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The use of vegetables

asparagus with hollandaise

Nutritional Value of Vegetables

green peppers


Why is there so much attention to nitrate in food?     Nitrate is of nutritional value for the plants and is not poisonous.  However by storing nitrate rich foods or in the human body, it can be converted into the dangerous substance nitrite.
Nitrite hinders for example the provision of oxygen in the body.  Nitrite can also connect with particles from protein retaining food.  This connection is called nitrosamines, which can induce illnesses. Nitrate is only however only dangerous when taken in high doses. 
The average amount of nitrate consumed via food per day in Holland is around 110 à 160 mg.  About 80% of this is from vegetables.  The rest comes from drinking water and the drinks made from it such as tea and coffee.  Certain vegetables contain more nitrate than others such as endive, celery, Chinese cabbage, turnip, beetroot, and all types of lettuce, spinach, fennel and cabbage.

Some practical tips:

  1. Use various types of vegetables.  Vary nitrate rich vegetables such as lettuce and endive with other vegetables low in nitrate.
  2. Do not use the cooking liquid from nitrate rich vegetables to make soups or sauces.  The cooking liquid absorbs a certain amount of the nitrate.
  3. Do not store leftover cooked vegetables rich in nitrate.

Oxalic acid

There are foods that can reduce the absorption of calcium in the body.  Oxalic acid for example is present in spinach, rhubarb and French beans.  Oxalic acid particles join up with calcium particles to form a substance that cannot be dissolved in water and which cannot be absorbed through the wall of the intestines.  Calcium can therefore not be absorbed into the body.   Serious shortages of calcium do not however often occur.

Purchasing vegetables

When vegetables are being purchased the following points should be taken into careful consideration:

  1. The choice of vegetables that can be bought
  2. The condition of the vegetables
  3. The quality of the vegetables
  4. The price of the vegetables

The large variety of readily available vegetables nowadays can be divided into various groups.



a. Cabbages

White, red, Savoy, pointed, Chinese

b. Leafy vegetables

Lettuce, endive, spinach

c. Fruit-vegetables are 3 main groups:

  1. leguminous green vegetables
  2. Cucumber types
  3. Fruits of the nightshade family


French and runner beans, peas
Cucumber, courgettes and gherkins
Tomato, paprika, peppers and aubergine

d. Bulbs and roots

Carrot, beetroot, parsnips, onions

e. Stems and shoots

Celery, hop

f. Onion varieties

Leek, garlic, chives

The choice of vegetables on the market

Each group of vegetables will be discussed individually in the following paragraphs.

    1. Cabbages

All the well-known types of cabbage belong to the Brassicaceae (cabbage) family, as do radishes, broccoli and turnip leaves.  The most important cabbage group is the so-called winter cabbages such as red cabbage, yellow and green Savoy cabbages, January King (which has leaves with a purple tinge, round cabbage with green outer leaves but is good for coleslaw.)  The winter cabbages are compact and closed compared to the more open varieties such as Chinese or pak choi which are looser and where the leaves and stems are also eaten.  Brussels sprouts are very small cabbages.  Other “Brassica” (cabbage varieties) are cauliflower, broccoli, wintergreens, turnip and Swedes.

broccoli brussel sprouts
    1. Leafy vegetables

Leafy vegetables are plants where principally only the leaf is eaten, for example lettuce, endive, spinach, green and red chicory.   They can be eaten both raw and cooked.  The colour of the leaves varies from pale yellow to dark green.  Sometimes the cell juices contain the pigment anthocyan which colours the leaves red.  Leafy vegetables such as spinach, sorrel, and endive dry out very quickly and wilt.


    1. Fruit-vegetables

The skin of this type of vegetables must be perfect and shiny.  Various bacteria and fungi can cause decay.   The first signs of deterioration can be seen as areas of discolouration on the skin.  The vegetables will become soft and begin to rot.
Fruit-vegetables can be divided into three categories: leguminous green vegetables, cucumber types and fruits.

Leguminous green vegetables are crops where the seeds are formed in pods or tubes.   Several varieties such as French beans, mange-tout (snow peas) and runner beans can be eaten whole, unlike peas and broad beans, which are podded (the seeds removed and eaten and the tubes disposed of).
Leguminous vegetables must have perfect skins – on French beans and runner beans a grey/brown discolouring can be caused by exposure to damp.  In the main section on beans, later in the chapter, attention will be given to vegetables where only the seeds are eaten and dried vegetable seeds.   Naturally the purchase and storage and quality of these products are very different to those of fresh vegetables.

aubergine green beans

Cucumber or pumpkin types of vegetables are recognizable by their shape, which is either elongated or round.  These vegetables are covered with a skin.  Examples are pumpkins, cucumbers, courgettes and gherkins.

