First class ingredients must be used if we intend to make wines of high quality. Perhaps the most important ingredient of all is the yeast, since it is a living organism that carries out the fermentation and turns the sugar into alcohol.

We choose a strain of yeast that will give a clean fermentation with no formation of unwanted substances such as the evil-smelling hydrogen sulphide ("rotten eggs"). Our chosen yeasts should start the fermentation promptly, thus reducing the chance of the wine becoming contaminated with bacteria; it should settle firmly to the bottom of the fermentation vessel once the fermentation is over. The chosen yeast should preferably produce the maximum amount of alcohol from the sugar provided.

Not all yeast strains behave in the same way. Some work better than others at low temperature do, for instance, while others can tolerate quite high levels of alcohol. Accordingly we choose the yeast strain that is best suited to give us the style of wine we want.

The Gervin range of yeasts is selected from the active dried yeasts currently made for professional winemakers. All the strains selected have been exhaustively tested in the laboratory, and under conditions familiar to the amateur; members of the National Guild of Wine & Beer Judges have evaluated the wines made. The yeasts are sealed in triple foil sachets under nitrogen gas, which ensures a long shelf life if the yeasts are stored under cool, dry conditions.

No.1 Green Label (S.cerevisiae, Bordeaux strain 7013) This yeast is widely used in France to make both white and red wines. It starts quickly, works at temperatures down to 15°C and settles well at the end of the fermentation period. It will tolerate up to 100ppm of sulphur dioxide. It is recommended as general-purpose yeast.

No.2 Red Label (S.cerevisiae, Monrachet strain, Davis522) This is very vigorous yeast giving a rapid start to the fermentation. Excellent for all red table wines, it is especially recommended for making wines from autumn fruits such as blackberries, elderberries and sloes. It will ferment at temperatures down to 15°C. Because this yeast ferments vigorously, room should be allowed in the fermentation vessel to take possible foaming into account.

No.3 Yellow Label (S.cerevisiae (bayanus) Pasteur Institute strain) This yeast is designed to produce sparkling wines, so it tolerates higher levels of alcohol than most yeasts and is ideal for high alcohol dessert style wines. It is excellent for restarting a "stuck" fermentation due to too much sugar being added to the must. This yeast can be used for either white or red wines, and allows the wines to take on the main characteristics of the ingredients. It will ferment well in the 12-30°C range. The sulphur dioxide level should be kept below 25ppm.

No.5 White Label (S.cerevisiae, strain GVN) This French yeast is particularly good for making quality white fruit table wines. It forms little foam and ferments well at low temperatures (8-15°C), thus ensuring that the wines develop excellent bouquets. This yeast is used for the production of quality English table wines.

A Red/White Label (S.cerevisiae, Bordeaux SF strain) This French yeast was selected by INRA at Narbonne to compliment the characteristics of the grapes. It is used for the production of red Bordeaux (Claret) wines. It is described as an "aromatic" yeast, which develops a pleasant and lasting aroma. It produces minimal frothing, and produces a good yield of glycerol. It ferments well over the temperature range 18-35°C. It will tolerate up to 50 ppm of sulphur dioxide.

B Black/White Label (S.cerevisiae, Narbonne selection, CC strain) This is another high quality "aromatic" yeast, intended for the production of wines with a young fruity bouquet, similar to many of those from Germany. It starts easily, and produces little frothing. It ensures fermentation at temperatures down to 10°C, with associated formation of fruity esters.

C Gold Label (S.cerevisiae (bayanus) Strain EC1118) This yeast is said to be involved in the production of 70% of Champagne. It has similar characteristics to No.3 yeast, but is considered rather superior by many professional winemakers. It is recommended for making sparkling wines, dessert wines and for restarting "stuck" ferments. It is used worldwide for the production of high quality white and rosé table wines. It is valuable for producing high alcohol wines (up to 18.5%).

D Red on White Label (S.cerevisiae, strain 71B) This yeast has two particular characteristics. Firstly it produces an exceptionally fine bouquet. Secondly it can metabolise up to 35% of any malic acid present in the must. This makes the yeast very useful when the fruit basis (e.g. apples, gooseberries, rhubarb) may be overacid, with a high percentage of malic acid.

E Blue on White Label (S.cerevisiae, strain V1116) This yeast contains the "killer" factor, which helps to inhibit the growth of "wild" yeasts. It ferments well even when the nutrient level is on the low side, so it is ideal for the production of "honey" wines such as mead. It is further capable of producing wines of high alcoholic strength. Very "clean" wines are produced, allowing the flavour and aroma of the ingredients to dominate. It will ferment down to 10°C.