YEAST 



YELLOW 



B, a small formation pushes out from the cell 

 wall, and soon the new growth is shut off by a 

 wall of cellulose. It then becomes an inde- 

 pendent cell, from which others may grow. 

 Anyone can cause yeast to form by setting 

 aside a mixture of flour, water and sugar and 

 letting it ferment. The process takes about 

 three days, but may be hastened by the addi- 

 tion of a little vinegar. 



How the Yeast Works. The commercial 

 product may be used in any one of three 

 forms liquid, dry or compressed. However, 

 compressed yeast cakes wrapped in tin foil en- 

 joy the widest favor at the present time. In 

 the making of bread it is customary to mix the 

 yeast with a small portion of flour and water. 

 This mixture, with the addition of sugar and 

 sometimes potatoes, forms the so-called sponge. 

 The sponge is allowed to stand for a few hours 

 in some eases over night and is then mixed 

 with more liquid (water, milk, potato water or 

 whey) and flour to make the dough, which, 

 after thorough kneading, is covered and set to 

 "rise." Some housewives prefer a shorter proc- 

 ess, and they omit the .preparation of the 

 sponge. This is possible only when compressed 

 yeast is used. 



The yeast cells at once attack the starch in 

 the flour, which they convert into sugar, and 

 the latter substance is in turn changed into 

 alcohol and carbon dioxide. This change 

 makes the mass light and porous, the familiar 

 bubbles in bread dough being due to the bub- 

 bling up of the gas through the mixture. In 

 baking, the alcohol evaporates, and the yeast 

 germs are destroyed, so no taste of these sub- 

 stances remains in properly-made bread. Sour 

 bread results from the presence of acid fer- 

 mentations in the dough, a condition that 

 sometimes develops when bread is left to "rise" 

 an undue length of time. The principle, of 

 fermentation by the use of yeast is also em- 

 ployed in the manufacture of beer. 



How Yeast Is Manufactured. The yeast 

 plant is of such economic value that the manu- 

 facture of yeast for the baking and brewing in- 

 dustries has become itself an industry of im- 

 portance. Bakers' yeast and beer yeast are 

 not the same, the latter being too bitter for 

 use in bread making, though it is sometimes 

 thus utilized after undergoing a process of puri- 

 fying and sweetening. Dry yeast, or German 

 yeast, as it is sometimes called, is made by 

 introducing yeast previously obtained into a 

 liquor produced from barley, malt and rye, 

 called wort. When the wort is in a violent 



state of fermentation the yeast is skimmed off 

 and freed from the liquid by pressure. Com- 

 pressed yeast is made largely from the top 

 yeast of fermenting lager beer, which is forced 

 to the surface by the escaping carbonic acid gas 

 in the form of a yellow-brown foam. This is 

 skimmed from the fluid, washed and pressed 

 into cakes of a size to be marketed. B.M.W. 



Rrlntod Subjects. Interesting material con- 

 nected with this subject may be found in the 

 following articles in these volumes : 

 Bacteria and Bacteri- Cellulose 



ology Chlorophyll 



Beer Fermentation 



Bread Fungi 



Brewing Protoplasm 



Cell Spore 



YEATS, WILLIAM BUTLER (1865- ), an 

 Irish poet and dramatist who became the fore- 

 most figure in the so-called Irish Literary Re- 

 vival. It w r as not simply the fact that he went 

 for his material to the life and legends of Ire- 

 land that gave him this outstanding position; 

 it was rather the possession of a peculiar 

 "Celtic" temperament and genius, which fitted 

 him to express his native country so well. 



Yeats was born in Dublin on June 13, 1865, 

 and was the son of J. B. Yeats, an artist of dis- 

 tinction. For a time he studied his father's 

 profession, but before he was twenty-two had 

 turned definitely to literature. The exquisite, 

 elusive character of his poetry was recognized 

 immediately, and the publication of Cathleen 

 in Hoolihan, The Land of Heart's Desire, The 

 Pot of Broth, The Hour Glass and other plays 

 proved that his dramatic gifts were not in- 

 ferior to his lyrical genius. With Lady Gregory 

 he was instrumental in establishing the Irish 

 Literary Theater, out of which grew the Irish 

 National Theater Society, whose players be- 

 came known throughout America and Western 

 Europe. Yeats made lecture tours in the 

 United States and Canada in 1903 and 1914 and 

 was enthusiastically received. In 1916 he pub- 

 lished his Reveries over Childhood and Youth. 



YED'O, JAPAN. See TOKYO. 



YELLOW, yd' o, one of the three primary 

 colors of the spectrum. With blue it forms 

 green; with red, orange; blue, yellow and red 

 lights mingled give white light. As the appar- 

 ent color of the sun, yellow is held sacred by 

 some primitive tribes, and it is the national 

 color of China. Strong light increases the in- 

 tensity of yellow; most colors are dimmed by 

 it. Lemon and canary yellow are considered 

 pure yellow. See color chart, opposite page 

 1483. 



