious problem in potato production worldwide. Damaged potatoes going into storage can cause deterioration of the entire crop. Potatoes bruised during handling operations will be rejected by processors looking for perfect material to make perfect potato products. Estimates indicate that more than 60% of some crops are damaged in some way which leads to financial losses running into Billions and a massive waste of crop. The effects of such losses to any potato-related business cannot be over-estimated.

Reducing Damage and Bruising

Achieving the highest quality in all types of harvesting conditions can be difficult, but mist spraying has been shown to reduce bruising, particularly in dry conditions when dolmen rollers tend to cause potatoes to bounce.

The fine mist spray from the nozzles in a spray bar positioned over the rollers dampens both the potatoes and the rollers in the harvester. This lubricates the movement of the potatoes over the rollers and helps to prevent them being pinched and damaged.

Lifting conditions can be highly variable, so a misting unit such as the Harvester Mister should be standard equipment fitted to all harvesters in all conditions.

Martin Lishman harvester mister mounted on potato harvester
Martin Lishman’s Harvester Mister bolts to the harvester to provide a fine mist spray over rollers

Monitoring Damage and Bruising

The huge potential losses caused by bruising isa clear incentive for growers and processors to monitor bruising, take preventive action and reduce their losses. If the solution is economical in relation to the size of the losses, it should be grasped with both hands. An example of this is an electronic potato, such as the TuberLog. If this is used regularly bruising problems caused by poor machine maintenance or incorrect settings can be detected quickly before more damage takes place. Machine settings are often changed, but the effects on bruising may not be realised. A quick check with an electronic potato can help to ensure bruise-free working and provide peace of mind that quality standards are being maintained.

TuberLog is an impact sensor embedded in a synthetic shape that mimics the size, shape, density and movement characteristics of a typical ‘ware-sized’ potato. It records impacts while moving with real potatoes during harvesting and processing and locates damage and bruise-causing parts of machinery. The impacts are transmitted instantly by Bluetooth so the operator can immediately locate the impact source and change machine settings to reduce impact levels and minimise bruising.

The advantages of using an electronic potato will be clear to growers, producers and processors through an increased return on their investment in the potato crop and retention of key customers through the consistent supply of high quality potatoes. Manufacturers of harvesting and post-harvesting machinery can benefit by being able to demonstrate the quality levels of potatoes passing through their machines and assisting users to set them up for optimum performance. Machinery designs can also be improved by using an electronic potato to identify significant impacts levels. Agronomists and crop consultants often use an electronic potato to advise on the ideal machine settings for bruise-free production and to gather evidence for adherence to quality control procedures. On a broader front, research and development technicians can investigate materials and handling techniques that would reduce the risk of damage to potatoes and determine thresholds for the risk of damage due to impact force to potatoes of different varieties and different growing and storage conditions.

The TuberLog Electronic Potato is used to measure impact levels in all types of potato handling machinery

Assessing Potato Bruising

Different varieties or the same variety at different temperatures can bruise at different impact levels. When potatoes are bruised, the physical effects are not immediately visible. A biochemical reaction takes place which gradually causes a colour change at the point of impact. In cool dry conditions this effect can take several days to appear.

A potato hot box is designed to speed up this reaction time by creating warm, damp conditions for bruise development to occur more quickly. Optimum bruise development is at 30°C and 97% RH for 12 hours. If bruise testing using a hot box is used in conjunction with an electronic potato, the impacts measured with the electronic potato during harvesting or grading can effectively be calibrated by relating them to the level of bruising that occurs in a hot box. This allows action to be taken sooner, resulting in fewer bruised and damaged potatoes. 

Martin Lishman’s hotbox reveals bruising in just 12 hours

Quality Control for Stored Potatoes

Before storing potatoes, it is important to know the eventual market and the specifications required of that market. Specifications will depend on a range of quality measures such as skin finish, dry matter, fry colour and sugar content. Crops should be assessed in relation to these parameters, both before and during storage. Inevitably, the presence of rots and diseases or damage caused by bruising will have a significant effect on both the storage outcome and the ability to meet customer specifications.

Quality Control is an investment. Initial inspection of loads should include use of a hot box to check for bruising damage and the presence of rots. This will determine if the loads can be safely taken into storage. Once in the store, monthly monitoring of factors that are likely to change, such as sprouting, rots, fry colour and certain blemish diseases should be carried out.

Detecting diseases and rots before they become obvious is a significant challenge. Although a hot box can create very precise conditions of temperature and humidity, there is very little known about what precise combinations of these factors cause most rots and diseases to occur and which can be used to accelerate their occurrence before the potatoes go into storage. For example, It is known that pink rot thrives at 25°C and can take about 3 days to arise at this temperature, but the humidity level that encourages it and whether or not the occurrence can be speeded up are aspects that are unknown. The hot box provides a very useful tool to discover the missing information since many combinations of conditions can be tried over a short period of time, but this probably requires industry research funding to build up a data bank of such information for a wide range of rots and diseases.

Store and Tuber Temperature Monitoring

Accurate temperature monitoring of stored potatoes is critical for early warning of quality issues, preventing deterioration of product and maintaining correct storage temperatures for different markets. Crop temperatures should be as uniform as possible to minimise the risk of condensation. The more comprehensive and the more frequent that temperature monitoring takes place, the better the chances of good store management.

There are many systems available to do this, including basic measurement devices such as T-bar thermometers for measuring the internal temperature of individual tubers, permanently located rigid or cable temperature sensors designed for bulk or box stores and internet-based remote monitoring and automatic ventilation control systems. One such system is Barn Owl Wireless that, in addition to monitoring and logging temperatures 3-hourly in the crop and continuously for ambient temperature, and presenting the data in both graphical and tabular format, also provides the facility to link measurements to automatic equipment controls. The advantages this provides are a reduction in energy use compared to manual control methods, increased temperature control efficiency and the ability to fully manage stores remotely, without the need to manually operate equipment. 

In both box and bulk stores, sensors should be preferably located in the top and bottom of the stack, with most located in the top of the crop and some at the base. Readings should always be taken in the same places so that they show actual changes rather than location differences. 

Barn Owl Wireless gives a complete overview of the stores condition

Post-storage Quality Assessment

To avoid the problem of rejection on delivery, it is important to know the quality of product before it leaves the store. Tests may include dry matter, glucose and fry colour tests.

Dry matter content directly influences the yield of processed potatoes, the oil absorption rate in fried products and the texture of cooked potatoes. Dry matter is also used as an indicator of bruising risk, with high levels associated with more damage.

Dry matter varies between varieties, but dry matter of the same variety may also vary between seasons in the same locality. This can be the result of differences in the time of planting, soil moisture and ambient temperature.

The dry matter of potatoes can be calculated because extensive research work was carried out many years ago using oven tests which related the density or specific gravity of potatoes to their dry matter.

Hydrometers such as the Zeal and Weltech types use this relationship to display dry matter either on a paper scale or a display screen. They both rely on potatoes having negative buoyancy (they sink in water), which creates a contrast between the downward force of the potatoes in water and the upward force of the air in the hydrometer float or the weight in air of the potatoes in the case of the weigher.

Sugar content plays an essential part in the culinary and technological quality of potato tubers. It also depends on variety, maturity at harvesting and storage conditions. Measuring glucose levels, such as with the Glucolis Blue kit, can help to manage harvest times and storage temperatures to ensure precise colour control of crisping potatoes and French fries and determine the best time to move potatoes out of storage.

The Weltech Hydrometer provides quick and accurate dry matter results