Fruits, also known as the nightshade family are for example tomatoes, paprikas, aubergines, and Spanish peppers.  They are round or elongated and the seeds all form in the centre.

d.   Bulbs and roots

Bulbs such as potatoes, beetroot and fennel are recognizable by their bulb shapes.  Root vegetables such as carrots, winter radish and salsify are recognizable by their pen shapes.
All of the bulb and root vegetables are grown under ground. Examples with side shoots or ones that have burst do not satisfy the quality required of them. Roots from plants that have turned to seed in general become woody and not suitable for consumption.  Decay of bulb and root vegetables can be seen in discolouring and rotting due to fungi and bacteria.

e. Stem and shoot vegetables

Examples of stem vegetables are kohlrabi, celery, fennel and rhubarb.  Examples of shoot vegetables are asparagus, hop, bamboo shoots and taugé.
Strictly speaking they do not belong together but since the stems are all eaten, for convenience they form one group in this book.   The stems can be grown above or under the ground.     If they are allowed to dry out they become tough and fibrous.  Decay in these vegetables can be seen normally in the appearance of grey fungus, yellowing of the leaves or general rotting.

asparagus celery
    1. Onion crops

Onion crops such as onion, garlic, leek and chives are recognizable by their round or elongated shapes.
The green parts of these vegetables must be fresh green in colour and crisp. Fully-grown onions should be firm to the touch.  The dried skin should have not more than a few small tears.  Pressing the thumb at the point where it has been cut from the plant – it should be fine and firm can test onions.   If it is soft, it has a fungus and will decay quickly.

leeks onions
  1. The condition of the vegetables

The conditions of the vegetables discussed in this chapter are as follows:

    1. Fresh raw vegetables
    2. Cool-fresh vegetables
    3. Preserved vegetables
  1. Fresh raw vegetables

Fresh raw vegetables are vegetables that have not undergone any preparation process prior to purchasing for example whole white cabbage or raw beetroot.

  1. Cool- fresh, vegetables

Cool-fresh vegetables are vegetables that have been prepared inn advance of purchasing.  Depending on the product these vegetables can be cleaned and/or sliced.   The packaging of these vegetables can determine their shelf life.
Compare for example:

  1. Cleaned and washed runner beans unpacked in a cool vitrine
  2. The same product in a vacuum packed plastic box
  3. Lettuce, washed and packed with a combination of oxygen and nitrogen

All of these products fall into the category of cool-fresh vegetables, however their shelf life is not the same.

  1. Preserved  vegetables

Preserved vegetables are vegetables that have been treated to improve their shelf life by the manufacturers / suppliers.
Examples are as follows:

  1. Vegetables in pots or tins (pasteurised or sterilised) such as peas, broad beans or beans in tomato sauce.
  2. Freeze-dried vegetables such as leek, celery and onions.
  3. Deep frozen vegetables such as carrots, spinach, cauliflower and red cabbage
  4. Dried vegetables such as peas, marrowfat peas (capucijners) and brown beans
  5. Vegetables pickled in vinegar such as silver onions and gherkins
  6. Fermented vegetables such as sauerkraut
  7. Sous-vide prepared vegetables such as asparagus

canned beans

  1. The quality of the vegetables

When purchasing vegetables special attention should be taken that the quality meets the (high) requirements of the kitchen.

  1. They must be whole and healthy - unblemished  (caused by rotting)

-     They must not be damp on the outside

  1. They must be free of soil and dirt
  2. They must have the normal shape, colour and flavour for the particular crop
  3. They must be sufficiently ripe to allow for further preparation
  4. They must not contain any materials dangerous for human consumption
  5. They must not have been damaged by vermin
  6. They should be as free as possible from parasites or damage by parasites

These basic requirements are based on Dutch and European quality standards.
The Dutch standards that are not based on European quality standards are only applicable to products from Dutch origin.
Quality standards are broken down into four quality classes for fruit and vegetables.

Class Extra Quality (or super quality):  As the name suggests, fruit and vegetables in this class must be perfect.

Class 1:  The products in class 1 must be of good quality.  Small blemishes in shape and colour and small imperfections on the skin are permitted.

