Some typical off-flavors faced in dairy industry

Good quality milk should have a pleasantly sweet and clean flavor with no distinct aftertaste.

Milk, however, is a delicate food that is often mishandled resulting off-flavors. These can cause severe difficulties to all parties in the dairy chain.

Retailers and light-induced off-flavors in milk

One of the most common off-flavors retailers face is a burnt feathers or hair flavor. This defect develops in milk as a result of its exposure to sunlight as well as fluorescent lighting. Especially bulbs with wavelengths below 620 nm.

Light initiates a chemical reaction in milk with proteins and fats. Certain vitamins are also susceptible to light-induced degradation like riboflavin and vitamin A. Exposure to sunlight for as little as 10-15 minutes is sufficient to cause the defect, while longer exposure times are generally required for fluorescent lighting. The closer the milk is to the fluorescent light source or the more intense the light, the quicker the development of the off-flavor (within 1-2 hours in some cases).

In general, the defect is more common in milk packaged in transparent plastic or glass, although it can also occur in milk in more opaque containers with very intense light and sufficient exposure time.

Preventing light-oxidized defects in milk involves simply protecting the milk from light, especially sunlight, and especially milk packaged in transparent plastic or glass. A few minutes exposure to the sun on a loading dock or during consumer transport may be all it takes.

Recommendations for dairy plants and stores include:

1. Milk receiving and handling areas, storage coolers, and display cases should be designed for minimum direct light exposure
2. Facilitate product rotation
3. Do not stack milk crates in storage in close proximity to over-head lighting, or use a cover
4. No light bulbs are in close proximity to the product at display cases
5. Fluorescent light bulbs used for display cases and coolers should be the “warm white” variety, which generally have less harmful energy in the critical wavelengths than the “cool white” variety.
6. Yellow shielding (e.g., over or in front of fluorescent bulbs) may be used to reduce the intensity of light.
7. Turn off unnecessary lighting in coolers and display cases during the night shift or when store is closed.
8. Light block additives or over-wraps may be used for some packaging material to help protect the milk. These materials may not offer 100% protection, so protection from light is still warranted.

Manufacturer and “cooked” off-flavors

UHT (ultra high temperature) processing ends up forming a variety of volatile compounds derived from the milk. Some of them contribute to specific undesirable flavor notes.

The “cooked” flavor of UHT milk comes from variety of sulphur containing compounds. The “stale” flavor, however, forms as these sulphur volatiles dissolve and both methyl ketones and aliphatic aldehydes increase over time.

It must be said, however, that the extent how individual volatiles contribute to the overall flavor of UHT milk is still unclear.

Potential means to remove or decrease these undesirable flavors and improve the consumer acceptability are:

1. The use of drop in additives
2. Active packaging

Product developer and fortified dairy products

Fortification – in simple words adding some minerals such as calcium and iron and vitamins to milk – is one way to develop innovative new products. Iron fortification of milk and dairy products is also considered as a potential approach to prevent mineral deficiency in mans.

Iron, however, is known to catalyze lipid oxidation. Fortification with FeCl3, FeSO4 or ferric/ferrous ammonium sulfate causes rancidity with development of an unpleasant odor and flavor.

There are different possibilities to avoid oxidized and metallic flavors and color changes.

1. Iron-enriched whole milk shows that ferric iron compounds cause rancid flavor when milk is pasteurized at temperature below 79°C. This off-flavor is acceptable, or completely eliminated simply by pasteurizing at 81°C.
2. Ferrous compounds normally cause definite oxidized flavor when added to raw whole milk before pasteurization. However, de-aerating the milk before adding the iron markedly reduces this off-flavor.

Packaging supplier and petroleum-like taints

Ethylbenzene occurs in nature as a fraction of petroleum. It is also an important synthetic chemical that is produced in large quantities as a precursor for styrene and polystyrene.

Since traces of residual ethylbenzene might be present in polystyrene, it cannot be excluded that during food contact ethylbenzene may migrate into food from polystyrene packaging material.

It is common to all milk products, especially cheese.

Farmers and few common (and funny) off-flavors

Milk readily absorbs odors to which it may be exposed. Unclean off-flavors may also be described or referred to as “cowy” or “barny”. They are those objectionable off-flavors that are associated with unsanitary farm conditions. A cowy or barny flavor may be common in areas where cows are housed during the winter months. A cowy flavor is also present in milk from cows with ketosis (a fairly common disease of dairy cattle), a condition in which there are traces of acetone in the milk and body fluids.

You would not expect, but one of the most common offenders of milk are wild onions, garlic, and related plants, which import a distinctive “flavor note” that is quite familiar to most people. These weeds grow particularly well during the rainy spring and fall seasons, though in some geographic regions they may be encountered at any time. Weed off-flavors may be encountered in milk, cream, butter, and fermented products.

Building constructor also responsible for taints

Defective building materials, particularly flooring materials can elucidate volatile compounds that are absorbed to dairy products. A few years ago a small independent organisation proposed to manufacture hand-made milk chocolates in premises that had previously been used for retail and storage purposes.

Before installation of the equipment, it was necessary to refurbish the building and a part of this involved laying a totally new floor. Soon after the first batches of chocolates had been produced, it was noticed that they suffered from a taint variously described as ‘like paint, paraffin or white spirit’.

A site visit from flavor scientists revealed that the damp-proof course under the new layer of concrete had a strong smell that was reminiscent of the taint in the chocolate. Subsequent analysis on the atmosphere close to the floor confirmed that a fault in the damp proofing was the most likely cause of that taint.