Physical and Chemical Changes - Kilning Flashcards
What is the primary purpose of kilning in barley processing?
To kill the embryo while preserving enzymes
The preserved enzymes are crucial for the mashing process in brewing.
What is the effect of low temperatures during the initial stages of kilning?
They help preserve enzymes
This is important for maintaining enzyme activity for starch and protein breakdown.
What reactions occur when sugars and amino acids are exposed to heat?
They react to form Maillard or non-enzymatic browning products
These products contribute to the flavour and colour of malt.
What is the Maillard reaction?
A reaction between sugars and amino acids that creates flavour and colour in malt
It is responsible for the characteristic flavour and colour of malt.
How do ale malts differ from lager malts in terms of kilning?
Ale malts undergo more intense kilning regimes
This results in ale malts being more highly coloured and flavoured than lager malts.
What compound is formed from the precursor S-methylmethionine (SMM) during kilning?
Dimethyl sulphide (DMS)
DMS imparts undesirable vegetable-like flavours to beer.
What happens to S-methylmethionine (SMM) during the kilning process?
It splits into dimethyl sulphoxide (DMSO) and free DMS
DMS evaporates easily and is removed during kilning.
Why do malt analysis results often show SMM levels instead of DMS levels?
Not all SMM is converted by the end of the kilning operation
SMM levels are higher in malts with vigorous germination.
What is the relationship between kilning temperature and SMM levels in malt?
Higher kilning temperature and longer time reduce SMM levels
Ale malts, kilned at higher temperatures, have much lower SMM levels than lager malts.
What is nitrosodimethylamine (NDMA) and its significance?
A toxic, water-soluble compound that can cause cancer
Its formation is a risk in malting, especially with direct-fired kilns.
What factors increase the risk of NDMA formation during kilning?
Using direct-fired kilns and exposure to nitrogen oxides (NOx)
NDMA forms when hordenine reacts with NOx at high temperatures.
What is the industry standard for NDMA levels in malt?
Below 1 μg/kg
Some textbooks report a level of 2.5 μg/kg.
What is lipoxygenase (LOX) and its effect on beer?
An enzyme that can cause stale, cardboard-like flavours as beer ages
LOX can be removed by higher kilning temperatures.
How can malt specifications control lipoxygenase levels?
By requiring testing to ensure LOX is below a specific level
Some barley varieties do not produce LOX and are preferred.
