C_{6}H_{10}O_{5} + H_{2}O   —­>  C_{6}H_{12}O_{6}
starch      water          dextrose

This reaction is carried out on forty million bushels of corn a year in the United States.  The “starch milk,” that is, the starch grains washed out from the disintegrated corn kernel by water, is digested in large pressure tanks under fifty pounds of steam with a few tenths of one per cent. of hydrochloric acid until the required degree of conversion is reached.  Then the remaining acid is neutralized by caustic soda, and thereby converted into common salt, which in this small amount does not interfere but rather enhances the taste.  The product is the commercial glucose or corn syrup, which may if desired be evaporated to a white powder.  It is a mixture of three derivatives of starch in about this proportion: 

Maltose          45 per cent. 
Dextrose         20 per cent. 
Dextrin          35 per cent.

There are also present three- or four-tenths of one per cent. salt and as much of the corn protein and a variable amount of water.  It will be noticed that the glucose (dextrose), which gives name to the whole, is the least of the three ingredients.

Maltose, or malt sugar, has the same composition as cane sugar (C_{12}H_{22}O_{11}), but is not nearly so sweet.  Dextrin, or starch paste, is not sweet at all.  Dextrose or glucose is otherwise known; as grape sugar, for it is commonly found in grapes and other ripe fruits.  It forms half of honey and it is one of the two products into which cane sugar splits up when we take it into the mouth.  It is not so sweet as cane sugar and cannot be so readily crystallized, which, however, is not altogether a disadvantage.

The process of changing starch into dextrose that takes place in the great steam kettles of the glucose factory is essentially the same as that which takes place in the ripening of fruit and in the digestion of starch.  A large part of our nutriment, therefore, consists of glucose either eaten as such in ripe fruits or produced in the mouth or stomach by the decomposition of the starch of unripe fruit, vegetables and cereals.  Glucose may be regarded as a predigested food.  In spite of this well-known fact we still sometimes read “poor food” articles in which glucose is denounced as a dangerous adulterant and even classed as a poison.

The other ingredients of commercial glucose, the maltose and dextrin, have of course the same food value as the dextrose, since they are made over into dextrose in the process of digestion.  Whether the glucose syrup is fit to eat depends, like anything else, on how it is made.  If, as was formerly sometimes the case, sulfuric acid was used to effect the conversion of the starch or sulfurous acid to bleach the glucose and these acids were not altogether eliminated, the product might be unwholesome or worse.  Some years ago in England there was a mysterious epidemic of arsenical poisoning among beer drinkers.  On tracing it back it was found that the beer had been made from glucose which had been made from sulfuric acid which had been made from sulfur which had been made from a batch of iron pyrites which contained a little arsenic.  The replacement of sulfuric acid by hydrochloric has done away with that danger and the glucose now produced is pure.