SRM to EBC

Discussion on brewing beer from malt extract, hops, and yeast.
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sam c

SRM to EBC

Post by sam c » Mon Apr 27, 2009 12:50 pm

is there a way to convert SRM to EBC and EBC to SRM? i had a quick search but didn't find anything. my beer engine is EBC but alot of the recipes online are in SRM.

cheers

steve_flack

Re: SRM to EBC

Post by steve_flack » Mon Apr 27, 2009 1:08 pm

Approximately EBC is 2xSRM

sam c

Re: SRM to EBC

Post by sam c » Mon Apr 27, 2009 2:29 pm

cheers for that.

after searching around on the internet i found a coversion but im not sure if its correct or not?

EBC to SRM

EBC x .375 + .46

SRM to EBC

SRM x 2.65 - 1.2

anyone familliar with this?

Graham

Re: SRM to EBC

Post by Graham » Fri May 01, 2009 3:42 am

sam c wrote: after searching around on the internet i found a coversion but im not sure if its correct or not?

EBC to SRM

EBC x .375 + .46

SRM to EBC

SRM x 2.65 - 1.2
anyone familliar with this?
There is a certain complexity when one tries to convert between different colour standards, particularly between ASBC and IoB, but as Steve said earlier, using a factor of two for USA to British is fairly close.

Malt colour and beer colour are treated differently, though. A sometimes confusing aspect of colour determination is that at least three analytical methods are commonly employed:
IoB, Institute of Brewing (British).
ASBC, American Society of Brewing Chemists.
EBC (that other lot across the channel).

All three give different values, particularly with malt colour. Confusion abounds around the EBC issue because British maltsters and brewers (and Beer Engine) use the IoB methods unless otherwise stated, not EBC as is commonly supposed. IoB colour is specified as EBC because the EBC colour-glasses are used in the colour comparator - they were originally IoB colour-glasses anyway until the Europeans hi-jacked them. EBC methods and IoB methods are different for malt colour, except for the colour glasses, and give different results.

To elaborate on colour comparators and colour glasses: The original method of determining beer colour and malt colour was a visual method whereby north-light is shone through a sample of beer and compared side-by-side with coloured glass standards, which were a bit like photographic slides viewed through a stereo slide viewer, and the colour-glasses are changed or added to until the colour of the glasses and the colour of the beer match each other. The glasses are numbered according to their density which provides a Lovibond number. The gadget is known as a tintometer or colorimeter, and a modern version is still widely used (see Lovibond Tintometer 2000 or 3000).

The original colour-glasses are known as Series 52. The Series 52 (brown-scale) glasses were devised in 1885 and are based on a somewhat arbitrary scale. Because of their various limitations, in 1950 the British IoB abandoned the series 52 glasses in favour of what has now become the EBC glasses. Regretfully the Americans didn't - they still use Series 52. One of the problems with Series 52 is that they do not follow modern photometric optical laws. This means that American Lovibond (visual) does not correlate with SRM (an electronic photometric method). Therefore Lovibond and SRM are two entirely different scales. Although American home brewers claim that Lovibond and SRM are equivalent, they are not, except at very low (lager type) colours where they are close enough to not make much difference. The EBC glasses, on the other hand, more closely follow photometric laws, which was one of the several reasons for their introduction.

Although electronic, single-frequency photometric methods work for beer colour (sort of), they do not work too well for malt colour because the simple mini-mashed wort used for colour determination is unboiled and is therefore rich in protein. The protein absorbs and scatters the 430nm light source, making the readings erroneous. Electronic methods need a clear beer or wort with minimal suspended solids or proteins that would either scatter or absorb the light. Thus maltsters, even American ones, still use the visual, optical comparator for malt colour determination. This is why Americans use the term Lovibond (optical) for malt to distinguish it from SRM (electroinic) for beer; they are two different scales so a distinction is necessary for them. Regretfully the Europeans make no such distinction, although the EBC colour scale does follow optical density laws more closely.

