As you sit enjoying your sparklingly clear pint of brewer’s brilliance you probably don’t think about the processes which have taken place in the cask to make it that way or why sometimes it’s far from brilliant. When the cask is delivered its contents look like something between cloudy beer and potage de jour. Either way you wouldn’t feel warm inside paying your hard-earned for it. The magic which transformed this turbid chaos into the beautiful order of crystal beer is electrostatic interaction.
Being aficionados of cask ale you will of course know of Isinglass and its origins in the belly of a tropical catfish. If like me you carry her picture in your wallet, you will also know that our beloved Saccharomyces cerevisiae resembles a tiny balloon. The active part of isinglass is a long stringy collagen protein covered with an electrostatic charge. The collagen molecule of isinglass is not quite dense enough to interest Lesley Ash so is easily dissolved in beer and floats around covered in (mostly) positive charges. The yeast balloons which are (mostly) covered in negative charges are drawn to the irresistible allure of the isinglass proteins’ positive charges. Like estranged lovers at the arrivals gate at Heathrow, the yeast and isinglass collide and embrace. These collisions and bonds occur millions of times to build up flocs (lumps) containing millions of yeast cells stuck to isinglass proteins. Watching the action of finings in a glass is quite impressive (if you’re easily impressed). Within minutes you can see the cloudy beer change to a clear beer with big lumps in it. After about an hour the big lumps are sediment and the beer above is as bright as a button. So why is my pint occasionally hazy you ask?
The interaction between finings and yeast relies on the correct conditions to work. The three most important conditions are:
1. Correct concentration of yeast
2. Correct concentration of isinglass
3. Correct pH
The first condition is hardest for the brewer to achieve. Bigger brewers use a centrifuge to remove the most of yeast before adding back the correct amount of yeast to condition the beer and fine effectively (in the case of one brewery, immobilised in calcium alginate gel beads). For smaller breweries the yeast in the cask is what is left over from fermentation in the brewery and the brewer must play a waiting game for the concentration to drop to the correct level before filling the cask. If you allow too much yeast into the cask there are too many suitors for the alluring Ms Isinglass and some of the yeast remains floating around as haze in the beer, probably feeling sorry for itself like a fat kid at the school disco. If there is not enough yeast, the sediment is too light to fully settle and chunks of it can be drawn out of the cask into your glass as haze or ‘floaters’. The same is true for too much isinglass.
pH is important because pH affects the charges on the isinglass and the yeast. pH is the concentration of positive H+ ions. If there are too many or too few of these, the allure of the isinglass or the randiness of the yeast will be reduced and your beer will be dull and murky.
The condition of the yeast is also important. Yeast cells change according to where they are and how they feel. When they are tired, emotional and facing starvation they tend to want to cuddle up to other yeast cells to increase their chances of survival. To do this they pepper the outside of their cells with charges in order to attract other yeast. If the brewer has left a load of sugar or other nutrients in the beer the yeast will be disinclined to leave the dining table and stick to other yeast or the isinglass. If the yeast is sick or dead it may also not have the capacity to be fined.
Another source of haze is of course an infection in the beer. If this is the case, you should be able to tell as the flavour of the beer would range from unusual to wrestler’s armpit.