Beer strengths were being cut far more than in Holland. Where Lagerbier gravity was reduced in January 1941 to 7.8º Balling and Pils to 10.3º Balling. Compare that to the pitiful gravities below.
"VI. SITUATION IN BELGIUM.
Mr Stikker points out that the raw material position of the Belgian breweries is very bad. With effect from 1 January this year the gravity has been reduced again; only 6 days were given for its preparation. There are currently 3 beer types:
inn beer 1st category of 2° or +-5% Blg
" 2nd " “ 1.4° ” +-3.5% Blg
table beer " 0.8° " " +-2% "
It is to be expected that the Belgian breweries will be completely dry by April next.
Beer is only available for bread coupons in Belgium.
The free association of all Belgian breweries has been abolished and its place has been replaced by an official corporation within the framework of the Reichsnahrstand with compulsory membership and regulatory authority. At the head of this is Mr. Breedam. This body has recently introduced the above-mentioned gravity reduction. In addition, no more beer may be brewed of a higher quality than has been determined for sale."
Minutes of the management of the CBK on 21st January 1941, held at the Amsterdam City Archives, document number 31121-1, page 264.
The first gravity figures - 2º, 1.4º and 0.8º are Belgian degrees. The strengths would have been approximately 2% ABV, 1.4$ ABV and 0.8% ABV, Basically, not worth drinking. Even worse, some beer could only be obtained with bread coupons which the public was reluctant to use in this way.
"In Belgium, the system of dispensing beer on bread coupons would have been abolished, but this only applies to beer with a 2% original wort content. The breweries have large stocks of beer, but cannot sell it, as the public will not give up bread coupons."
Minutes of the management of the CBK on 5th March 1941, held at the Amsterdam City Archives, document number 31121-1, page 243.
The combination of higher taxes, bread coupons and low gravities was starting to seriosly damage the whole industry.
"The speaker pointed out that here in the Netherlands one should not be faced with the situation as in Belgium; there the breweries had little stock, while the coupon system makes it impossible to sell beer, so that the breweries are unable to afford the large reclaim due to the sharp increase in beer excise duty. The consequence of this is that the brewing industry has been damaged in a very serious way in Belgium, while the gravity there is particularly low. Some things resonated with Mr. Biel."
Minutes of the management of the CBK on 26th March 1941, held at the Amsterdam City Archives, document number 31121-1, page 229.
Six months later and gravities were cut again with the elimination of the strongest category of beer.
The maximum gravity is currently still there, but the levels will be reduced to 3.5% and 2% as of July 15th. Despite the presence of the occupying troops, turnover amounts to only 60% of that in 1940. In. Some Belgian circles are of the opinion that the reduction in turnover is a result of the series of reductions in gravity which have taken place which render the beer undrinkable and turn the public away from the beer."
Minutes of the management of the CBK on 4th July 1941, held at the Amsterdam City Archives, document number 31121-1, page 110.
Consumption of beer had collapsed and was continuing to fall. In contrast to Holland, where production had increased, albeit at lower gravities than before the war.
One of the committee disagreed that the low gravities were responsible for the marked decline in beer consumption.
"Mr. van Marwijk Kooy believes; that the reduced beer consumption in Belgium is not the result of the poorer beer quality, but of a lack of money on the part of the Belgian population, which has to spend much more money on food due to its very poor food position. A reduction in volume would be at the expense of the public, as the armed forces will continue to claim their normal quantum. For this reason, the Speaker considers a reduction in gravity, which is technically possible, to be preferable to a reduction in volume. In these times the public does not attach so much importance to quality; The main thing is that a product is still available."
Minutes of the management of the CBK on 4th July 1941, held at the Amsterdam City Archives, document number 31121-1, page 111.
My guess is that it was a combination of ridiculously weak beer and lack of money. Why waste cash on beer that was hardly worth drinking?