One gotcha is path length. Obviously, if you are going to shine a light through a sample of beer or wort, the width of that sample is going to make a difference to the amount of light that passes through and comes out the other side. A sample jar that is twice as "big" will absorb twice as much light and will appear twice as dark. Therefore colour has to be referenced to a path length. The Europeans, including the British, reference to a 25mm path length (was an inch before Europeanisation), but the American ASBC use a half-inch path length.

There is yet another gotcha, which is the density of mash employed to produce the wort used for colour determination. IoB standardise on 50 grammes of malt made up to 515 millilitres with water. This is a 10% w/v grain/water solution. The extra 15ml is meant to compensate for absorption in the husk of the grain and the filter paper used, but it doesn't quite manage it because things have changed since the days when the method was devised. However, with fermentable extract determination (which uses the same mash) the results are mathematically normalised to exactly a 10% solution, but with colour they don't bother, presumably because there is only 1.3% error which they deem to be insignificant. The Americans and mainland Europeans use a 450 grammes mash, being 50 grammes of malt made up to 450 grammes with water which is a denser mash, producing a slightly higher colour.

I was told by a British maltster that all maltsters worldwide use a 10% mash, or mathematically normalise to a 10% mash, for malt colour determination as a standard. The Handbook of Brewing by W. Harwick also implies this, stating 50g of malt per 450g of water is used for colour determination, but I now have my doubts as to the truth of this. It is possibly an error or bad wording. As I do not have access to EBC Analytica or the ASBC documents (the ASBC book is $900 and the EBC book is similarly extortionately priced) I cannot easily determine whether or not that is true, so I assume that it is not the case and that the results are unadjusted. Incidentally the British IoB methods also permit a 450 gramme mash as an option, but that is mathematically adjusted to represent the 515 ml mash or 10% w/v solution. All IoB figures, no matter what density of test mash is used, are always expressed as if it was the standard 515ml mash.

Anyway, the upshot of all this is that to convert ASBC Lovibond malt colours to IoB malt colours we have to compensate for the difference between Series 52 and EBC colour glasses; compensate for the difference in path lengths employed; and compensate for the differing mash densities.

The formula given above: colour EBC = Lov x 2.65 -1.2 is fair enough, but working the other way would logically be: Lov = (EBC + 1.2)/2.65, not the other formula given in the quotation above. It does not make sense to use one formula to convert in one direction and an unrelated formula to convert in the opposite direction, even though the difference is small. It is another of those absurdities that often surface in brewing.

The Lov = (EBC + 1.2)/2.65 compensates for the difference between series 52 and EBC colour glasses and also for path length, but not for mash density. To convert between ASBC and IoB malt colours we need to compensate for mash density as well.

Without going too deeply into how the figures were derived, the following give conversion factors that I have derived (for malt colour).

ASBC to IoB = Lov *2.218-1.2 (compensates for colour glasses, mash density and path length)
IoB to ASBC = (IoB +1.2)/2.218 (ditto)

EBC to IoB = EBC*0.8368 (compensates for mash density only)
IoB to EBC = IoB/0.8368 (ditto)

ASBC to EBC = Lov * 2.65 -1.2 (compensates for colour glasses and path length)
EBC to ASBC = (EBC +1.2)/2.65 (ditto)

The above formula use the IoB method of converting between a 450g mash and a 515ml mash, and assumes that the 450g mash produces a 8.6°Plato (1.035) wort. It is a bit simplistic, but making it more complicated does not make enough difference to worry about, and only then with very dark malts. If you produce a table in a spreadsheet or something, you will observe that using EBC = 2xLovibond, as Steve has already pointed out, is close enough over normal ranges. Malt colour is hard to control at manufacture and has wide uncertainty spreads anyway, particularly with dark malts.

The above is formula is only true for malt colour. Beer colour is different yet again. Converting between EBC and IoB beer colour is not a problem; they are the same. Converting between ASBC and the others can present a problem though, because the Americans use an 1885 scale of colour glasses which bears little relation to the modern world. Americans generally specify beer colour in SRM. It would be fine if SRM really meant SRM. American 430nm photometric methods differ from European/British 430nm photometric methods only in path length. That is half-inch versus 25mm = 12.7/25 = 1.97. Simply dividing or multiplying by 2 as appropriate will perform the conversion. It can also be assumed that EBC colour glasses track photometric density well enough, so the 1.97 (or 2) multiplier is good too, no matter whether EBC is determined visually or photometrically.

