Mini-BIAB batch size discussion

[Mods, I've started this thread here rather than clutter up the 'my first post' thread.]
Invariably questions about stovetop batch size and brewlength come up. Here's one recent question to start the ball rolling.
CShenk asks:

CSchenk wrote:This site has been great for researching the BIAB technique. I'm trying to work out a recipe to try (thinking about the APA listed here) that fits my equipment. Currently I have a 20L pot to boil in. Any rough ideas on how large of a batch I could make?

Yep CSchenk, as hashie relates, the cheap and plentiful 19L stockpot is my main weapon and Maxi-BIAB is the way I get bigger batches out of it (not sure if that's what you're after though?). The method has a few sneaky clever tricks which makes life a bit easier as well, so I do recommend it, but maybe try Mini-BIAB first to get a more wholesome BIAB experience, if you do that you should be able to get 13 or 14L per batch in that stockpot.
Now, with Maxi-BIAB you should be able to brew 23- 25L batches with relative ease, I do that pretty much all of the time, I've not done more than 25L but I don't have too many doubts about being able to do 30L of lower- strength beer (say around 3- 4% abv). The main reason I haven't done the bigger run is that I don't actually have a fermenter big enough, so it is pointless really unless I had a use for an extra 5L of wort (haven't until now).
Post- boil dilution is where the extra volume is made up, because we're adding just plain water obviously the wort (unfermented beer) is stronger than usual, but this doesn't cause any real problems and it is just a straight concentration- volume conversion. I usually mash 4.0 to 4.5kg of grain per batch, it generally yields 17L of about 1.070, so with a target gravity of 1.048, the maths go like this:
Actual SG / Target SG * Actual Volume , so 70 / 48 * 17L = 24.8L diluted, so the water added is 24.8 - 17 = 7.8L

As an aside, that example was a very efficient mash from 4.0kg base malt, 0.17kg specialty malt and 0.2kg dextrose, the dex is to style in a UK Bitter but brewing dextrose/ sugar- friendly styles is another helpful way to ensure volume and gravity targets are met. Also the sophisticated ( ) method that I use for filtering the wort (a simple kitchen sieve! ) is about as efficient as it can get, so just about all of that 17L of concentrated wort is captured in the fermenter, this also helps keep overall efficiency high and the desired batch size achievable.

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Using a hydrometer jar to monitor fermentation.

Hi there potatoes and welcome to the forum .

I can't see any problems with a batch-size that small. Just scale down the instructions in, A Guide to Mini-BIAB and ask any questions that aren't clear.

Your first few batches might not turn out to exact gravity or volume expectations but should still give you very nice beer. Once you have two or three brews under your belt, you will get very close. So on the first few brews, plan and think ahead as to how and when you can take some measurements...

I would take a pre-boil one and then cool it. Once cooled and measured, return it to the boil.

A good hydrometer jar will often take over 200 mls to get a gravity reading and this might cause you some problems with further gravity readings so consider the following...

Take a post-boil gravity reading. Sanitise a coffee mug and dip it into the wort at the end of the boil (while the wort is still circulating), cover the mug in plastic wrap, put it in the freezer for say 20 - 30 mins (until it 'feels' slightly cool, say 20 C) and then pour it into your hydrometer tube. Take your post-boil reading which will be your original gravity.

Then, if you are using dried yeast, sprinkle 4 or 5 grains into the tube at the same time as you pitch your main yeast and then cover your entire hydrometer tube (hydrometer still in it) with something that will stop 'nasties' falling into the tube. Maybe use a large cut-off soft drink bottle with the neck cut off?

Keep your covered hydrometer tube in the same place as your fermenter and you will be able to watch the fermentation progress and tell when it has finished without taking further readings and wasting more wort.

The above is a great practice even in larger batch size BIABs but it will only work with a decent hydromer tube. Most tubes that come with your hydrometer are way too thin to even get good OG readings. Using such tubes in the manner I have mentioned above would be useless as the krausen etc will stop the tube moving.

Sorry about the long post but doing the above is a very efficient way of monitoring your fermentation - much better than watching an air-lock!

Will look forward to your results potatoes
PP

• • SVA Brewer With Over 100 Brews From Australia
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Good to hear potatoes...I'm glad you enjoyed it.

I'm a little surprised the oven didn't work very well. I wonder if your oven wasn't actually 70C, did you use a thermometer to measure the actual temp? 70C is usually at the low end of what an oven can achieve (mine is "warm", don't know the temp, then 200 F) so your oven may not be able to regulate at 70.

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potatoes wrote:Just did my second BIAB. This time the Oven worked a treat. Mash went in at 65c and stayed exactly 65c every time I gave it an occasional stir. I think that last time I was just checking on it too much. With Two mini BIABs under my belt, it might be time to move to a Maxi-Biab. Its a lot of work to make 5 litres of beer.

Congratulations potatoes!
Yeah, just leave the mash alone is my advice, regular stirring just loses heat and has precious little other benefit. IMO.
If the oven is too fiddly to get right every time, rest assured the thorough lagging method does work quite well. I use a jumper and a coat, usually lose around half a degC, which is fine. Preheating the surface where the pot will rest, first placing some insulation under it and preheating the lagging as well will all help, I just overshoot the strike water temperature and allow it to come back to where I want it through heat loss in preheating everything else.
You're quite right about the amount of effort required per unit volume of beer, that's precisely the reason the Maxi variant was developed!

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Hi Schober, well done on your first BIAB! That sounds quite reasonable to me and don't worry too much about skipping the mashout. Cheesecloth may not last more than a few batches, but it is an adequate stop gap so long as it drains adequately, but polyester fabric will last considerably longer. Adding water to the boil is acceptable to keep the volume up, but bear in mind it will only reduce the OG/ dilute the wort, it could be that the grain may not have been completely drained?
WRT the piddly brewlength with Mini-BIAB in a 19L kettle, that's pretty much the prime motivator for Maxi-BIAB. I do 23 and 25L batches routinely by this method, however I recommend novice all- grain brewers do try Mini-BIAB first, just to get familiar with the BIAB concept and iron out any issues before stepping it up to a slightly more complex process.

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