Fresas

The Strawberry (Fragaria) belongs to the rose family (Rosaceae) and is one of the most popular summer fruits. There are more than twenty kinds of strawberry plants. Crossing strawberries from California, which have a hard fruit, with the softer European strawberries, resulted in sturdier varieties that could be exported over long distances.

Strawberries are so-called false fruits. The ovary, seed and bottom of the flower contribute to the fruit forming. A strawberry is a swollen receptacle of the strawberry flower with yellow seeds on the outside. The strawberry plant produces stolon or ‘runners’ to propagate itself.

Fresh strawberries are very healthy because they are rich in vitamin C and low in calories. The smaller the strawberry, the sweeter it tastes. Homegrown strawberries taste best, because strawberries will quickly lose their flavor because of the long supply lines.
Strawberries are often used as a flavor enhancer in for example yoghurt because of their strong aroma. Strawberries are also often made into jams. 

Canned Strawberries

Strawberries can be preserved by pasteurization and are sealed in a can or in a jar. After the harvest, the strawberries are sorted, washed and canned. During the canning process a syrup is added and after that the closed cans and jars will undergo a heat treatment.

The canned strawberries are different from strawberry jam. Strawberry jam is made by boiling the strawberries, sugar and a gelling agent, after which the mixture is put into jars and is pasteurized.

An alternative process to give strawberries a longer shelf life is freezing. By using the IQF method (individually quick frozen), the strawberries’ flavor and texture are better preserved. The final product is meant for frozen distribution.

A second alternative is pasteurizing the strawberries under pressure. Using this technique, the texture and flavor remain closest to that of fresh strawberries.

Syrup

Strawberries are put in syrup in order to preserve their taste. The syrup contains a mix of sugar and water, with the possible addition of glucose or glucose syrup.

Strawberries in syrup are divided into three classes:
- In light syrup: a sugar-content in the liquid part of 11% and a total of 18°Bx (Brix)
- In heavy syrup: a sugar-content in the liquid part of 13% and a total of 21°Bx
- Extra heavy syrup: a sugar-content in the liquid part of 15% and a total of 24°Bx

There are special varieties of strawberries used for industrial processing which easily let go of the green stem on top of the strawberry, also know as the crown. In addition, sturdy strawberries which are not too large, fully ripened, with an intense red color, good flavor and aroma are preferred.

Production process strawberries in syrup

Cultivation

Strawberries in the Netherlands are grown directly into the garden soil covered by plastic or glass. Strawberries can be grown in many types of soil, provided that the soil can retain sufficient water, contains humus and has a low pH. Materials to cover the soil, such as black plastics or straw ensure that there is less weed growth and enable the soil to retain the water better.

When the flower buds are removed from a strawberry plant, the plant will immediately switch to a vegetative state. This will create stolons (runners), which will develop into new young strawberry plants.

Because the strawberry plant is self-pollinating, there is no need for cross-pollination to take place. Wind and insects are crucial to the pollination process of the strawberry plant.

Normally, strawberries are planted in August, so they can be harvested the following year in June. Through acceleration of the growth process by covering the strawberries with perforated foil, straw or by using refrigerated plants the strawberry harvest can take place from late December to late February. The strawberries are harvested when they are not fully ripe yet, because they will ripe further after picking.
The strawberries are harvested by hand by taking the strawberry carefully and twisting the stem perpendicular to the strawberry, so it will break off. The strawberries are sorted immediately after picking.

Cooling

Processing of the strawberries is done in during the period from mid June to mid July. After harvesting, the strawberries must be processed or stored cold as quickly as possible. Strawberries are very sensitive to temperature and relative humidity, which both control the breathing activity, and thus have an impact on regulating the degradation of sugars and flavorings. A rapid development of micro-organisms can cause the consistency and structure of a strawberry to deteriorate. When strawberries are stored at a temperature between 0 and 5°C and kept in an area with a relative humidity of 90% they will expire within two days.

Sorting

Before the refrigerated strawberries are washed, the mouldy and rotten strawberries and contaminants are removed by sorters from a sorting belt. Strawberries that have not fully ripened yet are kept aside to later be processed to pulp.

Washing

After being carefully sorted using the sorter belt, the strawberries are transported to a Hermes Washer, or a so-called double washer. In this machine, the strawberries are presoaked, were with rising air bubbles sand and other contaminants, like the heat-resistant fungus Byssochlamys Fulva are removed. In order to make sure that the strawberries used for syrups do not contain more than 50 mg of sand per kg of the finished product, the strawberries are put on a mesh belt and washed down with water. After the cleaning the fruits are given time to drain. The process of washing the strawberries should not take too long, because it will make the the flesh of the strawberries soft making them fall apart easily. The water used for cleaning the strawberries should be of good quality and decontaminated with ultraviolet light or chlorine.

Canning

Before the strawberries are pasteurized they are put in cans. By using a filling table continuously vibrating cans are being filled up with strawberries. 550 to 700 grams of strawberries are needed to fill a container of a liter, so there will be sufficient strawberries left after the shrinking of the strawberries that happens during the pasteurization process. Subsequently, the content of the cans is put under a vacuum, to prevent unwanted oxidation reactions or deformations of the cans. After closing the vacuum pump, hot syrup is added. The concentration of the sugar solution depends on the type of syrup and the sugar-content of the strawberries. To lower the pH citric acid or lactic acid may be optionally added. Legally permitted food dyes can also be added. After the hot syrup is added the cans are sealed before pasteurization.

Pasteurize

The cans are pasteurized at a temperature between 85 and 95°C, to have a temperature of 80°C at the can’s core. After pasteurization, the cans are cooled down immediately to about 30°C. The high sugar content, low pH and pasteurizing contribute to complete conservation of the product.

Warehousing

The cans are labeled and packed in boxes, after which they can be stored for a long period of time outside of the refrigerator. 

Food Safety & Hygienic Design

On relatively acidic products (pH<4.6) microbial spores can not develop into vegetative (alive) micro-organisms, which could potentially spoil or severely contaminate a product. Sterilization or deactivation of spores is therefore unnecessary. The milder pasteurization technique is sufficient to kill vegetative cell and has less of an impact on the flavor.

The acidity of the strawberries can be critical. This is the reason that strawberries are put in heavy syrup.

The production equipment and machinery must be of of a GMP-class. This means that the machinery and equipment must be visibly clean before use. In case that the machinery cannot be emptied fully (and is clean and set aside dry), the machinery has to be thoroughly cleaned and disinfected before the production process can start again. Cleanable to a microbial level (hygienic design) is not necessarily required for this process. A light microbial contamination should not be a problem.

Even though the product undergoes a heat-treatment after being sealed, does this not give a license to clean less frequently or not fully clean the machinery and equipment. Large amounts of heat-stable toxins, originating from micro-organisms, can remain toxic even after pasteurization and will keep posing a threat to the health of the consumer.