A lady in our small town of Etna, California told me that she heard of using potatoes to brew beer — so I tried it! My spud ale came out quite good, but I need to do some refinement. Any advice?
Jack Tillman
Etna, California

When I was a graduate student at UC-Davis I attended a Master Brewers meeting at the local Sudwerk Privatbrauerei Hübsch brewery where I worked part-time as a brewer. The speaker at this particular meeting was a retired brewmaster from the Lucky Lager Brewing Company in San Francisco, which closed in 1978. The retired Lucky brewmaster talked about what he did during WWII to keep beer flowing from the brewery when corn and rice adjuncts were rationed and unavailable to brewers. He told of using potatoes as a replacement for rationed raw materials commonly used by brewers as adjunct grains. If my memory serves me right (this talk was given in 1993 or 1994) he used dried potato spuds. Before diving into this question I bought some dried potato spuds and verified that they are easy to handle and could have been received, stored and conveyed like other dry raw materials used by brewers. They also are extremely easy to hydrate.
   
So there is a precedent for potato beer. When you add potatoes to beer, be they boiled and mashed or dehydrated spuds, you must recognize that you are adding starch. This starch must be converted by amylase enzymes into fermentable sugars, just like any starchy brewing ingredient. The gelatinization temperature of potatoes is around 140 °F (60 °C) The other thing about potatoes is that they have a distinctive sulfur aroma and I would remove these compounds before fermentation. That’s another plus of using dehydrated potato spuds, since a lot of the sulfur aromatics in wet potatoes are driven off with moisture during the dehydration process.
   
The nice thing about potato starch is that it is not so different from barley starch. It normally contains a bit more amylose than barley starch (different varieties of potatoes and barley have different amylose and amylopectin profiles), but usually is about 50% amylose and 50% amylopectin. It also has a gelatinization temperature similar to barley starch (of course the dehydrated spuds are already gelatinized). What this means is that potato starch will behave quite normally in the mash and even if you decided to use “raw” potatoes instead of dehydrated spuds you would not have to boil the potatoes before mashing. If you shredded your tubers using a cheese grater as if preparing hash browns the potatoes will hydrolyze like the endosperm of malt when added to the mash.
   
I think the use of potatoes makes a lot of sense and you do have history on your side. But you also know now that their use by US brewers seems to have stopped after the rationing of food crops during WWII . . . so one has to wonder why it was discontinued. ‘Taters are certainly cheap, so my guess is that off aromas may be an issue in some cases.
   
If I were you I would brew some more batches, but would use step mashing to convert the potato starch into fermentable sugars.
   
While we’re on the subject, I have to admit that I have considered using potatoes for an Irish dry stout for a really geeky reason; Ashton, Idaho is known as the potato seed capital of the world, my name is Ashton and there was something in Ireland's history related to potatoes. Like I said, pretty geeky!


I started with 5-gallon (19-L) kits, but after about 30 batches I decided to double my capacity and brew all-grain 10-gallon (38-L) batches. My basic need is to convert a 5-gallon (19-L) recipe to 10-gallons (38 L). In the past I simply doubled the amount of each ingredient. Is this correct?
Glen Alden
Ormond Beach, Florida

In general terms, I agree that when recipes are scaled up in volume that the ingredients are simply not proportioned to the change in volume. The reason that this method normally does not work is that there are usually differences between the efficiencies of small and large brewhouses.
   
This scaling is often done when a commercial brewer is taking a batch of brew from their pilot brewery to a commercial size. Even in a small brewery this may mean scaling a 5-gallon (19-L) batch to a 15-barrel batch, or a 100-fold increase in volume. This jump in volume is significant because small differences in material efficiency become very apparent during this sort of scale change.
   
It is easy to demonstrate with standard brewhouse calculations that differences in brewhouse efficiency do affect wort original gravity. Also, the shape of your brew kettle and the type and size of heater used for the kettle can affect wort color, hop utilization and evaporative rate. These factors all are important if you want to make the same batch of beer twice on different scales.
   
All recipes published in BYO are based on assumed raw material yields. Since the actual efficiency of a particular brewhouse setup is fairly consistent and easy to calculate, those who brew frequently typically know their brewhouse efficiency and can modify recipes to account for the difference between an assumed efficiency and actual efficiency. Not all brewers calculate efficiency the same way, but the numbers are handy no matter the method. I prefer comparing how much extract I produce during wort production to the weight of malt used.
   
For example, let’s assume that I produce 20 liters of 12 °Plato wort and used 3.4 kg of malt in the process. My extract yield is equal to (liters wort)*(decimal equivalent of °Plato)*(equivalent specific gravity to Plato). You can convert Plato to specific gravity using the following formula:

Specific gravity = {Plato/(258.6-([Plato/258.2]*227.1)}+1

Once you determine that 12 °Plato is equivalent to 1.048, the rest of the calculation is easy. I have included units below to show how the units cancel, resulting in kg of extract:

(20 liter)*(0.12 kg extract/kg wort)*(1.048 kg wort/liter) = 2.52 kg extract

The 2.52 kg of extract represents what was extracted from the 3.4 kg of malt during wort production. When 2.52 kg is compared to 3.4 kg the result shows that 74% of the malt added to the mash ended up as extract in the wort.
   
Most homebrew set ups do not have a yield this high and a more typical number is 68%. So if I gave you one of my recipes and told you that my brewhouse yield was 74% you could easily adjust the malt bill accordingly by simply multiplying my malt bill by 1.09 (74 ÷ 68), assuming your brewhouse has a 68% efficiency.
   
Scaling up hops is much more difficult as there is no easy method homebrewers can use to determine how much iso-alpha-acids end up in their finished beers. When scaling recipes up and down without actually knowing hop utilization, brewers rely on rules of thumb, tables containing scaling factors and good old sensory evaluation.
   
However, if I were scaling a 5-gallon (19-L) batch up to a
10-gallon (38-L) batch I would be very tempted to just double the whole bloody recipe and forget the math. After all, we’re not blending something hazardous here, we’re brewing beer. If the result is off, then you can always tweak it next time.