However, if SRM is adjusted SRM there is a problem. By adjusted SRM I mean a beer that has been measured photometrically, but then adjusted mathematically to match the Series 52 glasses or Lovibond. Or a beer that has been measured visually but expressed as SRM. As mentioned before, the problem with the S-52 glasses is that they are irregularly spaced, do not accurately follow the optical laws, and are the wrong colour. This was of little consequence in the early days when American beers were typically very pale lager-coloured, but now that British and Belgian style beers are popular and widely brewed, they are in a bit of a dilemma because neither the Series 52 glasses or the 430nm photometric methods are really up to the job. Nevertheless, if we have to convert from Lovibond or pseudo Lovibond, we are forced to jump through the EBC = Lov * 2.65 -1.2 hoops.

There is a limitation with 430nm electronic photometric measurement inasmuch as it can only measure optical density, not colour. A beer with a proportion of crystal malt in its grist will have a red hue. Another beer that has a small quantity of black malt will have a brown hue. Both can have an identical optical density as far as the machine is concerned, but will be a different colour to a human observer. A visual comparator combines elements of both colour and optical density. A human observer peering through the viewfinder of a visual comparator will notice if either the colour or density does not match, but the electronic machine does not detect the colour difference.

As the whole purpose of controlling beer colour is so as not to surprise or offend the drinker, the old-fashioned visual method is far better at colour determination than the electronic machine, or at least the type of machine that they have chosen for the job. Although there are technical objections to the visual method, mostly because it relies on human perception, and because errors can occur if the colour of the glasses (which have fixed gradients) do not exactly match colour of the beer (different colours give different perceptions of density), it is still much better at the job than the electronic method. Measuring the colour of the same beer using the visual method and the electronic method will often come up with different numbers because the perceived density is different to true density due to the colour, but the colour-glasses still reign king and always have the final say, because they best represent what the customer actually sees.

Single-frequency (430nm) electronic photometric method is fine for brewery internal quality control checks, so that the brewer can quickly check if things are deviating from the norm, but it isn't any good at absolute colour. Internal quality control checks are what it is all about after all. Outside of the brewery, it is only twits like us that are interested in the colour rating of a beer, or even know what it means. It is quite common for British brewers to devise frig factors for each of their beers so that the measured photometric numbers tally with the visually derived numbers.

It seems that Americans do the same thing as well. On the net earlier (HERE) I found this:
"Large commercial breweries continue to use spectrophotometry for color determination even for the amber and dark beers they started brewing in recent years. Their approach has typically been to develop new in-house correction factors for each of their brews which allows them to match up absorbance with the Lovibond scale within the range of variations seen in production."

So the complexity or simplicity of the matter is determined by whether the brewery concerned quotes real SRM or adjusted SRM. This is probably brewery specific and we have no way of knowing what they really specify, so as they state SRM we must assume that they really mean SRM, and therefore simple path-length compensation is the best approach for beer colour - meaning multiply or divide by 1.97 (or 2 if you want to save finger fatigue).

How is it that Steve managed to say "2" in a lot less words?

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simple one
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Re: SRM to EBC

Post by simple one » Fri May 01, 2009 4:09 am

Quality post graham. Always been confused about colour issues. And now I know why!
Currently serving - Maltmillers Oatmeal stout - Bottled, Pale Rye APA - FV

sam c

Re: SRM to EBC

Post by sam c » Fri May 01, 2009 9:49 am

wow.

ever since i joined this forum i have been well impressed at the lengths people will go to help a fellow brewer,but that was insane!!

thanks very much for that mad amount of info even though it will probably take me a good few reads to take it all in.to be honest i was quite releaved that it can be roughly worked out by just x2, thank god!!

cheers


p.s i take it you are the man with the book, which i will definately by buying when im back in england.

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