Fermentablility

Question: Is there any way to estimate the fermentability of your wort given what grains are used, what temperatures they're mashed at, and for how long?

I transferred my first AG batch to secondary a couple of days ago at a gravity reading of 1.009. I unfortunately didn't get an OG reading.

I was going to try to make a stab at my efficiency, but all my estimates are scaring me. So I'm hoping that the low FG is due to my mashing at 140º for 15 mins followed by 149º for 70 mins or so. Reading around, I've seen a couple folks talk about hitting attenuation rates upward 85% with the yeast I'm using (Wyeast 1275 Thames Valley.)

So either my efficiency was improbably poor, or it came out really fermentable - or most likely somewhere inbetween

[edit - typos]

You can get a general guess at OG just given the type and amount of grains you used. There's a chart and associated calculations in a book I have at home that give you optimum gravity based on the type and amount of grains used.

Your second variables of temperature and time would go into the multiplier of efficiency. Unfortunately, I don't know where to get this info off the web and can't remember the calculation off the top of my head.

I'll try to remember to post on this later.

Isn't it more complicated than that (for extreme accuracy, that is)? I would think that mash thickness would be an argument to the equation amongst other things.

I seem to get pretty close to OG targets using the Promash estimates for my grainbill and efficiency (65%). My FG, however, seems to consistently run ~2-4 pts lower. Who knows. I figure it makes me a cheaper date.

You're right BG, mash thickness is another variable. I'm guessing I came out on the thin side due to the added water I needed to get back up need where I wanted my temps.

I'm doing some more research on sugars and mashing and will update this thread shortly.

bear in mind that I am just a n00b, but Palmer's online book has a chapter dedicated to grain fermentability and calculating efficiency. It can be found at

http://www.howtobrew.com/section2/chapter12.html

All right. I've been poring over information that I'd like to share with the team. I apologize in advance for what is likely going to be a lengthy and fragmented presentation… so here it goes:

Sugars
Different sugars produced by the mash are metabolized by yeast at different rates and also affect the rate at which other sugars are metabolized.

A quick breakdown of some of the different sugars at work. Keep in mind these are just some of them: Carbohydrates

Wort composition / Sugars Found in Wort
Here is an excellent article describing this: Wort Composition
(also see John Palmers “How to Brew” for comparable table of the different sugars present in a given wort: Gravity vs Fermentability)
- If you haven't already, please take a quick look at the chart shown in the above article. You may note that only dextrins are listed as being completely unfermentable. All other sugars are fermentable to some degree under normal circumstances.

Fermentability
According to this article, sugars are fermented in this general order:
glucose & fructose (monosaccharides) -> Sucrose (simple disaccharide) -> Maltose (disaccharide) -> Maltotriose and other fermentable carbohydrates

- Note that the above progression is not entirely linear
- Yeast take in the monosaccharides directly, other sugars are broken down into monosaccharides via enzymes by the yeast before being used. Therefore the fermentability of a given polysaccharide is influenced by how well the enzymes can break it down to its comprising monosaccharides. Yeast primarily posses enzymes suited for breaking down maltose [maltase] and (depending on the yeast) maltotriose [maltotriase]
- Once again note the ratios of sugars present in a typical sample of wort
- The above article also discusses how higher gravity worts are more likely to get stuck due to the risk of catabolite repression – the deactivation of the enzyme needed to break down maltose
- Higher levels of glucose seem to lead to the retardation or deactivation of the maltase and maltotriase enzymes, so while glucose is perhaps easier for the yeast to use, the majority of your wort’s sugars maltose, so anything that impedes the breakdown of maltose will impact the fermentation as a whole significantly

Mashing
See Mashing and Mash temps, Enzymes, and Fermentability
- Here we see that different mashing temperatures affect the levels of activity of the two main enzymes responsible for converting the grains’ starches into sugars
- Beta-amylase enzymes are the prime producers of maltose and sucrose during mashing
- Alpha-amylase enzymes are needed to break the starches up to a point where the Beta-amylase enzymes can do their thing, while also producing sugars less favorable for fermentation: glucose, maltotriose, and dextrins
- Thicker worts tend to favor the Alpha enzyme while slightly thinner worts tend to favor the Beta, although as the temperature increases (approaching the upper range of the Beta enzyme’s optimal range), mashes thinner then 1.25 quarts / lb being to inhibit activity (see Mash Thickness vs Temp vs Extract)


Resources
Listing as many sources of information as I’m comfortable with, regardless if it was liked above or not.
Carbohydrates
Fermentability of Crystal Malts
Mash temps, Enzymes, and Fermentability
Mashing
Gravity vs Fermentability
Wort Composition
Mash Thickness vs Temp vs Extract

I suspect your low efficiency is due to too low a mash temperature. It wasn't hot enough for all of the starch to dissolve and alpha amylase is most active between 154 and 162F. The most common temperature used for single infusions is 152F, which is low enough for beta amylase to still work, but high enough for complete starch extraction and within the active range for alpha. I haven't talked to a single pro that uses anything except this method (not saying there aren't any). Stepping doesn't really help with modern pre-modified grains and it costs time, energy and efficiency.