mashout
The step or process, in brewing beer, of raising the mash (e.g. by adding hot water to it) to a temperature around 75 °C or 170 °F, so as to stop the enzymatic conversion of starch to fermentable sugar and make the mash and wort more fluid.
mashout: the temperature hold that stops enzyme action
In beer brewing, the mashout is a deliberate heating step performed near the end of the mash cycle. The brewer raises the temperature of the grain and liquid mixture, called the mash, to approximately 75°C (170°F) and holds it there for a defined time, typically 10 to 15 minutes. This temperature denatures the amylase enzymes that have been converting starches into fermentable sugars during the earlier mash rest. Mashout stops enzymatic activity and prepares the mash for lautering, the process of separating liquid wort from spent grain solids.
The mashout serves two practical functions. First, it halts starch conversion at a chosen point, allowing the brewer to control the final ratio of fermentable to non-fermentable sugars in the wort, and thus the beer's final gravity and body. Second, the higher temperature reduces the mash viscosity, making it flow more readily during lautering and improving the efficiency of liquid extraction. Without mashout, the thick mash becomes difficult to sparge (rinse with hot water), and wort flows slowly through the grain bed.
The mashout temperature is critical. Below 70°C, enzymes continue to work and the purpose is defeated. Above 77°C, the grain proteins and starches begin to absorb water and swell, thickening the mash again and making lautering harder. Most brewers target the narrow band between 75 and 76°C. Some breweries omit the mashout step entirely, using cooler lautering methods or accepting slower sparges. All-grain homebrewers and commercial operations typically include it as standard.
The mashout is performed in the same vessel where the mash has been resting, usually a mash tun or lauter tun. Hot water is added slowly to raise the temperature gradually, or the vessel itself is heated with direct steam or heat exchanger systems if the equipment allows. The grain bed must be stirred or recirculated carefully to ensure even heating without compacting or tearing apart the grain particles, which would increase turbidity and tannin extraction in the wort.
Modern brewhouses with automated controls often program the mashout as a discrete step with temperature and time parameters. In manual systems, a brewer monitors the mash temperature with a probe thermometer and adds hot water or opens heating valves as needed. The mashout marks the transition from the mash-in and rest phases to the runoff (lautering) phase. It is distinct from the later sparging step, in which additional hot water is sprayed over the grain bed to rinse out residual sugars.