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Mash Day


Working on Brew-in-a-Bag principles, the first big day is when you ‘mash’ your grains in hot water and then boil the resulting wort with hops. This is the day which is most like cookery and benefits from the kitchen approach known as mise en place (everything in its place). Unless you have a well-stocked ingredients cupboard or live near a decent homebrew shop that probably means starting a few days earlier.

The starting point is the recipe you are going to use, from which you can work out suitable quantities of all the ingredients. Recently I’ve been brewing with 10l of water, so I express all the quantities in terms of grams and use a spreadsheet to identify a suitable factor to multiply them by (typically about 3.5 for Graham Wheeler’s recipes). That reckoning should also include the yeast, even thought that will stay in the packet until the day after mash day. You also need to assemble other items – a large stockpot (to hold all the liquid + 2-3l headroom for coping with the grain bag and boiling), a fine nylon mesh bag, a sealable container that can hold the wort straight after boiling (I use a heavy duty plastic jerry can), various jugs, funnels and utensils, a large bowl and colander, kitchen scales (which can measure to 1 or even 0.5g) and an accurate thermometer. Oh, and some cleaning chemicals, like VWP powder.

Start by giving your brewing area – probably the kitchen – a good tidy up. That means washing up, drying up and putting away! Clear surfaces are easier to clean and mean a safer space to work. Now use the chemicals to clean and sanitise the area and equipment. VWP rehydrated with warm water works well. Remember to wipe down surfaces before you put clean things on them and remember that the VWP solution needs a bit of contact time to work and to be rinsed off after for things that will touch the beer or other food stuffs.

Gather the ingredients together. I normally measure the water first and you can start heating that. Grains need to be measured into the bag (put that in the bowl). Deal with the main volume first (probably pre-crushed pale malt) and then use another bowl or bowls to weigh out the others. Uncrushed grains need breaking up although they don’t need to be turned into flour – a pestle and mortar works for small amounts. Mix all the grains together so different varieties are well distributed.

That’s probably all you need for the first stage so turn back to the water. Typically you will be mashing somewhere round 66°C, as instructed by the recipe, so you be aiming for a strike temperature of about 70°C. My induction hob is quite efficient at heating – otherwise you could extract some of the water, boil in a kettle and return to the pot. There is probably a formula for how much X ml of boiling water will raise the temperature of Y ml of water in the pot – or make an informed guess – in either case measuring the result.

Once at 70°C, gently lower the grain bag into the pot and stir to make sure it is all hydrated. Tweak the heat as required to get close to your mash temperature and start your timer for 60-90 minutes. Wheeler tends to go for 90 minutes; I’ve found 60 is normally sufficient but often split the difference at 75°C. While the clock is ticking, monitor the temperature periodically and keep as close to the mash temperature as possible. There is a small range during which the enzymes which convert grain starch to sugar will be active (about 60-70°C) but different types of enzyme work in narrower ranges and will denature if held above it for too long so, without more precise temperature control or lots of insulation on the pot, you will be taking readings quite often.

In between reading the temperature, measure out the other ingredients. There will be hops and possibly some sugar for the start of the boil and perhaps some more additions at timed stages towards the end and after the boil has finished; get them all lined up now.

Once mashing is done, gently lift the grain bag out. There will be a lot of liquid to drain out. Once it starts to drip rather than pour under gravity, I transfer it to the colander, sitting back in the bowl used earlier. As further wort drains out (and it can be squeezed as it cools), that can be added back to the pot. You might want to wear thick rubber gloves, which will let you squeeze the bag earlier but be very careful not to drop it back into the pot – hot sticky wort is not only potentially hazardous but a pain to clean up (voice of experience from boil over events!).

Turn the hob up to full and watch it come to a rolling boil. Resist the temptation to turn your back as it will make the final transition, with the attendant volume increase, very quickly when it get there. Back off the heat a bit, add your start of boil ingredients and set the timer going. The same considerations apply as for mashing – I make a note of what I did so I can tweak each variable individually in a future batch. However, you might want to time until the next addition rather than to the end of the boil (eg. 65 minutes and then 10 minutes).

You are now getting towards the end of mash day. Stir the pot from time to time – you can scrape down the foam which sticks to the sides – and make sure it keeps at a decent boil rather than a slow simmer. Keep the lid off – evaporation is condensing the wort a little and driving off unwanted volatile compounds. That means a hot and steamy kitchen so crack the windows a little, close doors into the rest of the house and, if you’ve got a dehumidifier, let it prove its worth.

After the boil and any final additions, you need to transfer the wort into a container for overnight cooling. I use that plastic jerry can, which I put in the sink. I put a large funnel in the neck and then use a ladle – both sanitised – to transfer enough wort to act as ballast. I then carefully pour the rest in, fully aware that it is a sticky, scalding liquid. I don’t worry about straining out the trub at the bottom of the pot – there will be some deposits left but most of it goes in. Once the lid is sealed, I swill the contents around so that all the internal surfaces are scalded clean – oven gloves and a lot of care are also applied here.

Set that container aside somewhere cool and it can drop to room temperature overnight. Tidy up the kitchen. Spent grains can go on the compost heap although you can also set some aside if you plan on doing something like baking bread later (they work well to spread over the top of the loaf while it is having its final, pre-oven rest). Oh, and if you haven’t already, treat yourself to a beer!