Extract brewers buy their sugar in a tin. All-grain brewers make it themselves from crushed malt and hot water, in a step called the mash. It looks a lot like making porridge, but underneath it is a small feat of biochemistry: enzymes that the maltster carefully kept alive wake up, chop starch into sugar, and hand you a sweet wort whose character you steer with nothing fancier than a thermometer.
Why Go All-Grain?
- Control — you decide how fermentable the wort is, which shapes body, sweetness and strength
- Range — any malt, any adjunct, any style you can dream up
- Cost — grain usually works out cheaper per batch than malt extract
- Satisfaction — it is the same process commercial breweries use, just smaller
The trade-off is a longer brew day and a few more variables to juggle. Brew-in-a-bag (BIAB), where you mash in a mesh bag inside your kettle, has made the leap far easier than it used to be.
Starch, Sugar and the Enzymes in Between
A barley kernel is essentially a packed lunch of starch for a baby plant. That starch is built from long chains of glucose — some straight, some heavily branched. Yeast cannot eat those chains directly; it wants small sugars such as glucose, maltose and maltotriose. Germination during malting creates the enzymes that do the chopping, and gentle kilning keeps them intact but dormant until you add hot water.
First, the starch granules must soak up water and swell open (brewers call this gelatinisation) so the enzymes can get at them. Malted barley manages this happily at normal mash temperatures; raw corn and rice need more heat, which is why some traditional lager brewers cook those grains separately before adding them to the main mash.
The Two Headliners
- Beta-amylase trims two-glucose maltose units off the ends of starch chains. It works best at roughly 60–65 °C but is fragile: according to Brew Your Own, much of it is destroyed within 40–60 minutes at 65 °C.
- Alpha-amylase slices chains at random points in the middle. That creates lots of new ends for beta-amylase to work on, but it also leaves behind branched fragments called dextrins that brewer’s yeast cannot ferment. It prefers about 68–72 °C and copes with heat far better.
Because neither enzyme handles the branch points well, some dextrins always survive into the finished beer. Those leftovers are a big part of what we perceive as body and mouthfeel.
The Supporting Cast
Older, less-modified malts leaned on cooler rests too:
- Beta-glucanase (about 35–45 °C) breaks down sticky gums that slow the runoff — useful with lots of rye, oats or unmalted wheat
- Phytase (a similar range) releases mild acids; the old “acid rest” lowered mash pH before brewers could simply adjust their water
- Proteases and peptidases (about 45–58 °C) trim proteins; with modern, fully modified malt a long protein rest can thin the body and weaken foam, so most brewers skip it
The Mash Temperature Cheat Sheet
| Rest | Temperature | Main Enzymes | Effect | Worth Doing Today? |
|---|---|---|---|---|
| Acid / gum rest | 35–45 °C (95–113 °F) | Phytase, beta-glucanase | Lowers pH, breaks down gums | Occasionally, for sticky grists |
| Protein rest | 45–58 °C (113–137 °F) | Protease, peptidase | Trims proteins | Rarely, mainly with undermodified malt |
| Low saccharification | 61–65 °C (142–149 °F) | Mostly beta-amylase | Very fermentable wort, dry beer | Pilsner, saison, crisp IPAs |
| Middle saccharification | 66–67 °C (150–153 °F) | Both amylases | Balanced | Most everyday ales |
| High saccharification | 68–72 °C (154–162 °F) | Mostly alpha-amylase | Fuller, sweeter body | Milds, sweet stouts, Scotch ales |
| Mash-out | 76–77 °C (168–170 °F) | Enzymes switched off | Locks in the sugar profile, thins the wort | Optional; handy for fly sparging |
Treat these as overlapping zones rather than hard walls. Enzymes work across a range, just more slowly away from their favourite temperature.
Single Infusion or Step Mash?
With modern malts, a single infusion — one rest of about an hour somewhere between 64 and 68 °C — handles almost every recipe. Both Brew Your Own and Craft Beer & Brewing point out that step mashing is now largely optional.
A step mash earns its keep when:
- The grist includes plenty of unmalted grain or heritage, undermodified malt
- You want finely tuned fermentability — for example, a long rest at 63 °C followed by a shorter one at 70 °C
- You are recreating a traditional process such as decoction for German lagers
Other Dials You Can Turn
- pH — aim for roughly 5.2–5.5 (measured on a cooled sample). Stray too far and enzymes slow down while flavours can turn harsh.
- Mash thickness — a thicker mash (less water per kilo of grain) shelters the enzymes; a thinner one tends to give a more fermentable wort.
- Time — conversion is often finished well inside an hour, but lingering at low temperatures pushes fermentability further.
- Calcium — healthy calcium levels help alpha-amylase stay stable.
Is It Done? The Iodine Test
Iodine turns blue-black when starch is present. Put a spoonful of mash liquid (no husks) on a white plate and add a drop of iodine solution. If it stays brownish-yellow, conversion is complete. Throw that sample away — never return it to the mash.
Safety and Legal Notes
- A full mash tun is heavy and scalding: lift with help, or use a pump or pulley
- Wear closed shoes and stir with a long paddle to keep hands clear of steam
- Once the wort is chilled, everything that touches it must be cleaned and sanitised
- Homebrewing rules differ between countries and even regions, so check yours — and remember that fermenting at home is one thing, but never distill spirits at home; it is illegal in many places and genuinely dangerous
Key Takeaways
- The mash turns starch into sugar using enzymes created during malting
- Cooler rests (around 62–65 °C) give drier beer; hotter ones (68–72 °C) give fuller body
- A single infusion covers nearly every modern recipe
- Keep an eye on pH, thickness and time, then let the iodine test give you the thumbs-up