Compensating for excessive evaporation

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Col Robinson
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Compensating for excessive evaporation

Post by Col Robinson » Mon Nov 16, 2020 11:48 am

Hi, frequent lurker/very infrequent poster here.

One of my many failings as an all grain brewer is to have too vigorous a boil far too often. The last brew I did had an evaporation rate of 22.5% (I know it’s wrong to talk about evaporation rates in terms of percentages, for the sake of clarity, I lost 5.5 litres after starting out with 24.5 litres in the pot at the start of the boil.) To compensate for this I always take ‘excess spargings’ then top up the wort with these at the end of the boil until I get to the desired brew length.

I read that doing this is not great because apparently if the runnings are too thin then topping up with them could lead to introducing tannins to the finished beer. I must say I’ve done this for years and not noticed any adverse effects.

I’d like to know what others think about this practice of ‘topping up’. What do other brewers do when too much of their wort has evaporated? In the example above I topped up to 23 litres (the desired brew length) with 4 litres of what I call excess spargings – do people feel adding such a comparatively small amount really would introduce tannins to the level that would adversely affect the taste of the finished beer?

Many thanks in advance.

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Re: Compensating for excessive evaporation

Post by vacant » Mon Nov 16, 2020 3:56 pm

If your beer turns out fine why change?

Your "excess spargings" have been held at 60C plus for some time which is probably good enough but not as near sterile as wort after an open boil. I don't know about tannins.

Assuming boiler capacity is your problem, I would keep topping up during the boil except for the last 15 minutes. Reduce the boil time from e.g. 60m to 50m should stop a litre of loss.

Fitting a relay/thermostat/less powerful element? Extra expense. A vigorous boil is a good thing.
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Mashman
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Re: Compensating for excessive evaporation

Post by Mashman » Mon Nov 16, 2020 6:13 pm

Why not top up with water? It is water that has boiled off.
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Re: Compensating for excessive evaporation

Post by Col Robinson » Mon Nov 16, 2020 7:31 pm

[quote=vacant post_id=853747 time=1605538583 user_id=743]
If your beer turns out fine why change? Your "excess spargings" have been held at 60C plus for some time which is probably good enough but not as near sterile as wort after an open boil. I don't know about tannins.
[/quote]

I guess I have a vague idea that I want to do things 'right' plus I'm keen to know what other brewers do when they find they're short of a brew length due to excessive evaporation. That's a good point about the excess spargings being less than sterile. I've been doing this for decades though and (touch wood) haven't had an infection.

[quote=Mashman post_id=853748 time=1605546785 user_id=106]
Why not top up with water? It is water that has boiled off.
[/quote]

Of course! That's the answer! I did consider topping up with water but I thought I'd basically be diluting the beer. But I wouldn't would I, because as you say, it's only water that has boiled off. Plus I could just boil the kettle and use water from that which would put paid to the 'less than sterile' problem. I feel like a bit of an idiot now :oops: , but thanks for your thoughts, sincerely appreciated.

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Re: Compensating for excessive evaporation

Post by Mashman » Mon Nov 16, 2020 8:10 pm

My water is hard, 290 CaCo3. I use CRS for treatment. Occasionally I will use Tesco ashbeck for a special beer. I keep 2 or 4 litres in stock to replace evaporation or adjust OG. Never had a problem. Only downside is I hate the plastic waste.
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Re: Compensating for excessive evaporation

Post by Col Robinson » Mon Nov 16, 2020 9:14 pm

Can I ask why Tesco Ashbeck in particular? And wouldn't that still need to be boiled beforehand to sterilise it? I use CRS and DLS too, following a lab analysis from Murphy's.

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Re: Compensating for excessive evaporation

Post by Mashman » Mon Nov 16, 2020 10:30 pm

Ashbeck has a good reputation for brewing. I have used other supermarket spring water. I have used spring water for topping up for dozens of brews, never had a problem. Have done 96 brews on the Braumeister and probably as many on my old 3 vessel set up. Use spring water for dilution/top up regularly. I use beersmith to calculate the amount using the dilution tool.
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Re: Compensating for excessive evaporation

Post by Col Robinson » Mon Nov 16, 2020 11:25 pm

Thanks for that Mashman, I'll get in some Ashbeck next time I have a brew day just in case! I'm assuming you don't boil and you just top up straight from the bottle, as it were.

