This section relates to the mashing and sparging process: extracting sugars from grain and collecting it as wort in the kettle. The mash is performed in a mash tun and the sparge is performed in an lauter tun. Those vessels can be combined into a single mash/lauter tun.
The starches in the grains are broken into fermentable sugars by amylase enzymes during the mash. The simpler carbohydrate chains are broken down by beta amylase enzymes, and the more complex carbohydrate trees are broken down by alpha amylase enzymes.
The temperature of the mash is one of the most critical elements of brewing. A higher temperature leads to a less fermentable wort, resulting in a sweet final beer. A lower temperature leads to a more fermentable wort, resulting in a dryer beer. Too high or too low of a temperature can cause off flavors or poor efficiency. The most common range for a single infusion mash is 148F - 158F (64C - 70C).
Amylase enzymes cannot act on the starches until they gelatinize, which happens in barley at 140F (60C). Starch conversion ends if the mash temperature falls below 140F.
Beta amylase enzymes are most active in the 140G - 150F (60C - 65.5C) temperature range. Above 160F (71C), beta amylase enzymes deactivate.
Alpha amylase enzymes are most active in the 162F - 167F (72C - 75C) range. Above 176F (80C), alpha amylase enzymes deactivate.
Reference: The Theory of Mashing
The ratio of water to grain is important when mashing. Typical range is 1.0 - 2.5 quarts of water per pound of grain (2.0 - 5.2 L/kg). A thicker mash (<1.25) tends to finish quicker, with less fermentable sugars. A thin mash (>2) can take longer to finish, but results in more fermentable sugars. Most brewers aim for the middle ground, a 1.25 (2.6L/kg) to 1.50 (3.2L/kg) ratio. Modern malts, however, show little difference in fermentability based on mash thickness, but speed of completion is still an issue. 1)
The amount of liquid absorbed by the grain varies based on grains used and sparging method used (mostly whether you can squeeze the grains, as in brew-in-a-bag systems). The typical estimate is 1 pint per pound (1 liter per kg) in non-squeezed mashes.
Various calculators report an estimated 1 gallon of displacement per 12 lbs of grain, or 1 liter per 1.5 kg. This is after absorption; the instantaneous displacement is higher until the grain has taken in some liquid.
For mashing in a 30L mash tun, 10kg of grain would displace 6.66L, meaning 23.333 L fits in the tun with the grain for a grist ratio of 2.3 L/kg. This is slightly thicker than average, but well within the acceptable range.
When the mash is finished, it is common to raise the temperature a bit to stop the enzymatic activity and increase the viscosity of the liquid so it drains from the grain bed more efficiently. The mash out temperature is typically 170F (70C).
A sour mash is when the wort temperature is allowed to fall into the 90F - 120F temperature range, where bacteria and wild yeast are active. This can either be during the mash or after collecting the wort. The infection causes the mash or wort to taste and smell sour. The wort can then be boiled, killing the infection to prevent further souring. This method is used to create sour style beers in a controlled and comparatively quick manner, thought the sourness is different from that of a sour fermented beer.
A common technique is extracting 20% of the wort after the mash, souring it, and adding it back to the normal wort after a few days to revitalize fermentation and mellow the sourness.
Eff = 100 * (gravity points of wort * wort volume) / (grain weight * grain extract potential) 2)
Vorlauf is the process of taking some of the mash water out from below the grain bed and pouring it back on top. Some of the flour and grain husks always fall into the wort, and pulling those small particles and putting them back on top helps to reduce the debris in the wort.
Recirculation is the process of moving wort from below the grain to above it continuously during the mash, either manually or with an electric pump. Recirculation has the same wort clarification benefit as the vorlauf, and supposedly “sets the mash bed” so it becomes a sort of dense particle filter. It has the added benefit of equalizing the temperature across the entire mash, including within the grain bed. This gives a better measurement of the actual mash temperature, and, in the case of a temperature-controlled mash, it ensures that all parts of the mash are at the measured temperature.
Some systems control the temperature of the mash by running the recirculated liquid through a heated tank, while the mash tun itself is not directly heated. Others heat the bottom of the mash tun directly, beneath the liquid, and the circulation equalizes the heat throughout the tun.
Sparging is the process of rinsing the grain bed after the mash with clean water to extract any remaining sugar that did not drip out via gravity. The purpose is to increase efficiency: get closer to the theoretical maximum sugar extraction.
Sparge water is typically heated to “mash-out” temperature (170F / 70C) to ensure good viscosity while avoiding tannin extraction. There is much debate about it, however, and some have argued that cold water works just as well.
Two popular methods of sparing are “fly sparging” and “batch sparging”.
Batch sparging is the simplest way of rinsing the grains. It involves simply dropping them all into another container full of water, possibly recirculating if desired, and then collecting the filtered sparge water.
In brew-in-a-bag setups, the whole bag is lowered into a container of sparge water and steeped like a tea bag, then removed and drained.
Fly sparging is the process of actively pouring sparge water over the top of the grain bed and collecting the runoff as it exits from the bottom. The water is poured very slowly to avoid forming channels through the grain bed, since big channels prevent the water from reaching the rest of the grains.
A “stuck sparge” occurs when water stops filtering through the grain bed and cannot be collected from the bottom. This can happen for mechanical reasons – the grains clogging the exit pipes – or from the grain bed itself becoming too firm for liquid to freely flow through. Certain grains become gelatinous during the mash, and grain bills heavy in such grains can form a thick grain bed that liquid does not flow through. Rice husks can be added to the mash to keep the grain bed porous without affecting the flavor.