Olives & Olive Oil Quality evaluation
Indications of Table Olive Quality
While there are internationally agreed standards by which the taste of olive oil is judged, no such standard exists for table olives. The only standards determined by the International Olive Council (IOC) concern physical defects that mainly affect the appearance of the product. The appearance may vary widely; even whether the fruit is green or black may depend on the cultivar, the maturity of the fruit and the processing method.
Nevertheless, there are some widely recognized guidelines concerning aroma, taste and texture. These three characteristics constitute what are called organoleptic properties, which determine the eating quality of the olive.
Olfactory properties (smell or aroma)
This should be clean and free from off odours. The precise characteristics depend on the type of processing that was applied. Much of the aroma of processed olives is likely to arise from fermentation.
Gustatory properties (taste or flavour)
While taste is somewhat subjective, there is some degree of consensus among consumers with more experience of olives. Consumers unused to olives tend to like mild-tasting olives, whereas a fuller characteristic olive flavour is often preferred by those whose tastes are more developed. The desired taste needs to balance the fruity flavour with the lactic acid found naturally in olives and with the pickling ingredients (salt and vinegar). Usually, acids produced by fermentation are experienced as more pleasant and integrated with the fruit flavour than acids which are subsequently added.
Tactile properties (texture)
Olives should be moderately firm, but not woody, and without tough skin or flesh. The flesh should separate rather easily from the fruit’s pit. Many variables can influence texture, but the main variables are the cultivar and the maturity of the fruit at harvest. The basic texture can then be altered either positively or negatively by processing.
The best course for a buyer is to be aware of these factors, but experience as many kinds of table olives as possible to develop his or her own taste preferences. There are hundreds of kinds of table olives on the global market, though many of them are restricted to certain regions. With this vast array of choice, there is no need to accustom oneself to one particular variety which may not be of first-rate quality. In South Africa, consumer tastes have become considerably more discerning in recent years. This has been a boon to the local industry, which is better known for excellent quality than for low prices or high production.
Indications of Olive oil Quality
The International Olive Council (IOC) has laid down strict standards concerning the laboratory and taste (organoleptic) attributes of olive oil. More recently, a freshness test was also introduced. The most basic, widely acknowledged criterion for high quality is that the oil should be cold-pressed extra virgin oil. To qualify as extra virgin, the IOC specifies there must be at least some fruitiness and no specified defects, with less than 0.8% free fatty acids. Unfortunately, not all olive oil that carries the label “extra virgin” conforms to this standard. This is may be due to fraudulent labelling or adulteration, or simply because the labelling standards of a particular country are not as stringent as those proposed by the IOC.
The IOC has also established some more detailed criteria for what is desirable in the flavour of olive oil. The standard positive and negative attributes are explained in the tables below. It should be noted that bitterness and pungency are not defects and tend to mellow as oil ages.
|Fruity||A spicy, fruit-like flavour indicating the use of undamaged, fresh olives. The exact flavour varies by cultivar and may include grassy and herbaceous flavours in green oils and floral, aromatic or buttery flavours in oil from ripe fruit.|
|Bitter||Acrid on the tongue. Typical of unripe olives.|
|Pungent||Peppery, sharp sensation in certain cultivars and oil from unripe fruit, perceived in the throat.|
Origin or characteristic taste
|Fusty||From olives that have undergone long anaerobic fermentation, usually from being stored in piles|
|Musty / Humid||Mouldy flavour from oil stored in humid conditions, from fungal or yeast growth|
|Muddy sediment||Oil left in contact with vat or tank sediment|
|Winey / Vinegary||From aerobic fermentation leading to the presence of alcohol and acetic (vinegar) acid|
|Rancid||From oxidation and other degenerative processes, with flavours reminiscent of solvent-containing materials such as wax, varnish or putty|
|Heated / Burnt||Oil “cooked” by excessive heating|
|Hay / Woody||From olives that have been dried out or frozen|
|Greasy||Like diesel or mineral oils or grease|
|Vegetable water (“fruit water”)||Oil left in contact with non-oil olive juice|
|Briny||From olives preserved in brine|
|Earthy||From olives unwashed after contact with soil or mud|
Table Olive Processing
Table olives need to be processed, as the raw product contains a substance known as olueropein, which makes it so bitter as to be inedible. This is done by one of five curing methods: dry-curing, oil-curing, water-curing, brine-curing or lye-curing, each of which involves covering the olives in salt or liquid.
Dry-curing involves packing olives in salt. In oil-curing, they are kept first in salt and then in oil. In water-curing, the olives are kept in water for a number of weeks. This method is less effective in reducing bitterness than brine- and lye-curing. Brine-curing, where the olives are submerged in a salt solution, can take months. The olives ferment during this time, so that sugars often change into acetic acid or lactic acid and flavours and nutrient composition change considerably. Greek and Sicilian style olives in brine are two typical products in this category.
The final method, lye-curing, uses an alkaline solution of potassium hydroxide or sodium hydroxide. Usually, several steps of curing – up to five – are needed. In the first step, the skin and outer fleshy part are cured and the lye solution is drained away. Subsequent steps progressively cure deeper layers of the olive pulp until all the flesh has been cured. Spanish style green olives typically go through this process, as do canned “black” olives that get their colour not from their maturity, but from oxygen added to the lye solution.
Olive Oil Production
Producing good olive oil requires olives that have been carefully harvested to avoid breaking the skin. Ideally, fruit is graded by quality before being processed separately. Olives usually pass through a vibrating screen, where a blower uses air to remove debris. They are only washed if they have been exposed to soil or spray residue, because any moisture can reduce the efficiency of oil extraction by creating water-oil emulsions, and it reduces the desirable fruity quality of the final product.
Stone mills or hammer mills are used to crush the olives to release the oil, usually together with the pit. Stone mills are now used comparatively seldom because they are inefficient and slow. Hammer mills throw the fruit against a metal screen by rotation. They are far more cost-effective than stone mills, but cause more emulsification and heating.
The resulting paste then goes through a process called malaxation. The paste is stirred to mix it and creates larger oil droplets, reducing emulsification, to make the oil easier to separate. The temperature is carefully controlled to ensure that the oil properties make it easier to extract without harming the taste. A recent trend in preserving the flavour of the paste at this stage is excluding oxygen by using nitrogen flooding or a special vacuum tank.
The oil is then extracted by one of several methods. The most traditional method is using a conventional olive press to remove the liquid component of the paste. More modern systems use centrifugal decanters or vertical centrifuges. One further method, the sineola process, is used. However, while the sineola process has certain advantages, such as retaining more nutrients, it tends to have low extraction efficiencies, so that a centrifugal process must be used to remove the remaining oil from the paste.
After the extraction of the oil, the remaining components of the paste must be managed and the oil bulk-stored for between one and three months. This will cause the remaining fruit-water and solid sediments to settle so that they can be removed. If this is not done, off flavours may develop in the bottled oil in a short time, shortening the shelf life of the product.