Starch test

[Banjoblue]

So, if a starch test shows no starch left in the mash after say, 45 minutes into a 60 minute mash, does that mean I’ve got full conversion and can safely end the mash? Or are there other things to happen in the mash and I should give it full time?

 

[Sadfield]

Conversion is only the first part of the mash, converting starch to sugar, further time is required to get the desired types of sugar in the wort. A short mash time will give more large, complex and difficult to ferment sugars, a long mash time will give simpler, more fermentable sugars. Short mash will give a fuller, lower Abv beer, a longer mash will give a drier, higher Abv beer.

A good analogy is, felling trees converts them into wood that can be used for fuel. However, further time chopping is required to remove the branches, cut the trunks into manageable logs. Then, even more time is required to split those logs into wood that will fit into a fireplace.

 

[Banjoblue]

That’s interesting and helpful. So what is the point of a starch test?

 

[MmmBeer]

Conversion is only the first part of the mash, converting starch to sugar, further time is required to get the desired types of sugar in the wort. A short mash time will give more large, complex and difficult to ferment sugars, a long mash time will give simpler, more fermentable sugars. Short mash will give a fuller, lower Abv beer, a longer mash will give a drier, higher Abv beer.

A good analogy is, felling trees converts them into wood that can be used for fuel. However, further time chopping is required to remove the branches, cut the trunks into manageable logs. Then, even more time is required to split those logs into wood that will fit into a fireplace.

There is another variable, temperature. Higher mash temperatures (~67°C) favour the action of alpha amylase, which produces random complex sugars and lower temperatures (~62°C) favour the action of beta amylase, which produces more of the simple and highly fermentable sugars.

The usual compromise is to mash at 65°C, where both enzymes can do their required job, but if you want a beer with a dry finish reduce mash temperature by a degree of two, or if you want a richer, sweeter beer with more mouthfeel, increase by a degree or two.

If however you are going for dry finish, beta amylase does not act as fast as alpha, so you may need to allow a longer mash time, the starch test is a useful tool in determining whether conversion is complete.

 

[Banjoblue]

Thankyou, yes I understand (broadly) the impact of temperature and that was my understanding of the starch test too. But does temperature continue to determine the proportion of complex to simple sugars once starch conversion has finished? Do alpha and beta amylase operate only during the starch conversion process or do they continue to act once all the starch is converted?

 

[peebee]

... So what is the point of a starch test?

Good question!

Several answers:
To waste time.
To create unnecessary anxiety.
…

I have to admit I don't attempt to do one any longer. I think the last one I did was 45 years ago. The grain went black, they all did that.


To answer your later question … the amylases operate as long as there is something to operate on. We pick a temperature that will get the job done quickest, but it is also hot enough to slowly destroy the enzyme. It's a compromise between speed of action and destruction (there isn't some magic temperature where all the enzymes instantaneously destruct … although I guess they don't hang on long in boiling temperatures!). Bear in mind the enzymes were for the benefit of barley embryo in the not so warm ground.

 

[Sadfield]

That’s interesting and helpful. So what is the point of a starch test?

It's a confirmation that conversion has completed successfully. Ordinarily, it's not really required as most standard mashing conditions will convert, but it's useful as an assurance for a beginner who's learning the process, or for more experienced brewers who are pushing some of the many variables in mashing or using significant proportions of unmalted grains. Time, temperature, pH, water composition all play their part.
It's important though, when doing this test that you add the Iodine to wort, not grain. The husk of the grain will give a false reading.

 

[BREWERS DROOP]

Only time i do an iodine test is when using a large amount of flaked oats in the mash, dont bother any other time.

 

[Banjoblue]

Thanks all. I used the test a couple of times and had confirmation of full conversion. I’ll bear the comment about flaked oats in mind.