There are three constituents, namely, heat, light, and moisture, which in varying proportions make up what is known as climate.  The first two, heat and light, are derived from the same source—­the sun—­and may, therefore, be conveniently considered together.  The more heat and light a vine receives the more vigorously it grows.  What is more important, however, is that the wine from it becomes stronger.  It gains in strength because the percentage of glucose increases in the must:  the must being the juice pressed from the grape, but in which fermentation has not commenced.  Accordingly we find that the wines of the warmer regions in new South Wales, Victoria, and South Australia are much stronger than those from the cooler parts.

It is important to remember that the unripe berries of the grape contain several acids, notably tartaric, citric, and malic acids.  As the fruit begins to ripen, these acids act upon the various substances, namely, starch, gum, dextrine, lignine, cellulose, &c., also contained within it, and grape sugar or glucose is formed in consequence with the advent of ripening, therefore, the fruit becomes richer in sugar and poorer in acids; part of the acids, in addition, is neutralised by the mineral salts which are absorbed by the roots.  These acids, however, are not so thoroughly neutralised in a cooler climate, and as a result the wine has often a sour, crude taste.  The warmer the climate the more alcohol the wine will contain; indeed, it may become too strong.  On the contrary, the cooler the climate the more of acid there will be, and it may possess in consequence a crude, sharp taste.  But these are matters which can be rectified by choosing the right varieties of grape for the different localities, and by their proper cultivation.

The third element concerned in the climate, namely, moisture, has now to be considered, and it is important from the fact that in a moister climate the percentages both of glucose and of acids in the grape are diminished.  It is also important for another reason, namely, that while heat and light are unalterable, moisture may be produced by irrigation.  This constitutes one of the vexed questions connected with viticulture, and the most diverse opinions have been expressed about it.  Some believe that irrigation is of great value, while others cannot say enough against it.  But it would seem that when judiciously employed it is of unquestionable advantage.  It renders the cultivation of the grape possible in places where it would otherwise be impossible; it largely increases the yield; and, what certainly must not be forgotten, it enables a lighter wine to be produced in the warmer regions.  And another argument in favour of irrigation is this, that there is far more fertilizing matter in river water than in rain water.  Hence it is that irrigation greatly enriches the land and increases the yield.  It is thus a powerful aid, and because its advantages have been abused, that is no reason why it should not be made use of in a rational and scientific manner.