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Re: Compensating for excessive evaporation

Post by vacant » Tue Nov 17, 2020 9:29 am

Remember kit brewers add huge amounts of tap water without boiling it.
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Re: Compensating for excessive evaporation

Post by Cobnut » Tue Nov 17, 2020 9:39 am

why not simply allow for greater level of boil off? Unless you're limited on boiler space?

I sometimes top up my grainfather post-boil with additional sparge liquor to achieve a larger batch. I brew slightly stronger than I would for a normal 23 L batch (25L post-boil) and then add a further 7L before the chilling and transfer to fermenter. Works a treat, especially when my son is home from Uni and the beer consumption rises substantially!
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Re: Compensating for excessive evaporation

Post by london_lhr » Tue Nov 17, 2020 11:12 pm

One of the main reasons Ashbeck water is popular amongst brewers is that is is very low in alkalinity, in fact low in everything, and cheap.
This is the Ashbeck water profile :

Calcium 10.0
Magnesium 2.5
Sodium 9.0
Potassium 2.0
Bicarbonate 25.0
As CaCO3 20.5 (Calculated from the bicarbonate)
Chloride 12.0
Sulphate 10.0
Nitrate 11.0
If you want to brew with low alkalinity water (it is great for lagers) it is easy to add calcium and get the chloride:sulphate ratio to your liking.
Used it a lot before I started to treat my own water.
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Re: Compensating for excessive evaporation

Post by london_lhr » Tue Nov 17, 2020 11:51 pm

"I lost 5.5 litres after starting out with 24.5 litres in the pot at the start of the boil."

That doesn't sound like an excessive boiling loss.
On Sunday my pre-boil volume was 33l and post-boil volume was 26l for a 60 minute boil.
As a percentage that is very close to your figure.
I think your problem may be that your pre-boil volume may be too low to hit your post-boil target.
Also be careful of your "excess spargings" as you do not want the gravity of the sparge runnings to go below 1.011 to 1.015.
If you get to 1.010- 1.011 when sparging, it is better to add your sparge water directly to the copper rather than passing the water through the mash at a too low gravity. This way you will prevent extracting tannins.
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Re: Compensating for excessive evaporation

Post by brewbrew » Thu Nov 19, 2020 6:40 pm

Your boil-off is about the same as mine and I think is normal - a good rolling boil (with no lid) is good because it also blows off the DMS with the steam.

My approach is to recognise that I'm going to loose about 5 litres via the boil. I add 3 litres as extra water (not thin or aged runnings) at the start of the boil. Then when the wort has been cooled through the heat exchanger and collected in my fermentation vessel (that is graduated), I'll end up with somewhere between 1.5 and 2.5 litres short - I just make up with fresh tap water (I'm in a soft water area) or if I'm feeling flush and the family have not drunk all the (cheap) bottled water, I use that. If your boiler is too small to take the extra 3 litres, just add it all at the end (I have done that a few times and it is good). If you want to be pedantic, you can take some of the wort near the end of the boil, cool it and do an SG measure - then to be confident on your SG at yeast pitch, you can, with some nimble calculator work adjust the volume of the last bit of cold addition to get to target. If I'm low, I can miss out the final slug of cold or at least trim it back a bit to match desired SG (or if you are good, maybe add more water - but that never seems to be an opportunity - if my mash efficiency is out, it always seems to be under). In the summer, I pre-chill the final addition water to boost my heat exchanger's result and get nearer pitch perfection.

I have never had a problem

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Re: Compensating for excessive evaporation

Post by orlando » Sat Nov 21, 2020 8:13 am

Whatever you do don't back off of the rolling boil. Great things happen with that.
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