Germans take their beer's appearance seriously. In particular, the foamy head's size and shape tells them a lot about the beer already even before they sniff the aroma. A creamy head with rocky cascades tells you that this brewer knows how to make beer. It's probably going to taste wonderful.
And a good head adds much to the taste as well, by slowly releasing esters and flavonoids that give you a powerful aroma. As you probably know, aroma is the most important part of taste.
So what is it that makes this beautiful head? The answer breaks down to at least 6 different components that the brewer has to get just right for the perfect head, which of course is only a part of what makes a perfect beer.
Carbonation
Proteins
Hops
ABV
Glassware
Cleanliness
The first thing is the most obvious: high carbonation levels. The gas bubbles rising up from the beer are the basis of a good head. Artificial carbonation can be added to the bright tank, but it's much better if the natural CO2 is preserved from the fermentation. Natural CO2 gas makes finer bubbles that give a creamy texture to the head. Göller Brewery, for example, achieves highly carbonated beer naturally by a process of kräusening, which is adding some fresh wort to already fermented beer in order to reinvigorate the CO2 levels.
But CO2 is not the only part of a good head. As you know, highly carbonated soft drinks lose their head almost immediately. The thing that makes a beer head stick around is a fine coating of proteins around the CO2 bubbles, locking them in the low pressure zone above the liquid, which we call foam.
These protective proteins are medium-length strands that occur in malts. The higher the protein content of your malt, the better head retention you can expect. Wheat malts, for example, are very high in protein, so they will make a beautiful, thick head as you see in a Bavarian Hefeweizen like the Steinhauer Weisse from Göller.
These malt proteins, called Lipid Transfer Protein 1 (LTP1) are hydrophobic (don't like water) and so they tend to cling to the gas bubbles, surrounding them and preserving them for a long time.
A good brewer will be careful to retain LTP1 by his mashing technique. For example, allowing protein rests for too long at lower temperatures will break up these medium-length proteins. Generally, a higher mash temperature of about 158F (70C) ensures more protein body, and thus a fuller body and head retention.
This also means certain malts work better than others. A high quality, 2-row barley will leave more protein than a 6-row variety. Göller uses local 2-row barley that has grown in the area for centuries, providing a classic level of modified malts. Modern varieties of barley are highly modified. Modification denotes the chemical breakdown of compounds that reside naturally in grain. For brewers, the key substances in grain are starches and proteins. A highly modified malt means that most of the starches and proteins are broken down for fermentation. This is great for fermentation, but not great for a full bodied beer, or a rich, creamy head.
You will also notice that many American beers that include adjuncts like corn will have very poor head retention. This is because of the low protein content in these adjuncts, as well as some extra fats and oils that inhibit head retention. A Reinheitsgebot standard brewer like Göller, on the other hand, will add no adjuncts to their beer, so you can always expect a tall and healthy head on a Göller beer.
The next factor that plays an important role in head retention is hops, which tend to stabilize the LPT1. The iso-humulones (alpha acids from hops) give the bubbles a longer lifetime by supporting a higher surface tension. A well hopped pilsner like Göller's Original will keep its head for 10 minutes or more.
The ABV plays a role too. Higher alcohol levels will reduce head retention, which is why you will notice that barley wines and bocks have less head. They will feel heavier on your tongue. On the other hand, too low ABV won't work either. The moderate 4.9% ABV of the Original Pilsner keeps the balance for a proper head. The pils feels light and refreshing, due in part to the higher effervescence and foam retention.
Finally, glassware plays a role. The tall, vase-shaped glasses used for Hefeweizen leave a smaller surface area for evaporation of CO2 gas. These glass styles help the head to last longer, and can increase the aroma as well. Usually a good beer glass has etching on the bottom to promote the formation of bubbles.
And don't forget to keep a clean glass, free of soap residue or fatty substances. In general, cool, clean glasses and containers will help retain the beer's aroma and head longer.
As you see, it isn't one thing or another that makes a difference in a healthy head on your beer; it's all of them!