Soluble ash.
Colour.

Ready-formed carbo-hydrates.

At the same time he should make a physical examination of the malts as described on p. 37. The results of the analyses should be tabulated by the student and submitted to his instructor for criticism.

SECTION II

PRINCIPLES OF THE MASHING PROCESS.

PART I.

The Following Course of Experiments Constitutes a Study of Some of the Carbo-Hydrates Concerned in Wort Production, and Introduces the Student to the Special Methods Employed in their Examination.

Action of Water on Starch. The student during his previous course of work has examined starch granules from various sources under the microscope (p. 22). He should now study the action of water of gradually increasing temperature on starch.

Mix about 4 grms. of potato starch with 100 c.c. of cold water in a Jena glass beaker, and heat the mixture slowly, keeping it constantly stirred with a thermometer. Note that the starch granules commence to swell as the temperature of the water approaches 65° (149° F.), and as the temperature rises further they gelatinise completely and mix with the water, forming a semi-transparent viscid mixture called starch paste.

Boil the starch paste and note that it still remains viscid. Cool the paste, and its viscosity is much increased.

Boil 1 or 2 c.c. of the starch paste with 5 c.c. of Fehling's solution. No red precipitate of suboxide of copper is formed, showing that starch paste does not reduce cupric oxide.

Preparation of Soluble Starch.-Introduce about 50 grms. of potato starch into a 500 c.c. flask, and half fill the flask with a 7.5 per cent. solution of hydrochloric acid made by diluting 125 c.c. of the concentrated acid to 500 c.c. with distilled water. Allow the starch to digest with the dilute acid at the ordinary room temperature for seven or eight days. The acid should then be poured off and the starch washed repeatedly with distilled water by decantation until the granules no longer give an acid reaction when placed on blue litmus-paper. One or two drops of dilute ammonia should then be added, and the starch again washed until every trace of ammonia is removed. Drain the starch thoroughly on a filter, and spread it on filter-paper to air-dry at a temperature of about 25° (77° F.).

Examine the starch granules under the microscope, and note that in general appearance they are very similar to granules not treated by acid. Dissolve about 3 or 4 grms. in 100 c.c. of boiling water, and note that the solution differs from an ordinary starch paste in being limpid.

Study the Action of Dilute Sulphuric Acid on

Starch.-Prepare 200 c.c. of a 3 per cent. starch paste. When preparing starch paste note that the starch must not be introduced into boiling water as a dry powder, for under these conditions it forms lumps which do not gelatinise properly. The dry starch should first be mixed with a little cold water to form a thin cream, and the mixture should then be run slowly into boiling water with constant stirring until gelatinisation is complete.

2

When the starch paste is boiling gently, add grms. of strong sulphuric acid diluted with about 5 c.c. of water, and continue heating the mixture. The first noticeable change is the very rapid liquefaction of the starch paste owing to its conversion into “soluble starch ”.

At intervals of five minutes from the addition of the acid to the starch paste transfer two quantities of 5 c.c. each into two test-tubes. Cool one tube and add just enough of a dilute solution of iodine to develop its full colour. Add 10 c.c. of Fehling's solution to the other tube and heat it in a boiling water bath for ten minutes. Arrange the tubes in consecutive series, and note that, as the hydrolytic action of the sulphuric acid on the starch paste proceeds, the iodine-blue reaction of the original starch gives place to purple, reddishpurple, red, and finally to no colour; at the same time the precipitate of red oxide of copper in the series of tubes containing Fehling's solution increases rapidly in amount.

This experiment indicates that the hydrolytic action of sulphuric acid on starch paste is first to change it into a more soluble form (soluble starch), and afterwards to form a compound which gives a red reaction with iodine (erythro-dextrin), which is subsequently changed to a body which gives no colour with iodine. The increasing amount of red oxide of copper in the tubes containing Fehling's solution indicates the gradual production of a reducing substance (dextrose) as the starch is hydrolysed to its final point.

Prepare the Sugar, Dextrose, which is the Final Product of the Acid Hydrolysis of Starch.-Mix 100 grms. of potato starch with a little cold water to a thin cream and pour it slowly into 1,000 c.c. of boiling water in which 50 grms. of oxalic acid have been previously dissolved. When the starch is poured slowly into the boiling acid solution it is rapidly converted into soluble starch, and there is no difficulty in preparing a 10 per cent. solution in this manner.

Digest the solution for ten hours at 100° (212° F.) in a steam steriliser to completely hydrolyse the starch to dextrose. Neutralise the hot acid solution by adding an excess of calcium carbonate, and so remove the oxalic acid from the solution as insoluble oxalate of calcium. Filter, and concentrate the filtrate to a thick syrup on a water bath. Dissolve the syrup in twice its volume of 93 per cent. alcohol and allow the solution to cool