What are yeasts and Moulds

Yeast are unicellular fungi. The precise classification is a field that uses the characteristics of the cell, ascospore and colony. Physiological characteristics are also used to identify species. One of the more well known characteristics is the ability to ferment sugars for the production of ethanol. Budding yeasts are true fungi of the phylum Ascomycetes, class Saccharomycetes (also called Hemiascomycetes). The true yeasts are separated into one main order Saccharomycetales.

Yeasts are characterized by a wide dispersion of natural habitats. Common on plant leaves and flowers, soil and salt water. Yeasts are also found on the skin surfaces and in the intestinal tracts of warm-blooded animals, where they may live symbiotically or as parasites. The common "yeast infection" is typically Candidiasis is caused by the yeast-like fungus Candida albicans. In addition to being the causative agent in vaginal yeast infections Candida is also a cause of diaper rash and thrush of the mouth and throat.

Yeasts multiply as single cells that divide by budding (eg Saccharomyces) or direct division (fission, eg. Schizosaccharomyces), or they may grow as simple irregular filaments (mycelium). In sexual reproduction most yeasts form asci, which contain up to eight haploid ascospores. These ascospores may fuse with adjoining nuclei and multiply through vegetative division or, as with certain yeasts, fuse folic acid.

In brewing, Saccharomyces carlsbergensis, named after the Carlsberg Brewery in Copenhagen, where it was first isolated in pure culture by Dr. Emil Christian Hansen (1842-1909) in 1883, is used in the production of several types of beers including lagers. S. carlsbergensis is used for bottom fermentation. S. cerevisiae used for the production of ales and conducts top fermentation, in which the yeast rise to the surface of the brewing vessel. In modern brewing many of the original top fermentation strains have been modified to be bottom fermenters. Currently the S. carlsbergensis designation is not used, the S. cerevisiae classification is used instead.

The yeast's function in baking is to ferment sugars present in the flour or added to the dough. This fermentation gives off carbon dioxide and ethanol. The carbon dioxide is trapped within tiny bubbles and results in the dough expanding, or rising. Sourdough bread, is not produced with baker's yeast, rather a combination of wild yeast (often Candida milleri) and an acid-generating bacteria (Lactobacillus sanfrancisco sp. nov). It has been reported that the ratio of wild yeast to bacteria in San Francisco sourdough cultures is about 1:100. The C. milleri strengthens the gluten and the L. sanfrancisco ferments the maltose.

The fermentation of wine is initiated by naturally occurring yeasts present in the vineyards. Many wineries still use nature strains, however many use modern methods of strain maintenance and isolation. The bubbles in sparkling wines is trapped carbon dioxide, the result of yeast fermenting sugars in the grape juice. One yeast cell can ferment approximately its own weight of glucose per hour. Under optimal conditions S. cerevisiae can produce up to 18 percent, by volume, ethanol with 15 to 16 percent being the norm. The sulfur dioxide present in commercially produced wine is actually added just after the grapes are crushed to kill the naturally present bacteria, molds, and yeasts.

The yeastlike fungus, Candida albicans, is commonly found in the mouth, vagina, and intestinal tract. Candida is a normal inhabitant of humans and normally causes no ill effects. However, among infants and individuals with other illness a variety of conditions can occur. Candidiasis of the mucous membranes of the mouth is known as thrush. Candidiasis of the vagina is called vaginitis. Candida also causes severe disease in persons with AIDS and chemotherapy patients.

Moulds

Moulds cause spoilage of food and fodder. Some strains produce mycotoxines such as ochratoxin in coffee and in cocoa which spreads out over the entire chocolate market.
They cause off flavor in food and destroy paper, wood, drugs, cosmetics etc. Moulds can cause allergies and infections.

Mouldy coffee in Trieste
In August 2006 great amount of Robusta coffee were found to be mouldy in Triest warehouse.
The beans in Trieste are thought to have been damaged by excess moisture on transport. Bags of coffee are dumped if they contain more than five mouldy beans or 10 partially mouldy beans per 500g.

Allergies
Allergies caused by moulds however are not so frequent as they seem to be. The most important sources of allergies are:

• Dogs,cats and other pets as 70% of all allergy cases.
  Get rid of dogs and cats and you have solved 70% of your problems.
• House dust, furniture, mites
• Pollen, grass
• Trees and shrubs
• Food with chemical preservatives, lactose, albumen, milk, eggs
• Odorous substances
• Moulds as last item of the list of allergenic sources.

To avoid mould allergy don't get in contact with cheese like Roquefort , Camembert or Brie cheese.
Keep perishable food always refrigerated to reduce mould growth.
Don't keep restover of fruits and vegetables in the kitchen. Keep it outside of the house.
Keep away from garbage [256].

Allergies

Allergies can be a serious threat to life and can end as anaphylatic shock. The allergens in foods represent a hazard for those who suffer from allergies, that is why the most important ones are cited here:

Allergens:

• Cereals containing gluten ( i.e. wheat, rye, barley, oats, spelt, kamut or their hybridised strains) and products thereof.) (Coeliac disease)
• Crustaceans and products thereof.
• Eggs and products thereof.
• Fish and products thereof.
• Peanuts and products thereof.
• Soybeans and products thereof.
• Milk and products thereof (including lactose).
• Nuts i. e. Almond (Amygdalus communis L.), Hazelnut (Corylus avellana), Walnut (Juglans regia), Cashew (Anacardium occidentale), Pecan nut (Carya illinoiesis (Wangenh.) K. Koch), Brazil nut (Bertholletia excelsa), Pistachio nut (Pistacia vera), Macadamia nut and Queensland nut (Macadamia ternifolia) and products thereof.
• Celery and products thereof.
• Mustard and products thereof: Mustard protein allergic individuals may react to the protein content of the mustard oil. Individuals sensitised to and by the skin sensitising component allyl isothiocyanate may react to oil in the absence of mustard proteins.
• Sesame seeds and products thereof.
• Sulphur dioxide and sulphites at concentrations of more than 10 mg/kg or 10 mg/litre expressed as SO2.

Preservatives: A small part of humans suffer fron allergy to preservatives. Labels like "Free of preservatives" must be true as some persons suffer heavy allergic responds to some preservatives. To avoid recourses due to cross over " No preservatives added" is being now labeled. This, however, does not solve the problem of allergic reactions.