Mash Tun vs Lauter Tun

The definitions

Two jobs, often confused

These terms come from commercial brewing and get used loosely in homebrewing, which causes genuine confusion when someone tells you to “check your lauter tun” and you own one vessel.

• Mashing is the conversion step. Grain and hot water rest together at a controlled temperature -- typically 148 to 158°F for an hour -- while the malt’s own enzymes break starch into fermentable sugar. The vessel that does this is a mash tun, and its defining requirement is holding a temperature.
• Lautering is the separation step. The sweet wort has to be drained away from the spent grain, using the grain husks themselves as a filter bed. The vessel that does this is a lauter tun, and its defining requirement is a false bottom or manifold that holds back solids while passing liquid.

In a commercial brewery these are frequently separate vessels, because separating them lets you start mashing the next batch while the first is still lautering. That is a throughput concern, and throughput is not a homebrew problem.

Why homebrewers combine them

One vessel does both

An insulated cooler with a false bottom is a mash tun and a lauter tun simultaneously. You mash in it for an hour, then open the valve and drain the wort off through the false bottom. One vessel, both functions, and no downside at a 5 or 10 gallon scale.

Single-vessel electric systems take it further and do all three jobs -- mash, lauter and boil -- in one vessel, using a lift-out grain basket with a perforated base as the lautering element. That is why the all-in-one category exists and why it suits homebrewing so well: best electric brewing systems.

The only time separating them makes sense for a homebrewer is if you are brewing back-to-back batches on the same day and want to start the second mash while the first drains. That is rare, and it is the commercial reason transplanted.

Sparging

The terminology that goes with it

Lautering usually involves sparging -- rinsing the grain bed with additional hot water to recover sugar that would otherwise stay behind. Two approaches, and they place different demands on the vessel:

• Batch sparging. Drain the mash completely, add a batch of sparge water, stir, rest briefly, drain again. Simple, forgiving, and it does not depend on an intact husk filter bed because you are stirring anyway. This is what most cooler mash tuns do.
• Fly sparging. Trickle sparge water onto the top of the bed at the same rate you drain from the bottom, so the bed stays submerged and the rinse is continuous. More efficient and far more dependent on an undisturbed, permeable grain bed -- which is why fly spargers crush at wider gaps to keep the husk intact. See grain mill gap settings.

The hardware that matters

The false bottom, not the vessel name

Whichever terminology you use, the component doing the lautering work is the false bottom or manifold, and its design determines whether your runnings flow:

• Domed perforated plate. Best option. The dome resists collapse under grain weight and traps less wort beneath it than a flat plate.
• Stainless braid. Cheap and effective in a cooler. Prone to crushing under a heavy bed and harder to clean.
• Slotted copper manifold. Traditional, effective, and a weekend project. Distributes draw across the bed better than a single pickup.

Detail in false bottoms explained.