Class 2:  The products in class 2 must be reasonable and slightly more imperfections are permissible than in class 1.  Blemishes in shape and colour, a rougher skin, and blemishes that have closed again are permitted.

Class 3:  The products that are permitted on the market in class 3 are broccoli, Chinese cabbage, cabbage, celeriac, fennel, turnip and pak choi.   Other products in class 3 are often used in industry.

The classification of products into quality classes has a number of advantages:

  1. A clear division is made between the various qualities of fruit and vegetables on the market
  2. A better quality product can demand a higher price (better for the growers)
  3. It is easier to choose the quality required for a particular purpose
  4. Products from home and abroad are assessed on the same scale
  5. Quality control is carried out in a uniform manner as far as possible

During the quality control of vegetables they are checked for size and weight. Random checks are also carried out on the quality of the centre of products – by cutting them in half.  The flavour of the products does not play a direct roll at this stage although they may not have any strange aromas.
It is possible that vegetables that may look healthy and whole on the outside are not as good as they look when cut through.   They may not be fit for human consumption after-all. 
Bulbs, root and fleshy-fruit vegetables can be subject to internal defects and cause disappointment.

The following two defects are not uncommon in vegetables:  drying-out and discolouring.

When a product is dried out, the inside is like a sponge. This can occur in bulb varieties where the root/and or the stem flesh has thickened.  Products that are dried out have less flavour and become tough.  This is caused by water being extracted through the leaves which carries on after the crop has been harvested, especially if the products are stored in a dry storage.  Radish is very susceptible to drying out although there are huge variations between the varieties.  Turnip is also very sensitive to drying-out.

Vegetables can discolour in various degrees for many reasons.  Celeriac is discoloured by a lack of borium (these are spore elements that the celeriac absorbs from the soil).This leaves the celeriac with brown, spongy props and unfit for use.

Flavour and taste
The taste and flavour of the vegetables play an important part in judging the quality of them. Where the vegetables are grown can influence how they taste whereas their flavour is influenced by the essential oils contained in the plants.  There can therefore be large variations in flavour and taste.
Other important factors that can influence the taste and flavour include temperature, light, fertilisers, the time of harvesting and in general the manner of production.  Products from countries where the temperature is warm and dry often taste better and more aromatic than when produced in countries with a cooler and wetter climate.  Products grown in natural (outside) conditions take longer to grow and ripen and therefore often taste better than vegetables grown in a greenhouse.  A slower ripening process in combination with environmental friendly production methods will result in products that are tastier and fuller of flavour.
When products are harvested while not fully ripened they are not normally as full of flavour as they would be if allowed to ripen.  For example if spinach which has been thinly sowed is allowed to grow fully, the rather course leaves will have far more flavour than spinach sowed densely and harvested while the leaves are still young.

  1. The price of vegetables

The price of vegetables depends on the availability and condition (quality).  Due to the various production methods, vegetables are often readily available the whole year round.  Each type of vegetable has quality controls for the specific sort and can be divided into (very) high quality categories downwards.  This will naturally have influence on the price.  In chapter 6 the availability throughout the year of the various vegetables will be discussed.  In general the price of vegetables is lower when they are at their peak in season.  The price of vegetables is often higher when the demand for the products rises for example over the Christmas period or other national holidays.


Handling vegetables in the kitchen

The handling of vegetables varies with each different situation.  The following facts are important when dealing with vegetables on a daily bases:

  1. The delivery of the vegetables
  2. The storage of the vegetables
  3. The preparation of the vegetables
  4. The cooking of the vegetables
  1. The delivery of the vegetables

When fresh, cool-fresh and preserved vegetables are delivered, it is important to control the following points:

  1. Check that the vegetables that are delivered are in fact the vegetables that were ordered
  2. Check that the temperature of the vegetables is correct
  3. Check that the amount delivered is the same as the amount ordered
  4. Check that the packaging is not damaged
  5. Check the sell-by dates
  1. The storage of the vegetables

Differences in storage and transport are made between the various types of vegetables:

    1. Fresh vegetables
    2. Cool-fresh vegetables
    3. Preserved vegetables
    1. Fresh vegetables

Cabbage types
Fresh cabbages can be stored at temperatures between –0,5º to ± 0,5º C.  If the temperature is lower there is a danger that leaves will freeze around their outer edges, which will result in them, becoming brown and smelling rotten.

Leaves, stems and shoots
The best temperature for leaves and stem vegetables is between   0º and 1ºC. At this temperature they can be stored the longest.  For leafy vegetables an optimal relatively high humidity of 90 to 98% is best.  The high humidity will ensure that the leaves do not dry out quickly.

