HVG Germany: Hopfen


Polyphenols

Depending on the kind of hopping up to 30% of the polyphenols in the wort can come from the hops.

Nowadays polyphenols from barley malt or hops are more likely to be regarded as intrusive by the brewer. Because certain groups of polyphenols facilitate the formation of irreversible turbidity in the bottled beer. Therefore, in order to obtain a high physical stability they prefer to reduce the dosage of polyphenols or remove them. This is done e.g. by using especially bred proanthocyanidin-free barley varieties such as Caminant or by the use of polyphenol-free hop pure resin extracts. Alternatively polyphenols actively causing turbidity can be reduced by absorbing PVPP during the course of filtration.

However, this is in the face of an interesting development: Efforts have been increased in food and plant research to find natural antioxidants e.g. in herbs, tea or seeds. The effect of these antioxidants can be seen in two different directions: They can protect food - such as fats - from being affected in taste by oxygen or they act as radical catchers in the human body thus exerting an anti-carcinogenic effect. Examples of this are rosemary, tea - especially green tea - or red wine.

The dissolving behaviour of polyphenols in wort and beer is not identical for all components. Hydrophilic groups of substances such as hydroxybenzoles - or hydroxy-cinnamic acids, flavanols or proanthocyanidins - dissolve more easily than the more lipophilic prenyl-flavonoids; flavonoids are between these. The yield of the low molecular HPLC polyphenols with on an average 66 % is higher than that of the EBC polyphenols with 40 %, which is due to the better solubility of the hydrophilic, low molecular structure. Losses occur due to thermal changes and excretions with hot or cold break respectively, yeast and dregs as well as in the filtration.

Hitherto works on the polyphenol contribution hops make to the beer have shown the following:

• Froth and colour of the beers are not influenced negatively.
• With shorter boiling times no hard bitterness occurs - more likely the opposite occurs.
• Definite flavours can be achieved.
• The reducing power of the beers increases, the flavour stability increases. This also applies at least for the pilot extractions with relatively high oxygen content.
• Nevertheless the turbidity tendency increases particularly with longer boiling times (e.g. 80 minutes).
• The nitrate content increases according to the amounts dosed.

Therefore positive flavour effects can be achieved with hop polyphenols, especially when using aroma hops with short boiling times. An increase in the reducing power can be analytically accounted for and in the form of an improved flavour stability. The polyphenol dosage has a negative effect on the amounts of nitrate and - especially where there are longer boiling times - on the physical stability.