There are basically 3 factors that influences the quality and retention of berr foam:
Protein content
Amount of alpha acids
Carbonation (CO2)
If you produce worts or use malts that have higher protein content or use unmalted cereals with higher protein content than barley such as wheat, oats and rye (as you can see in the graph), the trend is that you have more quality in the foam of your beer.
On the other hand, proteins can also generate excessive turbidity, instability or even stuck sparge problems (filtration problems during brewing).
And we can classify these proteins according to their molecular weight as follows:
High molecular weight (insoluble proteins);
Medium molecular weight (important for beer foam and body quality);
Low molecular weight (essential amino acids for yeast nutrition during fermentation).
One factor that is important to be aware of is that some brewers do the protein stop.
This activity is nothing more than a rest during mashing, aiming at breaking high molecular weight proteins into medium and low molecular weight proteins, mainly occurring in the temperature range between 45°C and 55°C.
If you use a lot of unmalted cereals , you need to make the protein stop so that your wort has medium molecular weight proteins , because the high molecular weight ones will not help so much in the foam retention.
It turns out that some brewers make the protein stop even without unmalted cereal or higher wheat content in the malt grist , finding that the more temperature ramps they make, the better their beer will be.
But not really true...
When this happens, you will cause the medium molecular weight proteins that are present in barley and have already been broken down during the malting process, to be broken down into smaller molecules (low molecular weight proteins, which are basically amino acids).
As a result, you will have a wort with low medium molecular weight proteins and your beer will lose body and foam retention as well.
The alpha acids contained in hops will influence and favor the formation and retention of beer foam.
Hoppy beers will have more foam, so if you want more foam, you can go for hoppy beers.
It turns out that if you want to make a style that doesn't have a strong hop presence, like a Witbier, you can't just add more hops to promote the foam, the beer will be out of style.
Lastly, we have the carbonation of beer.
We can say that the more carbonation or the more CO 2 dissolved in your beer, the higher the formation of foam in your beer and, of course, when you have less carbonation, the lower the foaming beer.
If you have low retention, chances are you are not carbonating correctly.
To check if your beer is carbonated, it's nice to use a bottle gauge.
It is very useful for you who use priming in your beer brewing process, to calculate it correctly to get the carbonation you need in your beer.
But if you still feel that your beer is low on foam , there may have been a process failure (too long mashing could be one of the causes) or you may be producing a style that you naturally don't have.
For example, if you're brewing a Barley wine style beer and you follow its carbonation recommendation , you won't be foaming, as the style is still low carbonation.
On the other hand, if you decide to make a Weissbier- style beer , it will naturally have a lot of foam and carbonation, as you are going to use wheat (which has a lot of protein).
But a Weissbier is not a hoppy beer, how can it have foam?
You don't necessarily need all 3 factors (high protein, alpha acid and CO 2 content ) to have a good quality foam.
You can make the beer foam very good by making a correct mash and good carbonation.