Lesson 6 - Wort Separation Process Control
This lesson deals with wort separation process control. The different methodologies of measuring and calculating extract recovery are explained and demonstrated. A methodology is explored, as is how to investigate and resolve performance issues with extract efficiency, wort quality, and cycle time.
Point of reflection – reconvene
Welcome back. So, what were your thoughts?
The difference to a large extent relates to the coarseness of the grind. A finer grind will make more of the starch granules available for conversion. In the previous lesson we learned that the plansifter coarse husk fractions (combined sieve one and sieve two) were mash tun – 36%, lauter tun – 26%, and mash filter – 5%. So, increasing the fineness of the grind increases the extract efficiency.
It is in the laboratory that we determine the available extract in the malt. The malt undergoes a specified milling regime. This grist is then used for a bench-scale mash, using specified conditions. The strength of the resultant wort allows calculation of the available extract.
The brewhouse hammer mill can produce a finer grind than the laboratory mill, and so mash filter extract efficiency can be greater than 100% of laboratory extract.
The two most common units of measurement we use to measure wort strength are Specific Gravity (SG) and ˚Plato (% w/w sucrose).
Specific Gravity is the ratio of the mass of a given volume of a solution at 20˚C compared to the mass of the same volume of water at 20˚C. We need to measure this at a standard temperature, as density changes with temperature. It has no units. However, as brewers, we will convert this SG to ‘gravity’. To do this we take SG, multiply it by 1,000, and then subtract 1,000. So if our SG is 1.062, we multiply it by 1,000, subtract 1,000, and declare our ‘gravity’ as 62 (this can also be referred to as 62 degrees saccharine). We will shortly see why this is useful for extract calculations.
˚Plato is a measure of the grams of extract in 100 g of solution (%w/w). For example, 9 g of sugar dissolved in 100 g of solution is 9 ˚Plato (Plato is actually based on the sugar sucrose, but our wort sugars give extremely similar results). In the brewing process, the liquid wort is practically measured as a volume rather than a weight. We thus need to determine the weight of extract in our volume of wort (% w/v). If we multiply the wort ˚Plato by its density, we have the very useful unit of kg extract/hL for our extract calculations later.
It is a common rule of thumb that gravity divided by four is equal to ˚Plato. This is only an approximation.
At gravity 40, the rule of thumb tells us that ˚Plato will be 10, and it is in fact quite close to this at 9.97.
At gravity 62, rule of thumb suggests that ˚Plato is 15.5, but it is in fact 15.2.
This rule of thumb is useful for quick mental comparison between the two units of measurement. It is not, however, accurate enough for calculating extract efficiency.