Leguminous green vegetables
Depending on the type, leguminous vegetables can be stored at temperatures between 0º
and 6º C. French beans, runner beans and butter beans are best stored at 6º C.
  Peas, snow peas and broad beans are best stored at a temperature of 0º to 1º C.  The optimal relative humidity for all the leguminous vegetables is 90 to 95%.  If they are stored at temperatures above 6º C, they will quickly deteriorate.  They will become a grey-whitish colour, wrinkle and become tough.

Cucumber types
Cucumber types are best stored at slightly higher temperatures between 7º and 13º C.  If they temperature is too low these vegetables will deteriorate quickly. Again the optimal relative humidity for these vegetables is between 90 and 95%.

Bulbs and root vegetables
Bulbs and root vegetables are best stored at a temperature of 0º to 1º C.  The optimal relative humidity is between 90 and 98%.  They are best protected against drying-out by being stored in plastic foil or boxes.

Onion types
All types of onions should be well dried after harvesting.  This is important to improve their shelf life.  If onions are damp when purchased they can become glazed.  Once dried properly they are best stored at a temperature around freezing point 0º and -1º C.  The relative humidity should not be higher than 85%.

    1. Cool-fresh vegetables

As the name suggests, cool-fresh vegetables must be placed immediately after delivery in the cooling till they are required for further use.

    1. Preserved vegetables

The following tips should be noted for the storage of preserved vegetables:

  1. Store pasteurised or sterilised vegetables in a cool, dry and dark storage area.  Do not store them longer than their sell-by-date.  Do not store opened pasteurised vegetables in their original tins or pots, rather in stainless steel or synthetic containers to avoid discolouring and deterioration of flavour.
  2. Freeze-dried vegetables must be stored in a cool store and not kept longer than their sell-by-date (clearly identifiable on the sticker).
  3. Deep frozen vegetables should be stored at a minimal temperature of -18º C.  The length of storage is dependent on the type of vegetable.
  4. Dried vegetables should be stored in a cool, dark area.  It is possible to store dried vegetables indefinitely if they are stored optimally.
  5. Pickled vegetables should be treated with the same criteria as vegetables in jars or tins
  1. The preparation of vegetables 

When preparing fresh vegetables the following points must be taken into consideration:

  1. Wash the vegetables as quickly as possible.  This is very important as vitamin C dissolves in water.
  2. Wash the vegetables as far as possible before cutting them in cold water around 2 - 4º C.
  3. Do not cut the vegetables finer than necessary to avoid losing valuable vitamins
  4. Do not allow the cut vegetables to stand in water longer than is necessary

Cool-fresh vegetables and preserved vegetables have already been cleaned and sliced or cut.  These vegetables are ready for direct consumption or direct use for an end product.

  1. The cooking of vegetables

When cooking vegetables there are several rules and guidelines that should be observed.  These rules are applicable to fresh, cool-fresh and preserved vegetables.  Some minerals and vitamins dissolve in water.  Especially vitamin C cannot tolerate heat.  To avoid these valuable vitamins being lost, it is important to take the following into careful consideration:

  1. Wash the vegetables before chopping and cutting
  2. Allow the chopped vegetables to stand in water for as long as it takes to remove and soil only.
  3. Cook the vegetables with as little water as possible and as quickly as possible. Vegetables with a lot of tough fibres require more cooking time than vegetables with few or soft fibres.
  4. Do not stir cooking vegetables more than is required
  5. Use the cooking liquid where possible (only those low in nitrate) for soups or sauces as the cooking liquid contains vitamins and minerals.
  6. Serve the vegetables as quickly as possible to avoid loss of freshness, colour and vitamins.


The method of preparation and cooking is dependent on the structure and type of vegetable.  Vegetables with a strong structure such as cabbage contain tough fibres and require longer cooking times than vegetables with a fine structure such as lettuce.



Cooking technique


White cabbage




Red cabbage




Pak choi






Normally not cooked






Iceberg lettuce




A few rules for cooking preserved vegetables:

  1. Heat tinned and potted vegetables quickly in their preserving liquid
  2. Cook deep-freeze vegetables straight from the freezer (not defrosted)
  3. Use little or no liquid with leafy vegetables
  4. Cook dried vegetables in the same way as fresh vegetables

The cultivation of vegetables

Two distinctions are made in the cultivation and methods of cultivation of vegetables:

Types of cultivation:

  1. Full ground (outdoor)
  2. Greenhous

Methods of cultivation:

  1. Controlled or integrated cultivation
  2. Biological (organic)

In the cultivation of vegetables in the full ground (outdoors), the products are not protected against the weather.  This means that the quality of the products and the yield are dependent on the weather conditions.  Products suitable for cultivation outdoors are the cabbage types, roots and bulbs and robust vegetables such as endive and leeks.
Normally two harvests a year can be made from the full ground.  Protection is not normally given to the crops.   Products harvested from the full ground are seasonal vegetables.

