Underlet mashing

I'm so excited to have found some stuff on underlet mashing. Another one of my multiple obsessions.

A widespread method was underlet mashing. A technique that was developed in the last half of the 19th century and remained popular way past WW II. It wasn’t as common in Scotland as in England, but it was still practised north of the border, for example at Maclay. 

After an initial mash at quite a low temperature, 30 minutes later, more hot water was added via the underlet, i.e. from the bottom of the mash tun. The internal rakes were given a couple of spins to mix the new water through the mash. The underlet water was at a hotter temperature than the striking heat and raise the temperature of the goods. In effect it’s a step mash.

After standing for 120 minutes or so, the wort was run off and there were one or two sparges. The exact details varied from brewery to brewery. Because of the need to stir the mash after the underlet, brewers had to have rakes fitted to their tuns. 

There was an explanation for using the method other than improving extract.

“Underletting was not brought into favour merely as assisting in obtaining full extract, but by mashing at a lower initial temperature and then bringing the goods heat up to a high temperature by underlet, it was thought to obtain a wort of more desirable carbohydrate composition for certain classes of beer. There is some reason to think that a sweeter beer was thus obtained. But apart from carbohydrate composition due to controlled diastatic action, there is the question of proteolytic action being more effective at the lower initial temperature and so affecting the nitrogenous composition of the wort favourably. Many experiments have shown that 148°-150° is the temperature at which proteolytic action in the mash tun is inhibited, but at 144 -145º it is positive so that 20 minutes to half an hour at this lower figure might have a very desirable effect in reducing the amount of those bodies which are potentially troublesome in bottled beers. Moreover when an underlet is to be used the mash is generally thicker and in a thick mash proteolytic action is said to be a little stronger.”
The Brewing Trade Review, October 1943, page 309.

I won’t pretend to understand the science there. It does seem underletting influenced the character of the finished beer. If you believe the scienticians.

Here’s a typical underlet mash schedule from my favourite London brewery. It was for a total grain weight of 9,408 lbs.:

1941 Barclay Perkins A and X Ale underlet mash
action	water (barrels)	water heat	goods heat
mash	56	154º F	147º F
underket after 30 mins	14	180º F	151º F
sparge	102	165º F	154º F
Source:
Barclay Perkins brewing record held at the London Metropolitan Archives, document number ACC/2305/01/624.