Has anyone tried diluting after initial active fermentation?

[user 287495]

Due to serious space constraints I'm using a Speidel 20L fermenter. Assume that's a given here. Despite 20L being 5.2 gallons, it holds maybe 5.7 gallons. Using fermcap, I brew 5 gallon batches in there.

Since it is not a lot of headspace, I use a blowoff tube for the first 3 days. When fermentation is particularly active, I get some foam in the blowoff tube, and dried foam gets caked on the fermenter lid.

I've suspect there are benefits to having the foam rise and fall back into the beer.

Respected homebrewer Jay Ankeney writes this:

With the closed single-stage approach, you brew up about 3 to 4 gallons of wort so your carboy is only three-quarters full when you pitch the yeast. Then wait for the fermenting foam to rise and fall, and top off the carboy with cool water that you have pre-boiled to sterilize. Although this is heresy to traditionalists ...
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I would like to start doing this. Ferment 4 gallons for 3 days, then top off with preboiled water.

Questions:
1) Does anyone do this regularly? How does it work out for you?
2) What do you do for the OG reading? If you'd used extract for 5 gallons in 4 gallons of water, it would be too sugary
3) What about topping off with 1 gallon of wort side aside after boil? That wort could be used for reading the OG.
4) I've heard you get estery beer when diluting if OG is high. Would this be a problem if just adding 1 gallon to 4?

I'm particularly interested in hearing from people who have actually tried this.

 

[Qhrumphf]

It's a bad plan. There's no harm in how you're currently doing things. Otherwise if you're that worried about blowoff just make smaller batches. Topping up with water post or late fermentation only serves to damage your beer, potentially seriously, with absolutely no benefit. It only makes sense in large commercial breweries as a stop-gap to expansion (and then extensive efforts must be made to minimize damage to product)

 

[Qhrumphf]

Topping up with wort is a better idea. Topping up with actively fermenting wort better than that (though in both cases you'll likely end up with blowoff again). If you can top up with fermented beer in a sanitary way without oxidizing either the initial batch or the top up (basically blending), that'd be the ideal and achieve your goal the best.

 

[IslandLizard]

Why not co-ferment the extra beer in a 2nd (small) fermenter? Such as a gallon wine jug? Then add it when packaging to get your intended batch volume.

 

[SanPancho]

Or make up the volume with wort, either from your batch you kept in fridge or freezer or just dme/lme. Perfect time to do priming with some cbc yeast. Works for kegs or bottles.