In the greenhouse the cultivation is knows as controlled cultivation.  The influence of the weather is less important to the growing process and there can be up to five crops harvested per year.
Since the temperature is controlled the vegetables do not only grow at the same rate, but it is possible to introduce and grow tropical or subtropical specimens in colder climates.  The price of these vegetables is normally higher than of vegetables grown outdoors.


Both in the full ground and in greenhouses are vegetables cultivated organically or by the controlled/integrated method.

In the controlled/integrated method of cultivation, less use is made of chemical pesticides and artificial fertilisers than by the most commonly accepted cultivation methods (traditional methods).  It is expected that in the future in Europe, more and more growers will use this method of controlled/integrated cultivation.  It is at the moment a middle road between organic farmers and the traditional farmers who have overly used chemicals and artificial fertilisers in the past.

In organic farming the use of chemical pesticides and artificial fertilisers is strictly forbidden.


Hallmarks offer information and assurance about the manner in which products have been cultivated.  At the moment there are hallmarks for a number of cultivation methods.  In Holland the EKO hallmark on packaging assures the buyer that the product has been cultivated in an organic manner.
The organic cultivation method is more expensive than non-organic methods.  However gradually, despite the difference in price, more and more people are turning to environmentally friendly products.  These products are healthier, taste better and are closer to nature.

Illustration 4-1 The EKO hallmark

Environmental friendly production methods

Earlier in this chapter the outward, directly visible qualities of vegetables have been discussed.  As well as this however there are various characteristics that have influence on the quality of the vegetables that are not seen with the naked eye.  In the 1960’s farmers began to strive for a larger crop yield and paid less attention at that time to the quality of the crop itself.  The crops were often over sprayed with pesticides against diseases and plagues. 
By the 1980’s however it had become apparent that there were grave consequences for the environment if this intensive spraying were to continue.  The accent began to shift away from the size of the crops back to the quality and the possibility of guaranteeing quality crops.   This tendency towards environment friendly products continues and hopefully will remain the way in the future.

Regularly articles are published concerning poison scandals, soil and water pollution and acid rain.  The results are that society has started to question the risks of eating food cultivated in the “traditional” style.  The chances in Holland of eating traces of pesticides are very small.  Chemical substances that breakdown slowly are almost all substituted for substances that breakdown more quickly and do not leave traces of their spores in the product.  Farmers must also adhere to the regulations of not harvesting the crops after the last spraying for a safe period of time.

In greenhouse cultivation various diseases and plagues are treated by exposing the diseases to there natural enemies in other words in an organic manner.  Nowadays in outside cultivation far more thought is also put into the intensity of spraying and cutting back the concentrations. 
However it is important to wash vegetables and fruit thoroughly before use and to peel bulbs carefully.
“Organic or biological production” means that the grower has used responsible organic production methods.  To try to stimulate these production methods and control them, an organisation for organic production methods has been created (called SKAL in Holland).

Organic production means durable, sustainable production. The public law on SKAL – norms for vegetables is based on EG regulations.  The regulations are included in the Dutch Agricultural Quality Laws.  In these regulations there are guidelines for:

  1. The production of food, physiologically high qualitative, in sufficient amounts, without traces of dangerous materials for humans and animals
  2. The retention or improvement of an optimal soil fertility
  3. The retention or improvement of nature and landscape
  4. The retention of as many species as possible
  5. The reduction of all the influences that harm or cause danger to the environment such as chemicals
  6. The minimal use of natural materials that can become extinct such as oil

In general these aims can be met by:

  • Ensuring a living, fertile soil
  • Carrying out  preventative crop protection by for example cultural changes, crop rotation, crop and variety choices
  • Fertilising with organic fertiliser, green fertilisers and natural minerals
  • Weed killing with the use of mechanical aids
  • As little as possible use of chemical-synthetic fertilisers and artificial fertilisers
  • The reduction of additives of growth materials and hormones in animal feed
  • The reduction of industrial production systems such as those carried out in the bio-industry