The brewhouse yield indicates what percentage of the grist charge is available as extract content in the cast wort. The brewhouse yield is therefore an important internal brewery measure of the efficiency of the brewhouse operations.
In many countries, the taxation authorities are also interested in the brewhouse yield because it is only here that the total amount of extract formed can be determined. The main part of this extract later disappears because of conversion to alcohol and CO2 during fermentation, so only a small part is present in beer. It will be shown, however, that it is possible to determine the extract content of the so-called “original gravity” from the finished beer; the total extract produced can only be identified, however, by means of the brewhouse yield.
Calculating the brewhouse yield
In modern breweries, the brewhouse yield is automatically calculated on the basis of the determined values. The following section provides information on the thought processes and operating steps to determine the brewhouse yield which, in older and smaller breweries, also still have to be carried out. The brewhouse yield determines what percentage of the grist charge mass used is present as extract mass in the wort kettle. This percentage (brewhouse yield) is usually between 75 to 80%.
To calculate the brewhouse yield the following are required:
- the grist charge used,
- the mass percent determined with a hydrometerand
- the amount of cast wort measured.
The amount of grist used is registered exactly by the automatic weighing device and recorded in a computer or the brewhouse records. The amount of grist is the starting point for calculating the yield.
Factors affecting the brewhouse yield
The brewhouse yield depends on the following:
- the raw materials,
- the brewhouse equipment,
- the mash process,
- the lautering operations,
- the overall operating methods.
The yield is between 74 and 79%. It should be as high as possible and at most 1% less than the air-dry laboratory yield from the fine ground malt.
Raw materials
Malts give variable yields and an extract rich malt is highly prized. Poorly modified malts give smaller extracts than well modified malts. Since the grist is always recorded on an air-dry basis. the water content of the malt affects the yield. With an increasing water content, the yield decreases. Carbonate-rich water reduces the yield. Sulphate-rich water and very soft water, as a result of their pH-lowering nature, improve enzyme activity and thus the yield.
Brewhouse equipment
Modern brewhouses are designed to provide a high yield with good wort quality and use in order to do this a number of additional devices, in particular, to obtain the most complete extraction of the spent grains. They therefore produce higher yields than conventional brewhouses. The quality of a brewhouse is also judged from the difference between the actual yield obtained and the laboratory yield. In modern brewhouses, this difference is very small.
Mash process
A long, intensive mash process gives a higher yield. Longer boiling of the thick mash forms more extract. Premashing and boiling the mash under pressure increases the yield but at the expense of quality. The ratio of mashing liquor to sparge liquor is important since if too much mashing liquor is used the extract cannot be fully washed out and consequently the yield is less.
Lautering process
Uneven sparging and unequal flow through the lautering taps result in a lower yield.
More small sparges give a higher yield than continuous sparging. Lautering efficiency is reflected in the amount of soluble extract left in the spent grains. Use of the last runnings as mashing-in liquor for the next mash improves the yield slightly but not the quality.
Overall operating method
The entire brewhouse operation is based on supporting the enzyme activities. Optimal enzyme activity is, however, only possible when the pre-specified temperatures and times are adhered to exactly. This requires the person in charge of brewing to be accurate and reliable at all times and no superficiality or failure is acceptable. Otherwise, the damage done can be substantial.
To avoid this, in modern brewhouses, the programmes are stored in computer memories and operate completely automatically. The supervisor controls the process visually and has the opportunity to take over control at any time if it is necessary. In this way, operator errors are excluded and the process can be performed optimally.
