However, even the complete removal of oxygen would not be able to prevent enzymic degradation by the lipoxygenases. The lipoxygenases (LOX) are formed during germination and preferably stored in the acrospire and rootlet s. In malt the enzyme is therefore particularly enriched in the acrospire. The enzyme has an optimum pH value of 6.0 and is very susceptible to high temperatures. A considerable proportion of the lipoxygenases (LOX) is therefore destroyed during kilning, more in the case of dark malt than of pale. Nevertheless, more than a third of the lipoxygenases remain activated in the malt. Through milling, the lipoxygenases (LOX) present in the acrospire are quickly activated and at the still frequent low mashing temperatures and high pH value of the mashing water are able to split the unsaturated fatty acids in a relatively short time and thereby produce autooxidation products, which can later lead to ageing carbonyls.
Even very small amounts of hydroxy fatty acids which find their way in the form of intermediate products into beer represent a danger for the flavour stability of the beer. Unsaturated fatty acids are very quickly degraded to intermediate products which come into question as a precursor for the stale flavour. In Fig. 3.44, the process of lipid degradation during mashing is shown in abridged form [352, 353); the intermediate products are generally summarised under the denotation hydroxy acids or hydroxy fatty acids. Oxidation of the unsaturated fatty acids begins with the destruction of the reduced system of the malted corn, i.e. with comminution.
Since, however, unsaturated fatty acids are always present in malt, their oxidation can only be prevented by the strict avoidance of oxygen.
Essentially it leads to shorter shelf life and flavor instability.
Weizen - not everyone can afford copies of these books, linking a page to the book is a little rude in my opinion. I was lucky enough to find some images on Google and facebook to grab some of these quotes. Its all in the hope that we can educate eachother and become better brewers for it.Statistics: Posted by caedus — Sun Jan 08, 2017 1:43 pm
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