The ultimate quality of concrete is usually assessed by compressive strength. Concrete classes, specifications, requirements and compliances are all based on 28-day compressive strength. The quality assurance systems assume that if quality and quantities of the concrete constituents do not change from batch to batch, the 28-day strength should be consistent within acceptable variation expressed in standard deviation. This is true, when all the above is known, and reliably measured. However, if this is not known, but only assumed to be known, then changes in concrete quality might be gone undetected until some strength results become available. But this may take 7 or even 28 days until it is realised that quality of concrete was jeopardised. The concrete yield test can be of a great assistance to appreciate some of the issues with produced concrete mixes while other commonly used fresh concrete tests and indicators may fail to identify the problems.