In this lesson, I want to address gushing. I'll start with a story. A number of years ago I was the examiner for one of the institute of brewing exams, these days Institute of Brewing and Distilling and I set the question, write an essay on gushing. I'll never forget the guy, I assume it was a guy from some of the words he used and certainly in America. The essay went something like you had one hell of a day in the office. Your boss is a jerk. The water machine isn't functioning and the air conditioning is out of order. It's a sweltering whatever Fahrenheit he said, in the office. When you go to leave that evening, the elevator is out of commission and you have to go down 25 flights of stairs. You hit the sidewalk, that's how I knew it was an American guy, supposed to pavement and it's a sweltering whatever Fahrenheit outside. I would say something like 35 degrees Celsius, anyway. You tread in some dog debris and you get home to your apartment and that elevator is out of commission as well, so you've got six flights of stairs. You throw open the door, you find your air conditioning is not working either. You find the cat has been sick on the carpet. You throw on the TV and you find the Yankees are down six zip. You go to the refrigerator and you take out a beer and you open it and it goes whoosh. Well, that's gushing. That was it. That was the essay. He got two marks. A, he knew what gushing was. B, he entertained me, but a gushing in a beer is certainly not entertaining. The last thing in the world you want is this phenomenon. Basically, it's all about nucleation sites. If you cast your mind back to what we have discussed when it comes to bubble formation, beer does not spontaneously foam unless you've got something on which the bubbles can come out of solution. There are various causes of gushing. One could be excessive carbonation. Another one could be oxalate. Oxalic acid, if that gets into beer and it can form little particles, bits in the beer and on those particles you will get carbon dioxide being produced. I remember once I was with Graham Stewart in India and we were drinking beer and it was gushing. When we looked at the beer, we found there were slivers of glass in the tiny little slivers of glass. Those glass bottles are obviously not been properly washed before they've been filled with beer and that glass from the nucleation site. Actually, when we realized it was glass, we were more worried about the gushing. Rough inside surfaces of bottles. When you make hop preparations, some of them can have oxidized and dimerized components. There are materials in these hop extracts that can cause gushing. Certain metal ions can cause gushing. You may not get much of them in beer like Nickel, but nonetheless, there is a history of looking at that. If you get filter aid particles, diatomaceous earth or perlite getting into the beer for whatever reason, they can cause gushing. Agitation. If you drop a beer bottle you're going to get gushing. You might have a friend who thinks he's ever so smart to shake your beer bottle, lose the friend. Agitation is a problem, but most of the research that goes on in beer gushing and much of it is in Europe, is on a molecule called hydrophobin. I've said a lot about hydrophobicity. I've said that hydrophobic regions are important for foam stability. Hydrophobin is a very intensely hydrophobic small protein. What happens if it gets into beer these little hydrophobin molecules stick together and they make something which these days is referred to as nano bombs. These stuck-together hydrophobin particles are very powerful nucleation sites for bubble release. Where does this hydrophobin come from? It comes from certain molds that can contaminate grain. The most extensively studied is something called fusarium. If you have fusarium contaminating the barley or other grains, then it will produce hydrophobin. That will lead in the finished beer to gushing. Now, fusarium produces two things we worry about. The first is hydrophobin. The second is a substance called deoxynivalenol, which you'll be pleased to know we can abbreviate to DON. It's also referred to as vomitoxin. That tells you everything you need to know about DON. It's of serious health risk. Now, it's very hard to measure hydrophobin, but it's very easy to measure DON. One of the things that some brewers have on the specification for the malt and the malt will have on the specification for the barley is DON. To make sure it is of a very low level and barely detectable. If you got DON there, you've got hydrophobin because you got fusarium. This is a much bigger problem in countries like Northern Europe, which are colder and wetter and the risk of fusarium is much higher than it is in the classic regions for growing barley, for example, in the United States and Canada. It's usually not a major problem in North America, but it can be a big problem in Northern Europe. That's why you'll see much of the research that's published, there is a lot of research being published recently, comes out of locations in Europe. Fusarium producers deoxynivalenol, which is the marker substance for contamination.
