A New Laboratory Mashing System

An assessment of the impact of oxygen and hydrogen peroxide on mashing and wort parameters has been made on a laboratory scale. Oxygen has been stridently eliminated by using an anaerobic chamber during mash analysis. Additionally the relative importance of proanthocyanidin species has been assessed by comparing the behaviour of "conventional" malt and a malt produced from a low proanthocyanidin variety. It seems that oxygen and peroxide act independently in causing the oxidation of thiolcontaining materials and polyphenols in mashes and that oxygen is not primarily exerting its impacts through the intermediacy of peroxide. The removal of thiols (presumably at least in part through the production of disulphide bridges between proteins) and of polyphenols (presumably via polymerisation) both contribute to increased wort turbidity and decreased rates of wort separation after mashing. Three inhibitors (nordihydroguaiaretic acid, ethylenediamenetetraacetate and potassium cyanide) have been employed in an attempt to differentiate between enzymic and non-enzymic events and also to identify whether lipoxygenase and peroxidase are catalysing key events. Whilst it seems that peroxidase has a key role in catalysing the oxidation of polyphenols by H 2 O 2 , it does not appear that either peroxidase or lipoxygenase is involved in the removal of measurable thiol. Nonetheless a significant proportion of the thiol elimination is likely enzyme-catalysed. We have been unable to demonstrate the production of hydroperoxides in mashes, but added hydroperoxide is undetectable, which suggests that these materials are either lost by onward conversion or by adsorption onto spent grains.

“…Mashes were prepared by the method of Buckee 17 with modifications. All mashes consisted of 50 g of milled malt combined with 150 g of deionised water.…”

Section: %8)6-%07 %2( 1)83(7mentioning

confidence: 99%

Laboratory-Scale Studies of the Impact of Oxygen on Mashing

Stephenson

Biawa

Miracle

et al. 2003

The Effects of Increased Steeping Temperatures on Enzyme Development in Malt

Baxter¹,

Reeves²,

Bamforth³

1980

Malts produced by steeping at 30°C for a total of 24 h including two air rests, frequently give the same results in routine analyses as do malts produced by steeping at 16°C for longer periods. However, the corresponding worts often filter more slowly under controlled laboratory conditions. The increased steeping temperatures can delay or reduce development of endopeptidase and p-glucan solubKase, but generally have little effect on the activity of o-amylase, carboxypeptidase, or endo-P-glucanase. The problems with wort separation are most probably due to high molecular weight p-glucan and disulphide-linked hordein persisting at the end of malting.

Effects of Raised Temperatures During Steeping and Germination on Proteolysis During Malting

Baxter¹,

O'Farrell²

1980

Raising the temperature from 16°C to 20°C or 25°C for prolonged periods during steeping or germination reduces HWE and TSN and slows down wort separation in laboratory mashes. When the higher temperatures are applied only during the last steep or the first two days of germination the initial rate of modification is accelerated, as is the development of a-amylase and endopeptidase. After four or five days germination the levels of enzyme activity are substantially lower than in the control malt. However, some barleys give malts with acceptable standard analyses after 4 rather than 5 days of germination.