I was baking a loaf of bread, and for some reason, it didn't turn out as voluminous as it should have, so I decided to investigate what the problem was. The 2 loaves I had baked earlier too were not quite up to the mark so my suspicion fell on the yeast that I was using. I use fresh baker's/cake yeast, and it goes bad really fast. It has a refrigerated shelf life of about 3 weeks, but I had stored it in the deep freezer so that it was stored frozen. Baker's yeast can be stored frozen up to 6 months. The yeast I had was about 5 weeks old and had changed in both colour as well as texture.
Baker's or Fresh Yeast that you get in India is basically cake yeast which is available in cuboids starting from 500g. It costs Rs. 30 for 500g, and Rs. 56 for 1 kg. The brand I buy is called "Tower". Now this yeast when fresh has a creamish-yellow colour, and has a crumbly texture. i.e. It should crumble easily when you try to crumble it. If the colour changes to a somewhat darker shade and the texture becomes more paste-like(and hence does not crumble), it means your yeast has been working and is probably "tired". I do NOT know how to check yeast for tiredness because this "tired" yeast when mixed with sugar and water WILL bubble, but when you make bread, won't give a good second rise. And that is exactly what happened with me. I had stored a small amount of yeast in the refrigerator in what I thought was an air-tight container, but it was letting water vapour in so that was what had tired out the yeast. So when you start making bread, make sure your fresh yeast is creamish-yellow in colour and crumbly in texture. Also if it is tried out, it will smell very beerish(will smell of alcohol). Fresh yeast should have a yeasty smell and not a beery smell.
Storage: As far as storage is concerned, this is what I do. I buy about 250g of yeast(enough to make about 20-25 loaves of 400g bread; 300g flour and rest water) and store it in the deep freezer in an air-tight plastic wrap. Every few weeks, I remove about 1/5th the yeast and transfer it into an air-tight plastic box to store in the refrigerator. This is because frozen yeast does not crumble. Also before breaking off the yeast, I leave it in the refrigerator to thaw for at least 6 hours after removing it from the deep freezer.